Figure 4 - available via license: Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
Content may be subject to copyright.
(a) LSV under illuminated conditions for the planar BiVO 4 photoanodes. (b) Comparison of LSV under illuminated conditions. (c) Current vs time at 1.23 V and (d) IPCE for 000 vs 000P and 210 vs 210P in 0.5 M Na 2 SO 4 , where significant increase in the photocurrent observed for porous samples.
Source publication
In this paper, the synergistic effect of porosity and gradient of Mo doping in BiVO4 photoanodes for improving charge separation and solar water oxidation performance is reported. A simple solution-based, three-step fabrication route was adopted using a layer-by-layer assembling technique. A water oxidation photocurrent of ∼1.73 mA cm–2 at 1.23 V v...
Contexts in source publication
Context 1
... At a higher polymer content, the thickness of the film was increased (>600 nm, Figure S3), which restricted the ability of photogenerated electrons to diffuse to reaching the back contact. The increase in porosity with increasing sacrificial polymer content was revealed in the field emission scanning electron microscopy (FESEM) images ( Figure S4a−e). It was also evident from UV−vis absorption spectra and FESEM images that the light absorption as well as porosity increased with increased layering (Figures S2b and S5a−h), and the improved performance for P100 was attributed to the optimization of light absorption and diffusion length. ...
Context 2
... fabricated planar photoanodes were then labeled as 000, 012, 222, and 210 and are schematically shown in Figure S9. According to the presumed charge separation, as a result of homojunction formation, enhanced charged separation was clearly observed for the 210 samples from the LSVs of the planar BiVO 4 photoanodes (Figure 4a) with the photocurrent of ∼0.89 mA cm −2 at 1.23 V vs RHE. This value was similar to the one reported for graded W:BiVO 4 (∼1 mA cm −2 ) at 1.23 V vs RHE. ...
Context 3
... lack of formation of porosity in this case was also revealed from the surface morphology, as shown in Figure S10b. A comparative photocurrent performance of porous and planar photoanodes (LSV under illumination of 000 vs 000P and 210 vs 210P, Figure 4b) confirmed that the incorporation of porosity improved the water oxidation performance significantly. Thus, the dominant role of porosity is supported by the stability plot and incident photon-to-current conversion efficiency (IPCE) graph as shown in Figure 4c,d. ...
Context 4
... comparative photocurrent performance of porous and planar photoanodes (LSV under illumination of 000 vs 000P and 210 vs 210P, Figure 4b) confirmed that the incorporation of porosity improved the water oxidation performance significantly. Thus, the dominant role of porosity is supported by the stability plot and incident photon-to-current conversion efficiency (IPCE) graph as shown in Figure 4c,d. From the present results, it was evident that in the case of porous gradient Mo:BiVO 4 samples, there was a synergy between the porosity and gradient doping, where the introduction of porosity enhanced light absorption, whereas gradient doping improved charge separation. ...
Similar publications
Methods of selective synthesis of C−H acetoxylated and halogenated 2‐arylbenzoxazinones were developed. The reactions went smoothly under the benign conditions and gave the corresponding products with high selectivity. The methods are compatible to the arylbenzoxazinones with either electron‐withdrawing or electron‐donating groups. Additionally, th...
Citations
... As can be seen in figure , respectively. It should be emphasized that N D values deduced from MS plots do not correspond to the absolute concentration as the model is proposed for the planar system [54]. However, this analysis could signify a qualitative trend in donor density and flat band potential values of the studied semiconductors. ...
Photoanodes with a large electrochemically active surface area, rapid charge transfer, and broadband light harvesting capacity are required to maximize the photoelectrochemical (PEC) water splitting performance. To address these features, we demonstrate that 3D hierarchal ZnO nanodendrites (NDs) can be sensitized with BiVO4 nanoislands by chemical and thermal treatments of electrodeposited Bi metal films. The flat band measurements and optical characterization suggested that the resulting heterojunction had type-II band alignment with a viable charge transfer from BiVO4 to ZnO NDs. In parallel, PL analysis revealed inhibition of the charge recombination rate by the electron transfer between BiVO4 and ZnO NDs. Upon AM 1.5 G illumination, BiVO4/ZnO NDs heterojunction yielded the highest photocurrent efficiency (0.15 mA·cm⁻² at 1.2 V vs. NHE), which was attributed to its enhanced surface area (due to the presence of small dendrite branches), extended broadband light absorption extending from UV to visible light regions, and the most efficient interfacial charge transfer as proven by electrochemical impedance spectroscopy (EIS) studies. Besides, the incident photon-to-current conversion efficiency and applied bias photon-to-current efficiency tests confirmed an improved spectral photoresponse of the heterojunction based photoanode, particularly towards the visible light spectrum. The results outline a promising synthesis route for building heterojunctions between visible light active and wide band gap semiconductors for the use as a highly efficient photoanodes in a PEC cell.
... The increased void space can eliminate the restrictions at the semiconductor and electrolyte interface and offer a large number of catalytic sites, which can effectively improve the photoelectrochemical performance. 25 The total surface area of the NRs involving both polar and non-polar sidewalls was also adequately increased for the small diameter and long NRs. Besides this, polar surfaces account for a very small fraction of the total surface area. ...
