Figure 2 - uploaded by Gustav Karl Henrik Wiberg
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2-4: Simulation of the systematic potential error resulting from an uncompensated solution resistance. A faradaic current is plotted as a function of potential without (black line), with 10 Ω (blue line) and 30 Ω (green line) solution resistance.
Source publication
Das Ziel dieser Arbeit kann in drei verschiedene Bereiche unterteilt werden: die Entwicklung eines state-of-the-art elektrochemischen Versuchsaufbaus und zwei separater nachfolgender experimenteller Studien im alkalischen Elektrolyt. Diese Studien zeigen die Leistungsfähigkeit des experimentellen Aufbaus und fokussieren auf unterschiedlichen Modell...
Citations
... Furthermore, the scan rate effect on ORR, where faster scans exhibit larger activities, has to be considered, 44 especially as iR post-correction leads to currentdependent scan rates. 45 Another scanning technique is cyclic amperometry. Thereby, a certain current range (not potential) is scanned. ...
... The electrolyte was either 1.0 M HClO4 or 1.0 M KOH aqueous solution. The effective solution resistance was determined online with the help of a superposed AC signal (5mV, 5kHz) and was compensated to a value below 5 Ω via an analogue positive feedback scheme of the potentiostat [28]. ...
The electrocatalytic oxidation of small organic compounds such as methanol or formic acid has been the subject of numerous investigations in the last decades. The motivation for these studies is often their use as fuel in so-called direct methanol or direct formic acid fuel cells, promising alternatives to hydrogen-fueled proton exchange membrane fuel cells. The fundamental research spans from screening studies to identify the best performing catalyst materials to detailed mechanistic investigations of the reaction pathway. These investigations are commonly performed in standard three electrode electrochemical cells with a liquid supporting electrolyte to which the methanol or formic acid is added. In fuel cell devices, however, no liquid electrolyte will be present, instead membrane electrolytes are used. The question therefore arises, to which extend results from conventional electrochemical cells can be extrapolated to conditions found in fuel cells. We previously developed a gas diffusion electrode setup to mimic “real-life” reaction conditions and study electrocatalysts for oxygen gas reduction or water splitting. It is here demonstrated that the setup is also suitable to investigate the properties of catalysts for the electro-oxidation of small organic molecules. Using the gas diffusion electrode setup, it is seen that employing a catalyst - membrane electrolyte interface as compared to conventional electrochemical cells can lead to significantly different catalyst performances. Therefore, it is recommended to implement gas diffusion electrode setups for the investigation of the electro-oxidation of small organic molecules.
... The electrolyte was either 1.0 M HClO4 or 1.0 M KOH aqueous solution. The effective solution resistance was determined online with the help of a superposed AC signal (5mV, 5kHz) and was compensated to a value below 5 Ω via an analogue positive feedback scheme of the potentiostat [28]. ...
The electrocatalytic oxidation of small organic compounds such as methanol or formic acid has been the subject of numerous investigations in the last decades. The motivation for these studies is often their use as fuel in so-called direct methanol or direct formic acid fuel cells, promising alternatives to hydrogen-fueled proton exchange membrane fuel cells. The fundamental research spans from screening studies to identify the best performing catalyst materials to detailed mechanistic investigations of the reaction pathway. These investigations are commonly performed in standard three electrode electrochemical cells with a liquid supporting electrolyte to which the methanol or formic acid is added. In fuel cell devices, however, no liquid electrolyte will be present, instead membrane electrolytes are used. The question therefore arises, to which extend results from conventional electrochemical cells can be extrapolated to conditions found in fuel cells. We previously developed a gas diffusion electrode setup to mimic “real-life” reaction conditions and study electrocatalysts for oxygen gas reduction or water splitting. It is here demonstrated that the setup is also suitable to investigate the properties of catalysts for the electro-oxidation of small organic molecules. Using the gas diffusion electrode setup, it is seen that employing a catalyst - membrane electrolyte interface as compared to conventional electrochemical cells can lead to significantly different catalyst performances. Therefore, it is recommended to implement gas diffusion electrode setups for the investigation of the electro-oxidation of small organic molecules.
... In all cases, a background subtraction was performed to remove any contributions from capacitive and surface oxidation processes according to [13]. The iR-drop was measured and compensated according to the methodology used in [13,14]. In brief, the solution resistance was recorded online with the potentiostat (ECi-200 Nordic Electrochemistry Aps c/o Skelvangsvej 43, DK-8920 Randers NV, Denmark) by superimposing a 5 kHz, 5 mV AC signal, and compensated for by an analogue positive feedback scheme. ...
There have been several reports concerning the performance improving properties of additives, such as polyvinylidene difluoride (PVDF), to the membrane or electrocatalyst layer of proton exchange membrane fuel cells (PEMFC). However, it is not clear if the observed performance enhancement is due to kinetic, mass transport, or anion blocking effects of the PVDF. In a previous investigation using a thin-film rotating disk electrode (RDE) approach (of decreased complexity as compared to membrane electrode assembly (MEA) tests), a performance increase for the oxygen reduction reaction (ORR) could be confirmed. However, even in RDE measurements, reactant mass transport in the catalyst layer cannot be neglected. Therefore, in the present study, the influence of PVDF is re-examined by coating polycrystalline bulk Pt electrodes by PVDF and measuring ORR activity. The results on polycrystalline bulk Pt indicate that the effects of PVDF on the reaction kinetics and anion adsorption are limited, and that the observed performance increase on high surface area Pt/C most likely is due to an erroneous estimation of the electrochemical active surface area (ECSA) from CO stripping and Hupd.
