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Electrochemical Production of High-Concentration Ozone-Water Using Freestanding Perforated Diamond Electrodes
Journal of The Electrochemical Society
Abstract
High-concentration ozone-water can be directly produced with a zero-gap electrolytic cell containing a freestanding perforated boron-doped diamond electrode. For the sake of improving current efficiency for electrochemical ozone-water production, optimization of the electrode configuration was performed. It was proven that the number of holes, hole size, and electrode thickness affect current efficiency. In particular, increasing the number of holes per unit area was the most effective method for improving current efficiency. In regard to hole size, 1 mm diameter was more appropriate than 1.5 mm diameter. Electrode thickness affected the current efficiency, and maximum values were found to be around 0.5-0.6 mm. Based on these results, an electrode optimal for electrochemical ozone-water production was prepared and achieved a maximum current efficiency of 47% in moderate conditions thus far. (c) 2007 The Electrochemical Society.
... To achieve the maximum current efficiency, O 2ads should encounter and react with (O ⦁ ) ads before detachment from the surface as O 2 . As such, materials with high overpotentials for OER such as platinum (Pt) [7], high oxidation metal oxides (PbO 2 [8][9][10][11], TiO 2 [12], and doped SnO 2 [13]), glassy carbon (GC) [14] and boron-doped diamond (BDD) [15][16][17][18][19][20][21], have been investigated as anodes for EOP. BDD electrodes are especially desirable, since there are no concerns about heavy metal contamination [18] and they can be operated in aqueous solutions at room temperature. ...
... As such, materials with high overpotentials for OER such as platinum (Pt) [7], high oxidation metal oxides (PbO 2 [8][9][10][11], TiO 2 [12], and doped SnO 2 [13]), glassy carbon (GC) [14] and boron-doped diamond (BDD) [15][16][17][18][19][20][21], have been investigated as anodes for EOP. BDD electrodes are especially desirable, since there are no concerns about heavy metal contamination [18] and they can be operated in aqueous solutions at room temperature. ...
... For EOP applications, (high purity) water is the preferred feedstock, as ions associated with deliberately added electrolytes or tap water may also undergo electrochemical conversion, reducing EOP current efficiency and producing unwanted by-products, such as chlorine [17]. When using water, a solid electrolyte is required, typically a Nafion membrane, sandwiched between two perforated BDD electrodes [17,22], a configuration referred to as a zero-gap cell (ZGC) [11,18,20]. To perforate the BDD i.e. introduce holes all the way through the material, referred to as "through-holes", two methods are typically employed. ...
... 1.51 1 2 3 Efficient EOP requires an anode that electrocatalytically favors EOP over the oxygen evolution reaction (OER). The electrode materials which have shown most promise are synthetic boron doped diamond (BDD), [10][11][12][13][14][15][16] PbO 2 , 17 TiO 2 , 18 and Ni/Sb doped SnO 2 . 19 BDD is particularly interesting as it presents no heavy metal contamination issues and exhibits a very wide anodic solvent window in water due to sluggish OER. ...
... In water only, a Nafion® separating membrane is essential, functioning as both a solid electrolyte and as a proton transporter. Perforated, i.e. containing through-holes, freestanding BDD electrodes have also been used in ozone generation, 14,15 designed with an aim to maximize contact between the BDD, solution and the Nafion® membrane. 15 Freestanding BDD electrodes offer the advantages of superior robustness, higher efficiency, durability and stability over long time periods. ...
... Perforated, i.e. containing through-holes, freestanding BDD electrodes have also been used in ozone generation, 14,15 designed with an aim to maximize contact between the BDD, solution and the Nafion® membrane. 15 Freestanding BDD electrodes offer the advantages of superior robustness, higher efficiency, durability and stability over long time periods. Thin film BDD electrodes can develop pin holes and eventually delaminate. ...
Electrochemical ozone production (EOP) from water is an attractive, green technology for disinfection. Boron doped diamond (BDD) electrodes, grown by chemical vapor deposition (CVD), have been widely adopted for EOP due to their wide anodic window in water and excellent chemical and electrochemical stability. High pressure high temperature (HPHT) synthesis, an alternative growth technique used predominantly for the high-volume synthesis of nitrogen doped diamond microparticles, has been seldom employed for the production of conductive BDD electrodes. In this letter, we demonstrate, for the first time, the use of BDD electrodes fabricated from HPHT conductive BDD microparticles for EOP. The BDD microparticles are first compacted to produce freestanding solid electrodes and then laser micromachined to produce a perforated electrode. The compacted HPHT BDD microparticle electrodes are shown to exhibit high EOP, producing 2.23 ± 0.07 mg L-1 of ozone per ampere of current, at consistent levels for a continuous 20 hr period with no drop off in performance. The HPHT electrodes also achieve a reasonable current efficiency of 23%, at a current density of 770 mA cm-2.
... 10 Efficient EOP requires an anode that electrocatalytically favors EOP over the oxygen evolution reaction (OER). The electrode materials which have shown most promise are synthetic boron doped diamond (BDD), [11][12][13][14][15][16][17] PbO2, 18 TiO2, 19 and Ni/Sb doped SnO2. 20 BDD is particularly interesting as it presents no heavy metal contamination issues, exhibits a very wide anodic solvent window in water due to OER being disfavored and experiences minimal electrochemical corrosion during operation, unlike materials such as PbO2 and doped SnO2. ...
... 21,22 The BDD is either grown in thin film form, where it remains attached to the growth substrate, or thick enough so that it can be removed and is freestanding. Thin film BDD [11][12][13][14][15][16][17] has been used for EOP with either water, 13,14,17 sulfuric acid, 11,12 or perchloric acid 12 as the electrolyte. In water, a Nafion® separating membrane is essential, functioning as both a solid electrolyte and as a proton transporter. ...
... In water, a Nafion® separating membrane is essential, functioning as both a solid electrolyte and as a proton transporter. Perforated freestanding BDD electrodes have also been used in ozone generation, 15,16 designed with an aim to maximize contact between BDD, solution and the Nafion® membrane. 16 Freestanding BDD electrodes offer the advantages of superior robustness, higher efficiency, durability and stability over long time periods. ...
Electrochemical ozone production (EOP) from water is an attractive, green technology for disinfection. Boron doped diamond (BDD) electrodes, grown by chemical vapor deposition (CVD), have been widely adopted for EOP due to their wide anodic window in water and excellent chemical and electrochemical stability. High pressure high temperature (HPHT) synthesis, an alternative growth technique used predominantly for the high-volume synthesis of nitrogen doped diamond microparticles, has been seldom employed for the production of conductive BDD electrodes. In this letter, we demonstrate, for the first time, the use of BDD electrodes fabricated from HPHT conductive BDD microparticles for EOP. The BDD microparticles are first compacted to produce freestanding solid electrodes and then laser micromachined to produce a perforated electrode. The HPHT BDD electrodes are shown to exhibit high EOP, producing 2.23 ± 0.07 mg L-1 of ozone per ampere of current, at consistent levels for a continuous 20 hr period with no drop off in performance.
... Among the investigated anode materials, the following can be men- tioned: glassy carbon [32,48], Ni/Sb-SnO 2 [49], IrO 2 -Nb 2 O 5 [50,51], tanta- lum oxide [52][53][54], TiO 2 [55][56][57], and boron doped diamond (BDD) [34,38,[58][59][60][61]. In the case of IrO 2 -Nb 2 O 5 , it obtained a lower current effi- ciency of ozone at 0°C in 3.0M H 2 SO 4 (1%), increasing up to 12% when 0.03 M KPF 6 [50] was employed as a supporting electrolyte by applying 800 mA cm À2 . ...
... Also, these anodes are inert and with poor adsorptive qualities [62]. A few studies have reported the electrochemical O 3 gener- ation by BDD electrolysis ( [34,38,[58][59][60][61]. Michaud and coworkers report that the main product of water electrolysis in H 2 SO 4 is peroxydisulfate (S 2 O 8 2À ), and in HClO 4 the reactive oxygen species, such as hydrogen per- oxide, hydroxyl radicals, and ozone [34,63]. ...
... Both Michaud et al. [34] and Katsuki et al. [60] report lower ozone current efficiencies with BDD anodes in aqueous acidic solutions in divided cells. Conversely, researchers inves- tigated the electrolysis of deionized water (<1 μS cm À1 ) using zero gap cells with Nafion membranes, achieving current efficiencies of 24% and 47% for ozone production, respectively [58,59,62]. ...
... To achieve the required productivity level, separate electrochemical elements are combined into a fi lter-press structure (stack of electrochemical cells). Water electrolyzers with SPE commonly use a cathode based on Pt (e.g., Pt or Pt/Ti), and, when water is delivered to the anode, the cathodic reaction (5) is the evolution of hydrogen [20][21][22][23]. If, however, only ozone is the target product, the air cathode (e.g., Pt/C, where C is a carbon fabric or paper) can be regarded as an alternative in which the cathodic reaction consists in the reduction of oxygen to water, accompanied by the formation of hydrogen peroxide by reactions (6a)-(6c) [1,18,[24][25][26]: ...
... The positive effect of low temperatures on the current effi ciency by ozone on Pt-based electrodes was observed rather long ago and later confi rmed in studies of other anode materials [9,27,44]. However, it has been reported that the effi ciency of ozone release on PbO 2 falls as temperature is lowered [21,51], and there have been quite a number of studies in which a high current effi ciency by ozone was obtained at room temperature [18,23,52]. In addition, it is known that anions can strongly affect the ozone formation effi ciency, which is considered below. ...
... Both in [100] and in [110], the current effi ciency of ozone generation Ti support was only several percent in performing the process in a cell with a liquid electrolyte in which the anode and cathode spaces are separated by a Nafi on® membrane. By contrast, the current effi ciency obtained in [99] and [23,52] in electrolyses of deionized (<1 μS cm -1 ) water in a cell with an SPE reached values of 24 and 47%, respectively. A possible reason is that the adsorption of anions unfavorably affects the formation of ozone at a BDD electrode, e.g., by inhibition of reaction (8) and(or) (13) due to the interaction of anions and active oxygencontaining species upon their approach to each other [52]. ...