The impact of geometric features, light absorption spectra, and electrochemical active surface area on photoelectrochemical properties was investigated in this work. Nanoforests of ZnO nanorods with rationally controlled morphologies were grown on ITO substrates by the hydrothermal method and utilized as a model for this purpose. The size of the nanorods was systematically adjusted by varying the concentration of polyethyleneimine as a cation surfactant in the growth solution. It was found that the emergent geometric characteristics (i.e. the aspect ratio) increased almost at the same pace as the electrochemically active surface area, but the light scattering effect slightly increased as a result of the random spatial orientation of the nanorods. The large surface area and the void space between nanorods increased the photon-to-current conversion efficiency by promoting the hole transfer process at the electrode/electrolyte interface. A maximum photocurrent density of 0.06 mA cm-2 (0.5 V vs. NHE) for smaller diameter and length ZnO nanorods (ZnO-P1) was obtained under 365 nm UV light illumination. Additionally, we provide visual evidence that a shorter photogenerated hole diffusion distance results in improved charge separation efficiency using Mn2+ as the photogenerated hole imaging agent. Therefore, the present work demonstrates a facile strategy for nanoforest morphology improvement for generating strong contact at the ZnO NR electrode/electrolyte interface, which is favourable in energy conversion and storage technologies.
... It was also observed that the electrochemical impedance of the ZnO/CdTe heterostructure was decreased by increasing the temperature. It was due to the increase in porosity of the ZnO/CdTe by increasing the temperature as FESEM images depicted [26,40]. The increase in porosity will lead the charge transfer to become easy and fast from the semiconductor to the electrolyte. ...
... [11] On the other hand, a gradient in the charge carrier density has been experimentally achieved by only one approach: intrinsic or extrinsic compositional grading. [12][13][14][15][16][17][18][19][20][21] In light of the foregoing, in this work we propose and prove an innovative approach to improve the charge carrier selectivity in PV devices by generating for the first time grading in the shallow doping concentration, taking advantage of the O/D transition in kesterite absorbers. In particular, by controlling the local concentration of ionized Cu Zn -, V Cu -(acceptors, negatively charged), and Zn Cu + (donor, positively charged) defects. ...
Kesterite materials are among the most promising emerging photovoltaic absorbers, despite the number of challenging issues this technology presents. The use of soft thermal post-deposition treatments (PDT) is key to improving the CdS/kesterite interface quality. Thermal treatments can result in a low-temperature phase transition which affects the optoelectronic properties. In this work, the effects of applied voltage during a full device thermal PDT above the critical temperature of the phase transition are explored. The applied voltage modifies the formation energy and drives in-depth migration of ionized defects, which can generate a shallow doping density gradient (SDDG). Supporting the experimental findings, the effects of an SDDG on the current-voltage curves and the external quantum efficiency are modelled using drift-diffusion calculations. The presence of bulk recombination centers in the modelling is a key aspect to precisely reproduce the experimental results. The SDDG in opposite directions precisely matches the experimental results for opposite voltage polarizations. The effects on the band structure of the device are presented proving this as a promising strategy for improving charge carrier selectivity. In this sense, the results and their thorough physical interpretation will potentially open new perspectives in the field of materials engineering.
... To the best of our knowledge, most of the research works on gradient-doped semiconductors have so far been focused on harvesting and converting solar energy to clean and storable chemical [10,17,19,26] or electrical energy [14,16], while their application in environmental purificationwhereas both electrons and holes would participate in the photocatalytic degradation-has not been reported. Herein, we used PLD technique for the fabrication of N-doped TiO2 with the anatase phase at different doping levels of substitutional nitrogen into the TiO2 lattice. ...
... used for the precise measurement of the critical angle since the accuracy of density measurements by using XRR method highly depends on the critical angle accuracy. It is reported that increasing the porosity can enhance the specific surface area and the number of active catalytic sites and also, increase the light absorption by the formation of scattering centers inside the porous structures [26]. Highly porous photocatalysts suffer from the lack of robustness and possess high trap states and interfacial recombination centers, whereas one-dimensional columnar-like TiO2 structure reduces charge recombination rate, resulting in enhanced charge-collection efficiency [43]. ...
... The effects of morphology on the photoelectrochemical performance of semiconductors were reported in several studies [26,44,45]. Noh et al. [43] concluded that vertically-aligned onedimensional structure has a profound effect on the electron dynamics of dye-sensitized solar cells. ...