Mechanisms of ozone generation in an electrochemical system with a solid polymer electrolyte and the electrode and catalytic materials used in systems of this kind are considered. The influence exerted by the process parameters and by the type of electrolyte and electrocatalysts on the productivity of the system and on the current efficiency by ozone is analyzed.
... Ozone is an environmentally friendly and powerful oxidant because it leaves no harmful by-products after a reaction and has a high redox potential [1,2]. Because of this, it is widely used in a variety of applications, such as disinfection, cleaning, bleaching, wastewater treatment, and water treatment [3,4]. ...
... Because of this, it is widely used in a variety of applications, such as disinfection, cleaning, bleaching, wastewater treatment, and water treatment [3,4]. The most common technology for ozone production, the corona discharge process, has several disadvantages such as producing ozone at low concentrations (~2 wt.%) and maintaining a cooling system, drying system, and ozone diffuser [1,[5][6][7]. On the other hand, electrochemical ozone production (EOP) technology has attracted much attention [8] as an alternative to the conventional corona discharge technology. ...
... produces a high concentration of ozone in water [3,9]. Electrodes composed of PbO 2 [9][10][11][12], SnO 2 [6,13,14], and boron-doped diamond (BDD) with high oxygen overpotential [1,[15][16][17] are popular anode materials for ozone production. Inert supporting electrolytes (SEs) in EOP is essential to provide the electrical conductivity of water electrolysis. ...
This study investigated how inert supporting electrolytes (SEs), which increase the electrical conductivity, affect electrochemical ozone production (EOP) on a boron-doped diamond (BDD) electrode. Regardless of the SE species, the EOP was suppressed about 60% in a SE concentration of 1 mM for which the conductivity is similar to that of tap water compared to deionized water. The production of H2O2, which is known to be generated by the combination of (Formula presented.), was also suppressed. On the other hand, the formation of (Formula presented.) was not significantly affected by the presence of SEs, an intermediate for ozone production. Consequently, suppression of EOP by SE can be explained by physical interference from the diffusion or combination of (Formula presented.) by the SE anions concentrated near the electrode surface. This study contributes by providing a better mechanistic understanding of the effect of SEs on EOP in a solid polymer electrolyte/BDD system.
... In recent years, a number of alternative materials have been reported as being active anodes for EOP 1 including: TiO 2 , 6-8 glassy carbon, 9 IrO 2 -Nb 2 O 5 , 10,11 tantalum oxide, 12,13 and more recently Ni/Sb-SnO 2 [14][15][16] and Boron Doped Diamond (BDD). [17][18][19][20][21] To date, only two electrode materials have proven capable of generating ozone with efficiencies > 20% at room temperature and using solutions that do not contain expensive fluorine-containing anions: Boron Doped Diamond (BDD) [17][18][19][20][21] and Ni/Sb-SnO 2 [14][15][16][22][23][24][25][26][27] In general, BDD anodes are employed primarily for the oxidation of species in solution, 28 via the production of OH radicals, 29,30 and have only shown high activity and selectivity toward the electrochemical generation of ozone in water containing no added electrolyte. It is not clear that ozone is expected to be a major product at such anodes. ...
... In recent years, a number of alternative materials have been reported as being active anodes for EOP 1 including: TiO 2 , 6-8 glassy carbon, 9 IrO 2 -Nb 2 O 5 , 10,11 tantalum oxide, 12,13 and more recently Ni/Sb-SnO 2 [14][15][16] and Boron Doped Diamond (BDD). [17][18][19][20][21] To date, only two electrode materials have proven capable of generating ozone with efficiencies > 20% at room temperature and using solutions that do not contain expensive fluorine-containing anions: Boron Doped Diamond (BDD) [17][18][19][20][21] and Ni/Sb-SnO 2 [14][15][16][22][23][24][25][26][27] In general, BDD anodes are employed primarily for the oxidation of species in solution, 28 via the production of OH radicals, 29,30 and have only shown high activity and selectivity toward the electrochemical generation of ozone in water containing no added electrolyte. It is not clear that ozone is expected to be a major product at such anodes. ...
... Ozone current efficiency is generally observed to increase with current density when using non-Ni/Sb-SnO 2 anodes (e.g. PbO 2 , Pt etc), 2,9,[17][18][19][38][39][40] at least up to a point, after which it either remains constant or decreases (most studies on the electrochemical generation of ozone employ constant current rather than constant potential or cell voltage); hence it does not seem unreasonable to postulate that the resistivity of the catalyst layer is likely to be an important factor in ozone activity. Undoped SnO 2 should be an insulator, and hence its resistivity of ca. ...
This paper reports the effect of employing Ni & Sb oxide precursors ( instead of chlorides) in the preparation of Ni/Sb-SnO2 anodes on the activity and selectivity of ozone production in 1.0M HClO4. The effect of catalyst loading, Ni content in the precursor solution, furnace temperature and constant current density vs constant cell voltage operation is reported. The optimum composition was found to be Sn: Sb: Ni = 100: 6: 1, giving a maximum current efficiency of ca. 38% at a current density of 100 mA cm(-2), the latter higher than previously reported. The durability of anodes prepared using NiO and Sb2O3 at 550 degrees C during electrolysis at 100 mA cm(-2) in 1M HClO4 was found to be 200 hours, again significantly higher than Ni/Sb-SnO2 anodes prepared using the chloride precursors at lower temperatures.
... Ozone production efficiency is competed by oxygen evolution that is thermodynamically favored at lower potential (1.23 V vs SHE). In order to have higher EOP efficiency, electrodes with high OER overpotential have been used, such as lead dioxide (181,192) and diamond (193). Moreover, it is worth to note that EOP is usually accomplished in pure water, and its efficiency tends to decrease in wastewater due to impurities (193,194). ...
... In order to have higher EOP efficiency, electrodes with high OER overpotential have been used, such as lead dioxide (181,192) and diamond (193). Moreover, it is worth to note that EOP is usually accomplished in pure water, and its efficiency tends to decrease in wastewater due to impurities (193,194). ...
Significant concerns continue to be raised over environmental pollution of soils and water resources. Chemical fate and transport coupled with redox manipulation are the primary processes that have been considered for removing contamination and minimizing exposure. Electrochemical processes utilize electron transfer to drive transport of chemicals and redox manipulation for treatment of contaminated media. Electrokinetic remediation relies on the electric field to transport contaminants in low permeability soils toward the electrode vicinity for removal. In water cleanup, both electroreduction and electrooxidation have been used. Electroreduction has been used for dechlorination and defluorination of halogenated calcitrant compounds. Electrooxidation has also gained significant potential for transformation of many legacy and emerging contaminants. For example, organic contaminants could be oxidized directly on anode surface (direct anodic oxidation), by electrochemically generated hydroxyl radicals or by other electrochemically generated oxidants (indirect anodic oxidation). In this article, we present an overview of the state‐of‐the‐art electrochemical processes for treatment of contaminated soil and water. We also describe a perspective for future research directions in the field of electrochemical treatment of contaminated media.
... These values are within the same range of those reported in the literature. Thus, Arihara and coworkers have reported 5.71 g (kWh) − 1 in ozone generation using a similar cell equipped with BDD as anode, Pt mesh as cathode and a Nafion membrane [40,41]. Values obtained are rather good as it is supported by the high faradaic efficiencies reported in Table 2 . ...
This work focuses on the scale-up of electro-ozonizers by evaluating the production of ozone and the degradation of clopyralid synthetic wastes using three commercial PEM electrolyzers. The mechanical concept of the three cells is similar: a single compartment cell equipped with a MEA (consisting of a polymer exchange membrane and two pressed diamond coatings electrodes), powered with monopolar electric connection and where water flows on the surface of the electrodes, although the main electrolyte is the Nafion proton exchange membrane. However, their size and recommended operating conditions are not as similar, and their comparison becomes a good scaleup case study. The CabECO® cell consists of 2 MEAs with a total surface area of 24 cm², a maximum operating current density of 2. 0A. The Mikrozom® cell consists of only one MEA with a net surface electrodic area of 112 mm² and a maximum operation current density of 1.0 A. Finally, the CONDIAPURE® cell consists of a single MEA with a total surface area of 146 cm² and a maximum operation current density of 10.0 A. The performance under mild and extreme operating conditions was compared and the results show that, although the cell concept is similar, the results obtained differ very significantly. The three PEM electrolyzers tested can produce ozone efficiently and mineralize completely clopyralid. The only intermediates measured come from the cathodic hydrodechlorination of clopyralid and oxidative intermediates were only detected at trace concentrations. CabECO® cell demonstrates an outstanding performance with very high current efficiencies in the production of ozone. However, the highest mineralization efficiencies are obtained with the Microzon®, which, although it is the PEM electrolyzer with the smallest active area, is the most efficient because can reach high ozone concentrations and achieve the best clopyralid mineralization. Efficiencies as high as 0.47 mg O3 Wh⁻¹ can be obtained with this cell. Slightly lower values are reached by the CabECO® cell (0.38 mg O3 Wh⁻¹). Enlarging electrode surface area does not seem to be a good strategy from the viewpoint of efficiency and it seems to promote side reactions that compete with ozone production and with the degradation of organics. This means that stacking rather than electrode enlarging should be the strategy more advisable for scaling up the electro-ozonation technology.
... It is assumed that a significant part of its oxidizing power is expended by the reaction with soil organic matter. Production of ozonated water had been highly inefficient until boron-doped diamond electrodes were developed for the continuous electrochemical generation of dissolved ozone directly from water (Arihara et al. 2007;Cobb et al. 2018). These electrodes became commercially available at various scales. ...
Phytonematodes cause severe yield losses in horticulture, partly because they are difficult to manage. Compact, energy-efficient generators that electrochemically produce ozonated water by utilizing diamond-coated electrodes have become available. In this study, the application of on-site generated ozonated water to inactivate soil nematodes and to mitigate nematode-mediated apple replant disease was tested. Pratylenchus penetrans was highly susceptible to dissolved ozone (LC 50 0.6 mg L ⁻¹ ). In one greenhouse experiment, treatment of P. penetrans in soil with ozonated water (0.27 mg ozone L ⁻¹ soil) reduced subsequent invasion of the nematodes into roots by 60%. Growth of apple saplings in soil that was affected by apple replant disease (ARD) was significantly improved following a treatment with 1/10 volume ozonated water compared to the control. In a second greenhouse experiment, one-time drenching of ARD soil with ozonated water was followed by improved growth of apple plants similar to that in autoclaved soil. A second application of ozonated water did not further improve plant growth. The number of active nematodes in replanted soil that moved through a Baermann filter was significantly reduced by all tested concentrations of ozone (0.12–0.75 mg L ⁻¹ soil). A fraction of 19–36% of the nematodes survived and slightly recovered after four weeks. In conclusion, on-site generated ozonated water has potential to mitigate nematode problems in horticulture and to expand management options.
... However, it is important to find the optimal concentration, because there is a conductivity from which the ozone concentration decreases due to increased anionic adsorption reduce the ozone yield [30,45,70]. The use of BDD electrodes or Pt with cells divided with Nafion membrane has allowed the generation of ozone in milder operating conditions such as pure water or artificial tap water, as it can be operated with low conductivities, increasing the current efficiency (CE) by 20% compared with other works [41,42,71]. Table 4 summarizes several of the recent applications in which electro-ozonizers have been applied. ...
In this work, the production of ozone at mild pH conditions using a commercial electrochemical PEM cell CONDIAPURE ® is evaluated, at once a phenomenological model is proposed to understand the basis of the processes that occur inside the cell. At these pH conditions, the production of ozone can be explained from the oxidation of water, while the decomposition of ozone is found to be extremely important to explain the global experimental behavior observed. Not only is this decomposition a chemical but also an electrochemically assisted process which, in turn, can be related to the production of other oxidants in the cell which interact with ozone behaving as predators. The model formulated explains and satisfactorily reproduces the influence of the operation mode, the current intensity applied and presence and destruction of organics, with regression coefficients (r²) ranging from 0.88 to 0.99, helping to understand how the production of ozone should be promoted during electrochemical processes.
... However, it is important to find the optimal concentration, because there is a conductivity from which the ozone concentration decreases due to increased anionic adsorption reduce the ozone yield [30,45,70]. The use of BDD electrodes or Pt with cells divided with Nafion membrane has allowed the generation of ozone in milder operating conditions such as pure water or artificial tap water, as it can be operated with low conductivities, increasing the current efficiency (CE) by 20% compared with other works [41,42,71]. Table 4 summarizes several of the recent applications in which electro-ozonizers have been applied. ...
Ozone is a rather attractive oxidant, it is very efficient in the oxidation of pollutants and in the killing of pathogens and does not generate any hazardous waste during its use. Its generation has been constantly sought in an effective way, focusing on obtaining high concentrations of ozone at the lowest possible cost. Recently, electrochemical production of ozone show advantages over conventional corona discharge generation, since this technology do not need very high voltages, feeding oxygen or pure air or dissolving the ozone into wastewater to be treated. However, it is still at early development stage and there is still a long way to reach the high technology readiness levels needed to complete its value chain. Equipment considerations and operation conditions are the key points that need to be understood in order to increase efficiently. Recent novelties in the state of the art of research are summarized in this work.
... [5][6][7][8] The latter is extremely useful for cutting and structuring wafer scale diamond (and BDD) films into much smaller, useable geometries. [9][10][11][12] ns-laser micromachining does however, introduce non-diamond carbon into a laser cut diamond surface, [9,[12][13][14][15][16][17][18][19][20][21], unlike dry/wet etching. [22] This is attributed to thermal damage by the laser beam, resulting in a solid to solid conversion of diamond to graphite. ...
The presence of sp2 bonded carbon on a diamond or doped diamond surface, as a result of growth or processing, can affect material properties negatively, hence removal processes must be developed. Using boron doped diamond (BDD) we investigate the effectiveness of different removal methods via electrochemistry and transmission electron microscopy. We focus on two BDD surfaces, one processed by ns laser micromachining and the second which contains sp2 bonded carbon as a result of chemical vapour deposition (CVD) growth. After micromachining a layer of ordered graphite sits on the BDD surface, topped by fissured amorphous carbon (total thickness ~ m). Oxidative acid treatment at elevated temperature cannot remove all the sp2 bonded carbon and much smaller clusters of perpendicularly-orientated graphite (10’s nm), capped with a thinner layer of amorphous carbon – that we term “denatured graphite” – remain. In contrast, thermal oxidation in air at 600 oC is capable of all cluster removal, and can also be used to remove sp2 bonded carbon from CVD-grown BDD. Such understanding is important to any application where sp2 bonded carbon resulting from CVD growth or laser processing is detrimental for the intended application, e.g. in diamond quantum technology, photonics and electrochemistry.<br
... [5][6][7][8] The latter is extremely useful for cutting and structuring wafer scale diamond (and BDD) films into much smaller, useable geometries. [9][10][11][12] ns-laser micromachining does however, introduce non-diamond carbon into a laser cut diamond surface, [9,[12][13][14][15][16][17][18][19][20][21], unlike dry/wet etching. [22] This is attributed to thermal damage by the laser beam, resulting in a solid to solid conversion of diamond to graphite. ...
The presence of sp 2 bonded carbon on a diamond or doped diamond surface, as a result of growth or processing, can affect material properties negatively, hence removal processes must be developed. Using boron doped diamond (BDD) we investigate the effectiveness of different removal methods via electrochemistry and transmission electron microscopy. We focus on two BDD surfaces, one processed by ns laser micromachining and the second which contains sp 2 bonded carbon as a result of chemical vapour deposition (CVD) growth. After micromachining a layer of ordered graphite sits on the BDD surface, topped by fissured amorphous carbon (total thickness ~ m). Oxidative acid treatment at elevated temperature cannot remove all the sp 2 bonded carbon and much smaller clusters of perpendicularly-orientated graphite (10's nm), capped with a thinner layer of amorphous carbon-that we term "denatured graphite"-remain. In contrast, thermal oxidation in air at 600 o C is capable of all cluster removal, and can also be used to remove sp 2 bonded carbon from CVD-grown BDD. Such understanding is important to any application where sp 2 bonded carbon resulting from CVD growth or laser processing is detrimental for the intended application, e.g. in diamond quantum technology, photonics and electrochemistry.
... Current flux and low cell voltage drop can be provided even in a solution with low conductivity, by the use of Solid Polymer Electrolyte (SPE), a thin film placed between cathode and anode. SPE systems have been investigated for electrochemical ozone production (Arihara et al., 2007;Cui et al., 2009;Da Silva et al., 2010;Diniz et al., 2003;Honda et al., 2013;Okada and Naya, 2009), while they have been only barely explored as wastewater remediation technologies (Clematis et al., 2017;Grimm et al., 2000;Houk et al., 1998;Klidi et al., 2019;Simond and Comninellis, 1997). ...
Terbuthylazine (TBA) has replaced atrazine in many EU countries, becoming one of the most frequently detected pesticides in natural waters. TBA is a compound of emerging concern, due to its persistence, toxicity and proven endocrine disruption activity to wildlife and humans. Techniques applied in water treatment plants remove only partially this herbicide and poor attention is given to the generation and fate of by-products, although some of them have demonstrated an estrogenic activity comparable to atrazine. This paper summarizes the environmental occurrence of TBA and its main metabolite desethylterbuthylazine and reports the performance of an innovative electrochemical cell equipped with a solid polymer electrolyte (SPE) sandwiched between a Ti/RuO2 cathode and a Boron-Doped Diamond anode, operating at constant current, in the treatment of an aqueous solution of TBA. The herbicide removal in the first 30 min of treatment increases from 42% to 92% as the applied current is increased from 100 to 500 mA. The rate of degradation at 500 mA decreases between 30 and 60 min, with a final abatement of 97%. An 89% removal was reached at 100 mA when the initial TBA concentration was raised from 0.1 to 4 mg L−1 and less than 1% of the herbicide was converted in desethylterbuthylazine and minor metabolites. No chemicals are needed, no sludge is produced. Further research is encouraged, as this technology may be promising for the achievement of a zero-discharge removal of different emerging pollutants as pesticides, pharmaceuticals and personal care products.
... 6 There are two materials capable of current efficiencies of ≥ 20%: boron doped diamond (BDD) and Ni and Sb-codoped SnO2. 4 BDD anodes have been employed to generate O3 in PEM-based, electrolyte-free water at current efficiencies up to 47% and current densities up to 530 mA cm -2 . [7][8][9] However, the cell voltages required with such systems are high, and it is not at all clear that BDD anodes can be expected to produce ozone routinely as they are more usually associated with the direct oxidation of organics. ...
This paper reports a systematic study of the codoping of SnO2with Sb and Ni to identify the mechanism responsible for the electrocatalytic generation of ozone on Ni/Sb-SnO2. On the basis of interpretation of a combination of X-ray diffraction, BET surface area measurements (N2), and thermal analysis, the formation of ozone appears to take place on particle surfaces of composite Sb-SnO2grains and is controlled by diffusion of OH along internal crystallite surfaces within the grain. Sb-doped SnO2is inactive with respect to ozone evolution in the absence of Ni, demonstrating a synergic interaction between nickel and antimony. From X-ray photoelectron spectroscopy (XPS) investigations, Sb(V) ions substitute for Sn(IV) in the lattice with a preference for centrosymmetric coordination sites, while the Sb(III) ions occur at grain surfaces or boundaries. Ni was not detected by XPS, being located in the subsurface region at concentrations below the detection limit of the instrument. In addition to identification of a possible mechanism for ozone formation, the study resulted in the production of active nanopowders which will allow the fabrication of high-surface-area anodes with the potential to exceed the space-time yields of β-PbO2anodes, permitting the application the Ni/Sb-SnO2anodes in the treatment of real waters.