In this work, by using pulsed laser deposition (PLD) method, we incorporated nitrogen into the anatase TiO2 lattice to fabricate substitutional nitrogen doped TiO2 with different N content and film densities. All synthesized films were characterized in depth by X-ray diffraction (XRD), X-ray reflectivity (XRR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV–vis spectroscopy. In the next step, to fully leverage the band bending induced by nitrogen doping, we synthesized a six layer multiple-homojunction using gradient nitrogen doped TiO2 (g-N-TiO2) to extend the width of band bending over the bulk of the porous photocatalyst and induce an oriented electrical field perpendicular to the substrate. Following its higher photoelectrochemical (PEC) performance, the multiple-homojunction g-N-TiO2 prepared at 20 Pa with columnar-like nanostructure was used for the photocatalytic degradation of sulfamethoxazole (SMX) antibiotic in water under the simulated solar light irradiation. The results showed that compared to pristine TiO2 and non-gradient doped TiO2 (N-TiO2), the photocatalytic degradation performance of g-N-TiO2 dramatically improved in terms of SMX removal percentage, kinetics of degradation (10 times higher than TiO2) and detoxification of solution. We believe that the superior potential of the PLD technique in controlling the film density and gradient doping renders it a highly promising technique towards fabricating unique multiple-homojunctions based on gradient doped semiconductors. Besides water treatment, such formed, precisely controlled, multiple-homojunctions with low interfacial defects will provide novel insights into other applications such as solar fuels, sensors, water splitting, solar cells, etc.
... However, the semiconductor suffers from several drawbacks such as high electron-hole recombination rate, poor water oxidation kinetics and low conductivity [18,19]. Considerable effort to suppress the electronhole recombination rate and to improve the conductivity has been achieved through doping with W and Mo [20][21][22], while charge separation proved to be more effective by co-layering BiVO 4 with other semiconductors to achieve band alignments that can promote hole and electron accumulations (heterojunction), thus minimizing the recombination rate [23,24]. ...
... 61 However, the porous nature may also promote increased light absorption. 62 On the other hand, we do observe a significant electrocatalytic current also for the OER, which reaches up to 9.32 mA/cm 2 at 2 V vs RHE. The favorable conduction and photocurrents tend to be influenced by the band gap falling in the optimal range of 1.6−2.4 ...
The structural diversity of Co(II) metal centers is known to influence their physico-chemical properties. A novel 2D Co(II)-MOF {[Co5(HL)4(dpp)2(H2O)2(µ-OH)2]∙21H2O}n has been designed and synthesized by adopting mixed ligand strategy, using 1,3-di(4-pyridyl)propane (dpp) co-linker with a flexible spacer H3L (H3L: 5-(2 Carboxybenzyloxy)isophthalic acid). Co(II)-MOF features a 2D-network which is further interpenetrated among the equivalent sets and therefore results in a 3D supramolecular network. Topologically, the entire network can be viewed as a (3,4,8)-connected three nodal net with the extended point symbol of {4.5.7}4{412.52.710.94}{52.8.92.10}2, duly assigned to the novel topological type smm2. The functional utility of Co(II)-MOF is demonstrated by employing it towards Oxygen Evolution Reaction (OER) in a photoelectrochemical cell, exhibiting appreciable photocurrents of up to 5.89 mA/cm² when used as an anode in a photoelectrochemical cell, while also displaying encouraging electrocatalytic currents of 9.32 mA/cm2 (at 2.01 V vs. RHE) for the OER. Moreover, detailed Electrochemical Impedance Spectroscopy (EIS) studies confirm enhanced charge transfer kinetics and improved conductivity under illumination with minimal effect of interfacial phenomena. This work provides a reference for the expanding field of research into applications of MOF materials, and establishes MOF materials as favorable candidates for sustainable and efficient design of electrodes for water splitting.
... As early as 2011, Park and his coworkers reported the incorporation of W and Mo into the lattice of BiVO 4 films, leading to a significant enhancement in both the carrier diffusion length and photocurrent density [13]. Recently, Antony et al. [14] demonstrated a significant enhancement (up to four times) in the water oxidization photocurrent by Mo doping, and attributed it to increased charge separation and enhanced hole diffusion length (from 43 to 183 nm). Soon later, the above research group also developed a facile solution-based, three-step fabrication route to synthesize the gradient porous Mo:BiVO 4 photoanodes, leading to a water oxidation photocurrent of ~ 1.73 mA/cm 2 at 1.23 V versus (vs.) reversible hydrogen electrode (RHE) in neutral pH without using any sacrificial agent or electrocatalyst [15]. ...
The Mo-doped BiVO4 (m-BiVO4) thin films were deposited onto transparent conducting substrates via a facile metallic organic deposition method. The effect of nominal Mo doping contents on the photoelectrochemical (PEC) performance was investigated. By terms of the electrochemical impedance spectra and Mott–Schottky results, the best PEC performance appeared in the 5 and 10 at% Mo-doped BiVO4 samples was attributed to a lowering of charge transfer resistance occurred at the electrode/electrolyte interface. Moreover, a self-powered Mo:BiVO4 PEC biosensor was fabricated for detecting the glutathione (GSH), which demonstrated a rapid response, a wide detection range 5–1000 µmol/L (µM), a ultralow detect limit of 59 nM, and a sensitivity of 835 A/cm2/mM−1.
Low-cost, stable and non-toxic Bi2Fe4O9 (BFO) photoanode was used for the first time to promote glycerol aqueous solution photoelectrochemical conversion to hydrogen and value-added chemicals. The photoelectrochemical measurements were performed...