... Both these factors can be improved by the choice of a better electrocatalyst on the anode. Several anode materials have been studied for ozone generation such as platinum, 5 PbO 2 , 6 Si/TiO x /Pt/TiO x , 7 boron doped diamond (BDD) 8 and Pt/TiO x . 9 Wang et al. in 2005 reported a metal mixed oxide of Sn-Sb-Ni oxide as an anode that shows current efficiencies for ozone of up to 35% in acidic electrolyte at room temperature. ...
A novel three-layer anode having the composition Ti/TiH x /Ni-Sb-SnO 2 (Ti/TiH x /NATO) was successfully prepared by a spin-coating and pyrolysis process aiming at a long service lifetime and good electrocatalytic properties for ozone formation. The TiH x as an interlayer was produced by electrochemical cathodic reduction of a coated layer of the TiO x on the titanium substrate. Spin coating and thermal decomposition were used to deposit the Sn-Sb-Ni precursor on the surface of the prepared Ti/TiH x electrode. Cyclic and linear scanning voltammetry, Raman spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to reveal the electrode performance and morphology. Results show that the onset potential for the oxygen evolution reaction (OER) of Ti/TiH x /NATO is higher than for Ti/NATO. They also indicate that the service lifetime of the Ti/TiH x /NATO is twice as long as the Ti/NATO at a current density of 50 mA.cm −2 at room temperature. Electrochemical ozone generation and degradation of the methylene blue were investigated to confirm selectivity and activity of the electrodes. After 5 min electrolysis, a current efficiency for ozone generation of 56% was obtained the electrode with TiH x while 38% was obtained on Ti/NATO under same conditions. The results also confirm that the Ti/TiH x /NATO has a higher kinetic rate constant and decolorization efficiency for removal of the methylene blue compare to the Ti/NATO. The rate constant for the pseudo-first ordered reaction of methylene blue degradation showed high values of 350 × 10 −3 min −1 for Ti/NATO and 440 × 10 −3 min −1 for Ti/TiH x /NATO. Nowadays, ozone is considered an environmentally friendly oxidant-disinfectant agent with multiple possible applications in medicine, chemical synthesis, disinfection, water and wastewater treatment and pulp and paper bleaching. 1-3 Ozone is commonly produced by the Cold Corona Discharge (CCD) technology, but can also be produced by electrolysis. The electrochemical oxidation process has several advantages over CCD, since a higher ozone concentration is obtained in both liquid and gas phase and there is no need for gas feed and no NO x by-product formation. 4 A disadvantage with the electrolytic process is the higher energy consumption due to its low current efficiency for ozone generation and high anode potential resulting in a high cell voltage. Both these factors can be improved by the choice of a better electrocatalyst on the anode. Several anode materials have been studied for ozone generation such as platinum, 5 PbO 2 , 6 Si/TiO x /Pt/TiO x , 7 boron doped diamond (BDD) 8 and Pt/TiO x. 9 Wang et al. in 2005 reported a metal mixed oxide of Sn-Sb-Ni oxide as an anode that shows current efficiencies for ozone of up to 35% in acidic electrolyte at room temperature. 10 The results were later confirmed by Christensen et al. in 2009 who showed current efficiencies of up to 50% in the acidic electrolyte at room temperature and at cell voltages <3 V. 11 Remarkably high current efficiencies for ozone generation at low cell voltage were found also by others. 11-14 The titanium-based tin, antimony and nickel oxide (Ti/NATO) is a promising electrode for electrochemical ozone production due to high overpotential for the oxygen evolution reaction (OER), high conductivity and its low cost. A problem with NATO is the relatively short lifetime of the catalyst, which today is too short to allow for industrial applications. There are several processes that may cause deactivation of Ti/NATO electrodes such as dissolution of Ni 2+ at acidic conditions and therefore loss of the active sites, physical loss of catalyst due to spallation and formation of a re-sistive TiO 2 layer. 13 Most studies of the Ti/NATO have been fo-cused on finding optimal conditions for the electrode coating preparation procedure, to achieve high current efficiencies for ozone generation. In recent years, the effect of an interlayer and of doping of different materials on the stability and electrocatalytic activity of SnO 2 based electrode has been studied by several researchers. 13-20 Li et al. z (2013) investigated the influence of fluoride-doped tin oxide (FTO) as an interlayer on the performance of a Ti/NATO electrode. Their results indicated that the electrode surface was smoother with FTO as an interlayer while the crystallite size was reduced. They also investigated the stability of the electrode in accelerated lifetime tests. The service lifetime of the electrode with FTO was 275 min, which was six times longer than without the interlayer electrode measured in 0.5 M Na 2 SO 4 solution at a current density of 500 mA.cm −2. 21 In 2014, Shao et al. improved the stability of the Ti/Sb-SnO 2 electrode by introducing Sb-SnO 2 via an electrodeposition method, as an interlayer between the substrate and the outer Sb-SnO 2 layer which was coated using a brushing method. Their result showed that the electrode with Sb-SnO 2 as interlayer was compact and crack-free and the accelerated life time of the electrode with interlayer was 10.71h which was much higher than that of the electrode without interlayer (0.84 h) measured in a 0.5 M H 2 SO 4 solution at a current density of 200 mA.cm −2. 22 Wu et al. (2015) reported the fabrication of a polytetrafluoroethylene (PTFE) Sb-doped SnO 2 composite electrode with nanotubes of titanium (NTs) as an interlayer, which was produced using pulse elec-trodeposition. Their results showed an accelerated lifetime of TiO 2-NTs/SnO 2-Sb-PTFE up to 16 times longer than that of a conventional TiO 2 /SnO 2-Sb electrode. 23 Shao et al. (2014 and 2016) introduced TiH x as an interlayer to improve the stability and the electrochemical properties of a Ti/Sb-SnO 2 electrode. It was fabricated using dip coating and electrodeposition. Their results showed that the electrode with interlayer has better stability, higher oxygen evolution potential and lower electron transfer resistance compared with the electrode without interlayer. They reported the accelerated lifetimes of Ti/Sb−SnO 2 and Ti/TiH x /Sb−SnO 2 , to be approximately 14 and 72 hours, respectively. 24,25 In this research, a three-layer anode Ti/TiH x /Ni-Sb-SnO 2 (NATO) electrode was prepared to enhance the stability and electrochemi-cal performance for ozone generation. To have controlled sample preparation and achieve reproducible results is of large importance. Spin coating is a rather simple technique that has proven to reproducibly yield electrodes with uniform oxide-coating thickness. 26 Two kinds of electrodes were prepared by a spin-coating and pyrolysis method. The electrochemical properties and surface properties of the electrodes were investigated and the stability of the Ti/NATO with and without TiH x as an interlayer were compared. Generation of ozone and degradation of methylene blue as an organic pollutant model were investigated to confirm the electrocatalytic activity of the electrodes.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 80.217.139.103 Downloaded on 2018-06-16 to IP
... Both these factors can be improved by the choice of a better electrocatalyst on the anode. Several anode materials have been studied for ozone generation such as platinum, 5 PbO 2 , 6 Si/TiO x /Pt/TiO x , 7 boron doped diamond (BDD) 8 and Pt/TiO x . 9 Wang et al. in 2005 reported a metal mixed oxide of Sn-Sb-Ni oxide as an anode that shows current efficiencies for ozone of up to 35% in acidic electrolyte at room temperature. ...
A novel three-layer anode having the composition Ti/TiHx/Ni-Sb-SnO2 (Ti/TiHx/NATO) was successfully prepared by a spin-coating and pyrolysis process aiming at a long service lifetime and good electrocatalytic properties for ozone formation. The TiHx as an interlayer was produced by electrochemical cathodic reduction of a coated layer of the TiOx on the titanium substrate. Spin coating and thermal decomposition were used to deposit the Sn-Sb-Ni precursor on the surface of the prepared Ti/TiHx electrode. Cyclic and linear scanning voltammetry, Raman spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to reveal the electrode performance and morphology. Results show that the onset potential for the oxygen evolution reaction (OER) of Ti/TiHx/NATO is higher than for Ti/NATO. They also indicate that the service lifetime of the Ti/TiHx/NATO is twice as long as the Ti/NATO at a current density of 50 mA.cm−² at room temperature. Electrochemical ozone generation and degradation of the methylene blue were investigated to confirm selectivity and activity of the electrodes. After 5 min electrolysis, a current efficiency for ozone generation of 56% was obtained the electrode with TiHx while 38% was obtained on Ti/NATO under same conditions. The results also confirm that the Ti/TiHx/NATO has a higher kinetic rate constant and decolorization efficiency for removal of the methylene blue compare to the Ti/NATO. The rate constant for the pseudo-first ordered reaction of methylene blue degradation showed high values of 350 × 10−³ min−¹ for Ti/NATO and 440 × 10−³ min−¹ for Ti/TiHx/NATO.
... Possible drawbacks of its employment are the cost of membrane and possible formation of fouling. Currently, in electrochemical industry, solid polymer is especially employed to produce ozone [18][19][20][21][22][23][24] but it can be effectively used in electrochemical processes for wastewaters treatment [25][26][27][28]. ...
This paper explores the applicability of an innovative electrochemical cell with a solid polymer electrolyte (SPE) with mesh electrodes for the electrochemical oxidation of a low conductivity solution (0.022 mS/cm) containing crystal violet (CV) dye compound as model pollutant in a range concentration of 25–100 mg/L. The system anode/membrane/cathode is formed by Nafion membrane sandwiched between a Ti/RuO2 cathode and a BDD anode. The dependence of applied current, stirring rate, supporting electrolyte and temperature has been investigated. The experimental results showed that the electrochemical cell with SPE is suitable for the treatment of solution with a very low conductivity since the CV solution was completely mineralized with an energy consumption of about 60 kWh m⁻³. Furthermore, the process was under charge transfer control for low applied current, becoming mass transfer control around 1 A. The addition of supporting electrolyte as Na2SO4 (0.6 and 1 g/L) and NaHCO3 (1 g/L) to the solution decreased the removal rate due to the presence of competitive reaction and scavengers media. The evolution of nitrogen compounds during the electrolysis shows that at the end of the process the 80% of initial N has been converted in nitrate and ammonium, indicating the formation of volatile compound.
... In addition to the use of the oxide electrodes, a special attention in the last two decades was given for the 'inert' electrode material denoted as boron-doped diamond (BDD) [28], which exhibits outstanding performance for the electrochemical incineration of organic pollutants. However, some drawbacks exist in the case of BDD, which are mainly concerned with high-fabrication costs and the difficult preparation of compact thin BDD films onto porous metallic substrates [29]. ...
A mixed oxide-covered mesh electrode composed of NiCo2O4 (MOME-NiCo2O4) was prepared on a stainless-steel substrate using thermal decomposition (slow-cooling rate method). Surface, bulk and electrochemical properties of MOME were studied using different techniques, namely scanning electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry (CV) with determination of the electrochemical porosity (ϕ) and morphology factor (φ) parameters, quasi-stationary polarisation curves (PC) and electrochemical impedance spectroscopy (EIS). SEM images revealed a good coverage of the metallic wires by a compact oxide layer (absence of cracks). XRD analysis confirmed the formation of the spinel NiCo2O4 with the presence of NiO. The ‘in situ’ surface parameters denoted as ϕ and φ exhibited values of 0.39 and 0.33, respectively, revealing that the electrochemically active surface area is mainly confined to the ‘outer/external’ surface regions of the oxide layer. The PC was characterised by two Tafel slopes distributed in the low (b1 = 46 mV dec−1) and high (b2 = 59 mV dec−1) overpotential domains. The corresponding apparent exchange current densities were j0(1) = (3.43 ± 0.11) × 10−6 A cm−2 and j0(2) = (6.70 ± 0.08) × 10−6 A cm−2, respectively. The EIS study accomplished in the low-overpotential domain revealed a Tafel slope (b1) of 51 mV dec−1. According to the spin-trapping reaction using N,N-dimethyl-p-nitrosoaniline (RNO), the MOME-NiCo2O4 electrode exhibited good performance for the generation of weakly adsorbed hydroxyl radicals (HO•) during the OER in electrolyte-free water.
... 24,25 Another interesting application of BDD is the electrochemical ozone production (EOP) by direct water electrolysis for application in pure water systems. [26][27][28] In the EOP process, the electrolytic cell is constructed by sandwiching a Nafion film between two flat BDD-coated expanded metal electrodes or between two freestanding perforated diamonds (Fig. 4). ...
... It increases the electrolyte conductivity that is favorable for ozone production. However, high concentration of electrolyte can inactivate the reaction sites on the surface of the electrode and consequently decrease ozone generation [6]. So, the optimization algorithm increases electrolyte concentration to a medium level (namely below 0.5 M) and keeps it nearly constant for increasing ozone concentration (Fig. 7c). ...
In this paper, simultaneous maximization of generated ozone concentration and minimization of electrical energy consumption is investigated in a laboratory-scale electrochemical ozone production system (EOP). Neural network simulation of EOP was carried out for generated ozone concentration prediction by Abbasi et al. (Chem Eng Res Des 92(11):2618–2625, 2014). In this study, neural network models (as black box models) were developed to predict both generated ozone concentration and electrical energy consumption. The models then were used for optimization. Altruistic non-dominated sorting genetic algorithm with jumping gene variant and termination criterion was used for MOO. Generational distance and spread were used in the termination criterion in order to stop algorithm after the right number of generations. Moreover, several optimal solutions from the Pareto-optimal set are chosen and then validated experimentally.
... 65 kWh kg À1 . However, recently Arihara et al. (2007) observed a current efficiency of 47% using a zero gap (Nafion polymer electrolyte membrane) cell and a diamond anode, at 20 C with deionized water, but the energy consumption was 130 kW hr kg À1 . In comparison, the energy requirement of CCD is often given as in the range ca. 13 kWh kg À1 to 29 kWh kg À1 (Seidel, 2004); although the requirement for the most recent commercial systems has been quoted as being as low as 8 kWh kg À1 (Rau, 2009). ...
The electrochemical generation of ozone by Ni/Sb-SnO2 anodes immersed in 0.5M H2SO4 was assessed in both flow and recycle systems using the same electrochemical cell. The anodes were found to exhibit current efficiencies of up to 50% for ozone generation under flow conditions at room temperature, with an optimum mole ratio in the precursor solutions of ca. 500:8:3 Sn:Sb:Ni and optimum cell voltage of 2.7V. A comparison of the data obtained under flow and recycle conditions suggests that the presence of ozone in the anolyte inhibits its formation. The minimum electrical energy cost achieved, of 18 kWh kg−1 compares favorably with estimated costs for Cold Corona Discharge generally reported in the literature, especially when the very significant advantages of electrochemical ozone generation are taken into account.
... 10 The traditional method of generating O 3 is via a cold corona discharge reactor which occurs via the following reaction: A more promising method is to produce O 3 via the electrochemical process of water splitting known as electrochemical ozone production (EOP). This is not a new process with previous work being carried out on various different anodes such as Pt, 13,14 b-PbO 2 , [15][16][17] BDD 18,19 and Ni/Sb-SnO 2 20-22 anode materials. The electrochemical splitting of water can occur through either a 4 or 6 step electron process shown in reactions (2) and (3): ...
The H2O splitting mechanism is a very attractive alternative used in electrochemistry for the formation of O3. The most efficient catalysts employed for this reaction at room temperature are SnO2-based, in particular the Ni/Sb-SnO2 catalyst. In order to investigate the H2O splitting mechanism density functional theory (DFT) was performed on a Ni/Sb-SnO2 surface with oxygen vacancies. By calculating different SnO2 facets, the (110) facet was deemed most stable, and further doped with Sb and Ni. On this surface, the H2O splitting mechanism was modelled paying particular attention to the final two steps, the formation of O2 and O3. Previous studies on β-PbO2 have shown that the final step in the reaction (the formation of O3) occurs via an Eley-Rideal style interaction where surface O2 desorbs before attacking surface O to form O3. It is revealed that for Ni/Sb-SnO2, although the overall reaction is the same the surface mechanism is different. The formation of O3 is found to occur through a Langmuir-Hinshelwood mechanism as opposed to the Eley-Rideal mechanism. In addition to this the relevant adsorption energies (Eads), Gibb's free energy (ΔGrxn) and activation barriers (Eact) for the final two steps modelled in the gas phase have been shown, providing the basis for a tool to develop new materials with higher current efficiencies.
... The last is an interesting technological development which comprises a solid thin film electrolyte sandwiched between cathode and anode, allowing current flux with a low cell voltage even in a solution with low conductivity. A SPE system is used commercially for the electrochemical production of ozone [10][11][12][13][14][15][16] and it is also a promising approach for wastewater treatment but, to the best of our knowledge, this application has not been explored in any depth [17][18][19]. ...
... Porous platinum typically serves as the cathode. Various anode materials have been used and currently boron-doped diamond electrodes (BDD) are being most intensively studied [152,153], but PbO 2 is the current state-of-the-art [154]. The standard electrode reaction potential of ozone formation (Eq. (6)) is 280 mV higher compared with the formation of oxygen. ...
This review is devoted to membrane electrolysis, in particular utilizing ion-selective membranes, as an important part of both existing and emerging industrial electrochemical processes. It aims to provide fundamental information on the history and development, current status and future perspectives of membrane electrolysis. It aims to provide fundamental information on the history and development, current status and future perspectives of membrane electrolysis. An overview of the history of electromembrane processes is given with the focus on brine electrolysis since it is the predominant electrochemical industrial technology utilizing ion-selective membranes. This is followed by a summary of the wide range of hydrogen-based energy conversion processes with different degrees of maturity, i.e. water electrolysis and fuel cells, which promise to become the next generation of major electromembrane processes. The overview of the state-of-the-art is rounded off by a number of smaller-scale processes utilizing ionically conducting solid electrolytes and ion-selective membranes that are already commercially available. The article concludes by considering potential future developments in this exciting field of electrochemistry.
... Recently, remarkable high current efficiencies (up to 50%) have been reported by some researches using a recycled flow in the structure of applied ozone generator electrochemical cells (Arihara et al., 2007;Basiriparsa and Abbasi, 2012;Wang et al., 2006). Now in this work, the feasibility of application of a homemade type of these ozone generators consist of an effective Ti/Sn-Sb-Ni anode is studied in an ozonation process. ...
An ozonation process was performed using a recycled electrochemical ozone generator system. A titanium based electrode, coated with nanocomposite of Sn-Sb-Ni was applied as anode in a laboratory-made electrochemical reactor. A constant flow rate of 192 mg/h of generated ozone was entered to an ozonation reactor to contact with a typical target pollutant, i.e., Rhodamine B (Rh.B) molecules in aqueous solution. Four operational parameters such as: initial dye concentration, pH, temperature and the contact time were evaluated for the ozonation process. Experimental findings revealed that for a solution of 8 mg/L of the dye, the degradation efficiency could reach to 99.5% after 30 min at pH 3.7 and temperature of 45 °C as the optimum conditions. Kinetic studies showed that a second order equation can describe the ozonation adequately well under different temperatures. Also, considering to the importance of process simulation, a three-layered feed forward back propagation artificial neural network model was developed. Sensitivity analysis indicated order of the operational parameter's relative importance on the model output as: time ≫ pH > Rh . B initial concentration > temperature.
This study valorized scanning electrochemical microscopy (SECM) for the detection of dissolved O3, which is increasingly in demand for water treatment. Au ultramicroelectrodes biased at 0.62 V RHE provided superior activity and selectivity for O3 reduction, compared to Pt analogues. It allowed quantitative in situ interrogation of ozone evolution reaction (OZER) electrocatalysts with unprecedented estimations on the OZER overpotential. The difference in onset potentials between the OZER and the competing oxygen evolution reaction (OER) primarily accounted for the OZER current efficiency (CE) on boron-doped diamond (BDD, 1.4% at 10 mA cm-2 in 0.5 M H2SO4), Ni-Sb-doped SnO2 (NSS, 10.8%), and SiOx-coated NSS (NSS/SiOx, 34.4%). SECM areal scans in tandem with elemental mapping perspicuously visualized the improved OZER activity by the SiOx overlayer on NSS. A shift in the charge transfer coefficient further rationalized the elevated OZER selectivity on NSS/SiOx, in association with the weakened Sn-O bond strength confirmed by valence band X-ray photoelectron spectra. The invigorated OZER on NSS/SiOx effectively accelerated the degradation of a model aqueous pollutant (4-chlorophenol).
Recently, electrochemical generation of hydrogen peroxide (H2O2) using cathodic oxygen reduction reaction (ORR) has been conventionally implemented in electrochemical advanced oxidation processes (EAOPs) for water treatment. H2O2 could be activated using reagents like Fe²⁺ and O3 to produce the hydroxyl radicals (•OH), and further reduce organics. The conventional Fenton, Peroxone and Electro-Oxidation (EO) processes were enhanced using H2O2 generation cathode to execute Electro-Fenton, Electro-Peroxone and ORR-EO processes. In this study, the carbon-based materials as catalysts for H2O2 generation cathode were generally investigated. The development of cutting-edge EAOPs based on H2O2 generation cathode was introduced using three stories. The future viewpoint of EAOPs based on H2O2 generation cathode was discussed.
Electrochemical ozone production (EOP) is an attractive technology for disinfection and sterilization purposes. This work reports a study on the EOP performance of the solid polymer electrolyte (SPE) electrolyzer, including the optimization of electrode configuration and operation conditions. It is proven that the EOP performance is highly affected by electrode configuration. Tests using BDDs with different B/C ratios demonstrate that BDD-4.9 provides more reaction sites and faster electron transfer rate, exhibiting a high electrocatalytic activity for EOP. Regarding electrode thickness, 0.54 mm in thickness is the most suitable for the EOP from the perspective of less power consumption. Moreover, operation conditions were evaluated. It was found that increasing water flow rate is an effective strategy for promoting ozone dissolution, and within the present experimental range, the water flow rate of 63 L·h−1 was identified. Meanwhile, through the study of all processes occurring inside the electrolyzer at higher current densities, the optimum current density was determined to be 125 mA·cm−2. Based on these results, ozone water presents excellent performance in the killing of Escherichia coli with high inoculum concentrations, indicating potential application performance in the field of environment. HIGHLIGHTS
Ozone production by electrochemical technology.;
The SPE electrolyzer with specially designed clamping system served as the ozone reactor.;
Using a boron-doped diamond (BDD) as the electrode material.;
The SPE electrolyzer can continuously and effectively produce ozone by a flow-through system with low energy consumption.;
Ozone water shows a considerable bactericidal effect on different concentrations of E. coli.;
In this study, it was investigated the capability of new generation Sb-SnO2/Ti anodes, which are well known with their promising results in ozone generation and stability, to remove cefuroxime (CXM) antibiotic from aqueous solution. Comparison of different electrolyte types were performed for this purpose; NaCl and KCl. KCl increased the conductivity and caused to the formation of important oxidants and thus, affected electrochemical oxidation reactions more positively than NaCl. It was obtained that, pH parameter has a very important effect on the removal efficiencies in this process and higher efficiencies were obtained at the natural pH value (pH 7) of the aqueous solution. It was thought that, this was probably because the reactions occurred in aqueous solution mostly instead of anodic surface. Furthermore, the removal efficiencies increased with current density increase and the best results were obtained at 50 mA/cm2 current density. As a result of the study, at the end of 60 min of reaction, the aqueous solution containing cefuroxime antibiotic was completely treated without any toxic intermediate product formation with 750 mg/L KCl addition, at pH 7 and 50 mA/cm2 current density.
The boron-doped diamond (BDD) electrode, having ultra-high oxygen evolution potential and anodic stability, is potentially considered the ideal candidate for the next-generation ozone generator despite the relatively low current efficiency. In this work, we first report using a microporous BDD electrode etched by oxygen plasma, denoted as p-BDD, to improve the performance of electrochemical ozone generation. Two parameters, including O2 plasma etching temperature and time, are experimentally optimized. We demonstrated that the electrochemically active surface area (ECSA) of the optimal p-BDD is 2.51 times that of the bare BDD, and this p-BDD shows about one-quarter lower charge transfer resistance than the latter. Under the same unit energy consumption, the p-BDD has 3.76 times the ozone generation capacity compared to the latter. The p-BDD shows excellent long-term stability, only having 4.2% of the decrease in the current density up to 40 h of consecutive water electrolysis under the steady-state period, and it also remains a 100% recovery rate in its capability of electrochemical performance after mild treatment by cycling at a diluted sulfuric acid solution for 200 s
In this study, several titanium-based electrodes (e.g., Ti, Ti/SnO2–Sb–Ni, Ti/SnO2–Sb–Ni-MWCNTs, Ti/TiHx/SnO2–Sb–Ni and Ti/TiHx/SnO2–Sb–Ni-MWCNTs) were fabricated by spin-coating and pyrolysis methods for electrochemical ozone generation. The modified electrodes were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) techniques. These electrodes are used as an anode for electrochemical ozone generation. The ozone generation at the surface of the electrodes was investigated. The optimum molar ratio of metal salts and multi-walled carbon nanotubes (MWCNTs) (Sn/ Sb/ Ni/ MWCNTs) was obtained 500:8:1:15. The repetition coating time, electrolysis time, electrolysis current density and kind of electrolytes (H3PO4, HClO4 and H2SO4) at different concentrations (0.1, 0.05, 0.1, 0.2, 0.5 and 1 M) were investigated and, respectively, were determined (i.e., 22 times, 120 s, 20 mA cm⁻², HClO4 and 0.1 M). As the results showed, in 4 mL HClO4 (0.1 M) after 25 min electrolysis under a constant current of 12.8 mA, at the surface of the Ti/TiHx/SnO2–Sb–Ni-MWCNTs electrode (A = 0.64 cm²) could produce 19.9 mg L⁻¹ of ozone, which is triple the amount produced by the electrodes not modified with MWCNTs. Also, the best-modified electrode (Ti/TiHx/SnO2–Sb–Ni-MWCNTs) was used for electrooxidation of three types of disperse dyes. The results showed that Ti/TiHx/SnO2–Sb–Ni-MWCNTs electrode can remove the dye (100 mg L⁻¹) molecules up to 97%, 90% and 86% for C.I. Disperse yellow 54 (DY 54), C.I. Disperse blue 198 (DB 198) and C.I. Disperse red 167 (DR 167), respectively.
Graphic abstract
Water pollution control and the development of clean technologies for water, air and soil treatments comprise one of the most important challenges for modern society. Ozone is known as a strong and clean oxidizing agent that can be used for water and wastewater treatment. In this research, a novel Ti/TiHx/SnO2-Sb2O5-NiO-CNT modified titanium electrode containing carbon nanotubes (CNT) was fabricated for in-situ ozone generation. The electrode was characterized using SEM, XRD and LSV techniques. CNT presence caused an increase in ozone generation efficiency leading to the higher concentrations of dissolved ozone in water compared to the recently reported researchers. Ozone generation at the surface of the electrode was determined using the standard indigo method. Electrochemical ozone was further used in degradation of C.I. Reactive red 195 (RR 195). It was found that the modified electrode could degrade 96% of RR 195 from initial concentration of 300 mg∙L<sup>-1</sup> in 30 min under current density of 20 mA∙cm<sup>-2</sup>. COD removal was also measured as high as 60 percent.
This mini review supplies a current opinion about the most recent works, which have been carried out toward the electrochemical treatment of organic compounds spike in low conductive solution. In particular, the first section is focused on the use of a solid polymer electrolyte in order to allow current flux with a low cell voltage even in a solution without supporting electrolyte. Meanwhile, the second section describes the microfluidic cells, that are characterized by a very small distances between electrodes (tens or few hundreds μm) that reduce the ohmic resistances and increase the mass transport of the pollutants to electrodes surfaces.
The presence of sp² bonded carbon on a diamond or doped diamond surface, as a result of growth or processing, can affect material properties negatively, hence removal processes must be developed. Using boron doped diamond (BDD) we investigate the effectiveness of different removal methods via electrochemistry and transmission electron microscopy. We focus on two BDD surfaces, one processed by ns laser micromachining and the second which contains sp² bonded carbon as a result of chemical vapour deposition (CVD) growth. After micromachining a layer of ordered graphite sits on the BDD surface, topped by fissured amorphous carbon (total thickness ∼ μm). Oxidative acid treatment at elevated temperature cannot remove all the sp² bonded carbon and much smaller clusters of perpendicularly-orientated graphite (tens of nm in diameter), capped with a thinner layer of amorphous carbon – that we term “denatured graphite” – remain. In contrast, thermal oxidation in air at 600 °C is capable of all cluster removal, and can also be used to remove sp² bonded carbon from as-grown CVD-grown BDD. Such understanding is important to any application where sp² bonded surface carbon resulting from CVD growth or laser processing is detrimental for the intended application, e.g. in diamond quantum technology, photonics and electrochemistry.
The red mud/g-C3N4 (RM-CN) composite was directly prepared via one-step thermal polymerization method using melamine and industrial waste residue (red mud) as raw materials. Under the synergistic effect of adsorption and photocatalysis, RM-CN composites have a significant effect for the removal of organic pollutants from wastewater. Compared with pure CN, the specific surface area of RM-CN has been significantly enhanced with the introduction of RM. Additionality, the optical absorption and photocurrent response exhibit obvious enhancement with respect to RM-CN as compared with that of pristine CN photocatalyst. The optimized 0.8% RM-CN product (with the RM mass content of 0.8 wt% in precursor) displayed referable photocatalytic degradation efficiency for antibiotics and dyes under visible light, as well as excellent recycle performance. This work poses a great potential in the actual wastewater treatment, and it is of great significance to the resource utilization and the cost saving of the raw material.
It is well known that “diamond” has ultra-high hardness and low electrical conductivity. However, introducing dopants such as boron into the diamond lattice during growth can increase its conductivity. Boron-doped diamond (BDD) with high conductivity is attracting increasing attention as one of the next-generation of superior electrode materials. In particular, it is expected that BDD electrodes can help solve some of our environmental problems and also improve our quality of life through their use in biomedical devices. Here, in this article, recent developments in the electrochemical applications of boron-doped diamond (BDD) electrodes are introduced.
The aim of this study was to search for performance of Pt/Ni-Sb-SnO2 and GC/Ni-Sb-SnO2 for limiting O2 evolution and enhancing ozone production. The impact of basic variables on the coated electrodes like nucleation current density, growth current density, growth charge, nucleation charge and electrolyte type were surveyed. Furthermore, the three-dimensionality the scaling ratio and the percentage of electroactive surface of the modified GC electrodes has been studied by the fractal method. The resulting data is fully consistent with the experimental results. According to the SEM images of the electrode's surface, the surface of the modified GC electrode by Sn, Sb and Ni metals has been covered. This situation did not happen completely in Pt electrode, which is indicative of the better performance of the modified GC electrode. The results of the XRD and EDX also confirming the above findings show that unlike the modified GC electrode, Sn has not been deposited on the Pt electrode's surface.
This paper reports a systematic study of the co-doping of SnO2 with Sb and Ni in order to identify the mechanisms responsible for the generation of ozone at Ni/Sb-SnO2 anodes. Based on interpretation of a combination of X-ray diffraction, BET surface area measurements (N2) and thermal analysis, the formation of ozone appears to take place on particle surfaces of composite Sb-SnO2 grains, and is controlled by diffusion of OH along internal crystallite surfaces within the grain. Sb-doped SnO2 is inactive with respect to ozone evolution in the absence of Ni, demonstrating a synergic interaction between nickel and antimony. From XPS investigations, Sb(V) ions substitute for Sn(IV) in the lattice, with a preference for centrosymmetric coordination sites whilst the Sb(III) ions occur at grain surfaces or boundaries. Ni occupies Sn(IV) sites in the subsurface region at concentrations below detection (<0.02 at.%), as Ni(II) and compensated by oxygen vacancies. Dissociation of absorbed O2 at these gives single O atoms at Sb(III) sites, reacting with absorbed hydroxyl to produce O3. In addition to identifying a possible mechanism for ozone formation, the study resulted in the production of active nanopowders which have potential for use in the fabrication of high surface-area anodes able to exceed the space-time yields of beta-PbO2 anodes, permitting the application the Ni/Sb-SnO2 anodes in the treatment of real waters.
A nanocomposite SnO2 electrode was prepared and its performance on electrochemical ozone synthesis was studied. The factors affecting ozone production and its current efficiency, such as current density, temperature, pH, supporting electrolyte and liquid flow, were investigated. The formation of hydroxyl radical was detected using trapping protocol and was compared with ozone generation. The results indicate that the ozone production increases with current density, and an optimum current density of 5 mA cm⁻² is obtained for the current efficiency of ozone generation. Lower temperature, lower pH and higher liquid flow favor ozone production as well as its current efficiency. As a supporting electrolyte, Na2SO4 appears to be more suitable than NaClO4, NaNO3 and NaCl for ozone generation on the nanocomposite SnO2 electrode. An optimum electrolyte concentration of Na2SO4 is observed to be 0.25 M, and a little bit of KPF6 addition (0.01 - 0.05 M) has an obviously positive effect on ozone generation. Current density and solution pH have a coincident effect on ozone and hydroxyl radical generation, while temperature has an inconsistent effect on ozone and hydroxyl radical generation and KPF6 addition has no effect on hydroxyl radical generation on the nanocomposite SnO2 electrode. The morphology and structure of the nanocomposite SnO2 electrode before and after accelerated life test were characterized by SEM and XRD analysis. It is suggested that the deactivation of nanocomposite SnO2 electrode is caused by the destruction of SnO2 coating film and the growth of TiO2 between Ti-base and SnO2 coating film.
Solution conductivity sensors (electrodes) are widely used in industrial and research settings to make measurements across the wide range of conductivities found in aqueous solutions, from distilled water to concentrated salts and acids. However, changes in electrode geometry as a result of mechanical wear, surface fouling or chemical attack result in changes to sensor performance, necessitating regular recalibration. Furthermore, direct contact with solution means exposed electrodes are susceptible to surface fouling or corrosion. In this paper we describe, a corrosion resistant, mechanically robust conductivity sensor fabricated from synthetically grown insulating and conducting diamond, using scalable chemical vapor deposition. In particular, using a two-step growth procedure pairs of co-planar conducting diamond band electrodes are integrated into an insulating diamond platform in a two point probe arrangement on a 10 mm × 10 mm diamond platform. The all-diamond sensor is demonstrated to be capable of determining solution conductivity over six orders of magnitude (10−1 to 105 μS cm−1). Longer term continuous measurements (two month period) show this sensor performs just as well as a commercially available sensor (four point probe arrangement). The exceptional chemical resistance of diamond is demonstrated by using the sensor to measure the conductivity of 98% sulfuric acid. In general, these measurements bode well for the development and application of synthetic all-diamond conductivity sensors over extended periods of time, in-situ and in challenging pH environments. Finally, the use of diamond also opens up high pressure/high temperature solution conductivity applications for this sensor.
This chapter focuses on the carbon materials used in the manufacture of chemicals, flow batteries, and effluent/water treatment. Some comments about the carbon structures are presented here. In organic electrosynthesis, carbons have been used as both anodes and cathodes. In parallel to chemical corrosion, there is mechanical erosion of the graphite to give graphite particles in the electrolyte. Improvement in the quality of water, both that supplied by utilities and that recycled in loop systems is an important goal. In addition, the treatment of effluents containing toxic materials or an unacceptably high chemical oxygen demand (COD) or total organic carbon (TOC) is an essential technology in the modern world. Electrochemical technology has approached these objectives in different ways. Because of the diverse mechanisms and the forcing conditions achievable in electrolytic cells, it is possible to oxidize a very wide range of organic molecules.
This chapter gives a brief review of recent developments on the applications of boron-doped diamond (BDD) electrodes. Specifically, electrochemical applications of BDD electrodes for water treatment, ozone generation, organic synthesis, and electrochemical analysis. Additionally several recent examples of recent developments for electrochemical analysis are introduced.
An extensive survey of the Docktor-Ingenieur Dissertationen of Jakob Jorissen and Klaus-R. Menschig, both originally from the Universitat Dortmund, is presented in regard to the empirical modeling of membrane chlor-alkali cells and how it can be applied to a combined zero gap/attached porous electrode layer membrane cell. Particular emphasis is placed on Menschig's work on zero gap (ZG) and attached porous electrode layer (APEL) membrane chlor-alkali cells, the first such research to appear in the open literature. Menschig developed various computer programs to characterize these ZG and APEL membrane chlor-alkali cells. He characterized these cells by using the following parameters: the current density distribution over the membrane, the species concentrations on the membrane surfaces, equivalent diffusion layer thicknesses for the mesh electrodes/current collectors and attached porous electrode layers, and the electrode overpotentiasl and equilibrium potentials using the surface concentrations for the ZG and APEL cell configurations. He used empirical equations first presented by Jörissen for gap membrane cells combined with his own experimental observations for a cell which used Nafion™ 390, a bilayer perfluorosulfonic acid membrane, to determine values for these parameters. His empirical relations describe the dependence of the flux of OH- from catholyte to anolyte as a function of catholyte caustic concentration (CO2NaOH) and the membrane potential drop as a function of catholyte caustic (CO2NaOH) and anolyte salt concentrations (cA:Nacl)- By using the experimental values for total cell potential, current density, and cell outlet concentrations with the empirical equations, Menschig calculated values for the characterizing parameters mentioned above. He used these values and other information (e.g., membrane and porous electrode layer conductivity) to predict the total cell potential for the ZG configuration. With prior knowledge of total cell potential and current efficiency for corresponding APEL and ZG cell configurations, membrane surface concentrations were derived and used in the prediction of total cell potential for a combined zero gap/attached electrode cell.
Several aspects of electrochemical ozone production (EOP) on β-PbO 2 were inves-tigated. The morphology of the electrode material was determined in situ using extensive (total, external, and internal differential capacity) and intensive parameters (the morphology factor, ϕ) permitting comparison with results of other laboratories if appropriate electrode characterization parameters are available. The influence of the nature of the supporting elec-trolyte on the oxygen evolution reaction (OER)/EOP processes was investigated using polar-ization curves, recorded under quasi-stationary conditions, point-by-point polarization, and chronopotentiometry. The performance of the several β-PbO 2 /electrolyte system was evalu-ated using the apparent specific power criterion. A detailed mechanism for EOP is proposed.
After an introductory discussion emphasising the importance of electrochemistry for the so-called Green Chemical Processes, the article presents a short discussion of the classical ozone generation technologies. Next a revision of the electrochemical ozone production technology focusing on such aspects as: fundamentals, latest advances, advantages and limitations of this technology is presented. Recent results about fundamentals of electrochemical ozone production obtained in our laboratory, using different electrode materials (e.g. boron doped diamond electrodes, lead dioxide and DSAÒ-based electrodes) also are presented. Different chemical processes of interest to the solution of environmental problems involving ozone are discussed.
Anodic electrodes for ozone generation were prepared with lead dioxide particles of various diameters. The lead dioxide particles were characterized with X-ray diffraction analysis, and the electrodes were characterized and performed for ozone generation. It was revealed that both the diameters of the lead dioxide particles and the contents of the pore forming agent have great effect on the performance of the electrodes. With decreasing of the diameters of the lead dioxide particles from the range of 55-74 urn to the range of 15-35 μm, the performance of the electrodes improved. But no further improvement was found with further decreasing of the particle diameters to the range of 5-15 μm. However, by employing an appropriate amount of pore forming agent during the electrode preparations, the performance of the anodic electrode can be improved. The optimized weight ratio of ammonium oxalate to lead dioxide is 1.33/100.
Thin diamond films formed on Si substrates were electrolyzed in terms of the characteristics of their electrolysis in acidic solution for testing of the possibility of their use in industrial electrochemistry. It was found that boron doped diamond anodes (100, 1000 ppm) can be operated under conditions of severe polarization, with a current density of 10 A/cm2 in a sulfuric acid solution. It was also found that ozone gas is stably generated from boron doped diamond anodes at high current densities of over 1 A/cm2. This reveals that diamond electrodes can be used in various types of industrial electrolysis.
The formation of O2/O3 on PbO2 from the electrolysis of water in neutral solutions is shown here to present some analogies and some differences with respect to the same process in acid media. The electrolyte composition affects the current efficiency for O3 formation (n) and the cell potential (E) of a Membrel type electrochemical assembly. An improvement in n and a decrease in E is observed upon addition of relatively low amounts of Na2SO4 or NaClO4 in pure water. We observe no effect of NaNO3 on either parameters. In agreement with literature data in acid solutions, F- causes an increase in both n and E. The results of electrochemical kinetic investigations with electrodes of PbO2 electrodeposited on Ti confirm the above data. Current-potential curves constructed from measurements in NaNO3 show a region of Tafel linearity with slopes of 2RT/F and RT/F in the low and high currents range, respectively. Addition of Na2SO4 and NaClO4 to NaNO3 has an effect on the process at more positive potentials only: the RT/F slope decreases toward a value of RT/2F as the concentration of the "foreign" salt is increased. As an explanation of the observed behaviour, the possibility is advanced that a step following the discharge of water is rate determining at high positive potentials with the adsorption of intermediates described by Temkin conditions. The composition of the electrolyte is expected to influence the yield of ozone formation by affecting the coverage and free energy of adsorbed oxygen intermediates.
Recently, ozone is used for many purposes as an environmentally friendly oxidant. An ozone production device with high ozone concentration and low production energy is therefore desired. One candidate for such a device is ozone water production in a water electrolysis cell using a solid polymer electrolyte with PbO2 anode catalyst. Such a device would have the advantages of being compact and producing high-concentration ozone water directly through deionized water electrolysis. We have studied ozone water production with different electrode and electrolyte compositions and operation conditions, with the aim of improving ozone production performance. The two electrolytes tested were Nafion 117 and a membrane electrode assembly (MEA) with Pt catalyst on the cathode side of Nafion 117. The two electrodes tested were a single layer of Ti expanded metal and four layers of Ti-expanded metal with different meshes. Ozone water production tests were performed for many hours with changes in temperature, water flow rate, current density, current interruption time, and other factors to optimize experimental conditions. The voltage-current characteristics of water electrolysis cell were improved significantly when the electrode was four layers of Ti-expanded metal and the electrolyte was MEA with Pt catalyst on the cathode. Stable ozone water concentration was obtained after the cell had been operated for about 8 h. The optimum temperature, water flow rate, and current density for ozone water production are 25-30 degrees C, 33 L/h, and 1.0 A/cm(2), respectively. Further, the noninterrupted supply of small current suppressed the performance deterioration of ozone water production by current interruption, and the ozone production energy was reduced by supply of oxygen to the cathode. (c) 2005 The Electrochemical Society.
Thin, boron‐doped diamond films formed on a silicon substrate were evaluated during water electrolysis in acidic solution in order to determine their potential for industrial use. Though the electrode exhibited overvoltages in excess of 2 V in the industrial current range, ozone gas was produced at a current efficiency of a few percent at ambient temperature. It was confirmed that the consumption rate of the highly doped sample was small and comparable with a platinum‐plated anode, indicating that the diamond is dimensionally stable under extreme conditions. The failure mechanism in the test is discussed on the basis of scanning electron microscopy, X‐ray diffraction, and Raman analyses. The spalling of the film from the substrate, which was observed in the deteriorated sample after the electrolysis, is attributed to the residual stress that accumulated during the production process carried out under high temperature.
Deionized water was oxidized to ozone and oxygen at the anode in a proton exchange membrane electrochemical flow reactor. The optimum conditions for ozone generation were determined as a function of the applied voltage, electrode materials (lead dioxide powders obtained from two different commercial vendors), catalyst loadings, and reactant flow rates. Measured and calculated quantities included cell current, liquid- and gas-phase ozone concentrations, and current efficiency.
The application of solid polymer electrolyte or Membrel water electrolysis cells with anodes for anodic generation of ozone in electrolyte‐free water is reported. Maximum yields were obtained at a temperature of 25°–30°C and a current density of 1.0–1.3 Acm⁻². The current efficiency was not found to depend on ozone concentration in the feed water. Both, the perfluorinated membrane and the anode do not show any degradation of performance after 2500h of operation. The excellent stability and performance of the cell are correlated with properties of the membrane and its interface with the anode: exclusive transference of electric current by protons; absence of convection in the electrolyte; high oxygen oversaturation in the vicinity of the electrode.
The application of diamond electrodes is promising for electrolyzing water to produce ozone because of their superior chemical and dimensional stability, as well as their large overpotential for the oxygen evolution reaction. A freestanding conductive diamond plate was perforated to prepare a freestanding perforated diamond electrode, which was incorporated into a zero-gap electrolytic cell for direct electrochemical ozone-water production. This system has many advantages, in particular, that it exhibits the highest current efficiency (29%) reported for the electrochemical ozone-water production thus far.
Deionized water was oxidized to form ozone at the anode while oxygen was reduced to hydrogen peroxide at the cathode in a
proton‐exchange‐membrane electrochemical flow reactor. The conditions for simultaneous generation of these oxidants were determined
as a function of the applied voltage, electrode materials (lead dioxide for ozone evolution; gold, carbon, or graphite for
peroxide evolution), and electrode configurations. Measured and calculated quantities included cell current, liquid‐ and gas‐phase
ozone concentrations, hydrogen peroxide concentrations, current efficiency for ozone and peroxide evolution, and ozone and
peroxide production rates. An applied potential of 4.5 V resulted in a current density of 2 A/cm2, yielding maximum gas‐ and liquid‐phase ozone concentrations of 60 and 3.1 mg/liter at the anode (4.5% current efficiency)
and hydrogen peroxide concentrations between 3 and 5 mg/liter at the cathode (0.8% current efficiency).
Ozone may be obtained in relatively high yield by the electrolysis of acidic aqueous solutions with β-lead dioxide anodes. The anionic coverage of the β-PbO2 electrode surface has a strong influence on the ozone current efficiencies obtained; phosphorous-32 radiotracer measurements have demonstrated that, where anion coverage of the PbO2 anode surface is high, ozone current efficiencies are low. Anionic adsorption on PbO2 at ozone evolution potentials is so persistent that the polarization history of the anode determines its subsequent behavior with respect to ozone formation. Such a conclusion lead to adjusting the adsorptivity of PbO2 for electrolyte anions through reduction of surface lead to oxygen stoichiometry. By so adjusting the adsorptivity, it is shown that one may alter ozone current efficiencies substantially. It is speculated that anionic coverage acts to weaken the free energy of adsorption of oxygen, and it is through such an influence that the formation of ozone is affected.
The performance of a novel electrolytic ozone generator using a solid polymer electrolyte and a PbO2 anode is described. The operating parameters studied were: current density, water flow, temperature and pressure. Optimum current yields in the order of 20% are reached with a 30 cm2 cell at a current of 40 A, a temperature of 30C and a volume feed rate of water >301 h–1. The system pressure does not influence the current efficiency or the cell voltage. The specific power consumption of a state-of-the-art cell is in the order of 65 W h g–1. The technique has been applied commercially in the field of disinfection of purified water for more than 3 years.
Electrolysis of water by use of a simple solid polymer electrolyte sandwich with diamond anode, Nafion® polymer electrolyte and diamond cathode leads to efficient ozone production. The dependence of ozone production rate on current density, water flow rate and water conductivity have been investigated. Ozone production is favoured by high flow rate and low conductivity of the electrolysed water.
The electrogeneration of hydroxyl radicals was studied at a synthetic B-doped diamond (BDD) thin film electrode. Spin trapping was used for detection of hydroxyl radicals with 5,5-dimethyl-1-pyrroline-N-oxide and with salicylic acid using ESR and liq. chromatog. measurements, resp. The prodn. of H2O2 and competitive oxidn. of formic and oxalic acids were also studied using bulk electrolysis. Oxidn. of salicylic acid gives hydroxylated products (2,3- and 2,5-dihydroxybenzoic acids). The oxidn. process on BDD electrodes involves hydroxyl radicals as electrogenerated intermediates. [on SciFinder (R)]
Electrolysis in aq. 1M HClO4 and 1M H2SO4 solns. was carried out under galvanostatic conditions using B-doped diamond electrodes (BDD). Analyses of the oxidn. products showed that in 1M HClO4 the main reaction is oxygen evolution, while in H2SO4 the main reaction is the formation of H2S2O8. In both electrolytes small amts. of O3 and H2O2 are formed. Finally, a simplified mechanism involving hydroxyl radicals formed by H2O discharge is proposed for H2O oxidn. on B-doped diamond anodes. [on SciFinder (R)]