... The roughness factor (ratio between real and geometric surface area) of the Pt electrode is around 1.7-1.9. The solution resistance was online recorded with the potentiostat (ECi-200 Nordic Electrochemistry) by superimposing a 5 kHz, 5 mV AC signal and compensated for by an analogue positive feedback scheme [39]. The effective solution resistance was around 2V. ...
... The difference in hysteresis between the polarization curves recorded in the different acids, however, is less known. It is very intriguing that in the mixed kinetic/diffusion controlled potential region of the ORR in 0.75 M H 3 PO 4 almost no hysteresis is seen, as if the process is in steady state; a hysteresis indicates non-equilibrium conditionsmostly of the coverage with oxygenated species during the potential scan [39,44,48]. ...
In the presented work, we investigate the oxygen reduction reaction (ORR) in half-cell measurements employing different electrolytes. The aim is to compare the ORR inhibition due to anion adsorption at transient as well as steady state conditions. It is found that the ORR inhibition at the platinum − phosphoric acid electrolyte interface is a relative slow, time dependent process. The major inhibition is not observed in transient polarization curves but only under steady state conditions. This observation is in contrast to the typical ORR inhibition due to anion adsorption as observed for example in sulfuric acid electrolyte. In sulfuric acid the inhibition is fast and then stays more or less constant in time. As a consequence of our findings, common transient measurements of the ORR activity might not be sufficient to investigate suitable mitigation strategies for the ORR inhibition in phosphoric acid electrolyte. Such strategies need to take steady state conditions into account.
In order to explain the slow ORR inhibition in phosphoric acid electrolyte, two possible explanations are discussed. Either the adsorption of phosphate is a slow, complex process, where a fast adsorption step is followed by a consecutive filling of the surface, or a mass transfer barrier develops at the polarized phosphoric acid − electrode interface. The latter might be the viscoelectric effect that is known from colloidal science.
... special module (MultiWE32) is needed to utilise multiple working electrodes. This can also be achieved with homemade circuit design module consisting of several trans-resistance amplifiers in parallel, one for each WE [10]. This enables simultaneous biasing of 8 working electrodes with just one reference and one counter electrode. ...
... This enables simultaneous biasing of 8 working electrodes with just one reference and one counter electrode. Further, specific details about this principle can be found in PhD thesis of Dr. Gustav Karl Henrik Wiberg [10]. We want to note that one could also use an electrochemical multiplexer or just a potentiostat and measure each WE separately. ...
The most common approach in the search for the optimal low temperature fuel cell catalyst remains “trial and error”. Therefore, large numbers of different potential catalytic materials need to be screened. The well-established and most commonly used method for testing catalytic electrochemical activity under well-defined hydrodynamics is still thin film rotating disc electrode (TF-RDE). Typically this method is very time consuming and is subjected to impurity problems. In order to avoid these issues a new multielectrode electrochemical cell design is presented, where 8 different electrocatalysts can be measured simultaneously at identical conditions.
The major advantages over TF-RDE method are:
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Faster catalyst screening times.
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Greater impurity tolerance.
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The option of internal standard.
... The counter electrode was a Pt mesh. The solution resistance between the working electrode and the reference electrode was measured by an AC signal [12], and compensated electronically by using a positive feedback scheme. All experiments were performed at room temperature. ...
We employ a recently developed stripping protocol to examine the equilibrium coverage of oxygenated species and their influence on the oxygen reduction reaction (ORR) and the hydrogen oxidation reaction (HOR). In particular we aim to distinguish between dynamic and steady state conditions and establish if distinctive potential regions exist where the different respective oxygenated species OHad, Oad and Pt-oxide dominate.
... The electrochemical experiments were conducted in the previously described GDE cell setup using an in-house developed potentiostat and software. 12 The electrolyte was concentrated H 3 PO 4 (Merck Suprapur ® ) and used as received. As working electrode served the HSA catalyst modified GDL of which 0.786 cm 2 was exposed to the electrolyte. ...
We present a detailed description of the construction and testing of an electrochemical cell setup allowing the investigation of a gas diffusion electrode containing carbon supported high surface area catalysts. The setup is designed for measurements in concentrated phosphoric acid at elevated temperature, i.e., very close to the actual conditions in high temperature proton exchange membrane fuel cells (HT-PEMFCs). The cell consists of a stainless steel flow field and a PEEK plastic cell body comprising the electrochemical cell, which exhibits a three electrode configuration. The cell body and flow field are braced using a KF-25 vacuum flange clamp, which allows an easy assembly of the setup. As demonstrated, the setup can be used to investigate temperature dependent electrochemical processes on high surface area type electrocatalysts, but it also enables quick screening tests of HT-PEMFC catalysts under realistic conditions.
Replacing critical raw materials employed in water electrolysis applications as electrocatalysts with earth-abundant materials is paramount for the future upscaling to industrial dimensions. In that regard, Ni and Ni-based multimetallic hydroxides, above all NiFe-hydroxides, have shown promising performance towards the oxygen evolution reaction (OER) in alkaline conditions. However, it has been shown that the extraordinary performance of these materials is owed largely to Fe impurities found in commercial KOH from which electrolyte solutions are prepared. The mechanism of action of these impurities is still not fully understood, and therefore, at the heart of ongoing discussions. In this study, we investigate the OER activity of different nanostrcutured (Ni1-xFex)OOH samples and find their activities to be influenced differently by the presence of Fe impurities in the electrolyte. From the gathered data, we conclude that the presence of Fe impurities impacts gravely the structure sensitivity of the OER. In purified electrolyte solutions the OER appears to be a structure-sensitive reaction while this seems not to be the case in the presence of said impurities.
We present a study concerning the influence of the diffusion of H+ and OH− ions on the hydrogen and oxygen evolution reactions (HER and OER) in aqueous electrolyte solutions. Using a rotating disk electrode (RDE), it is shown that at certain conditions the observed reaction rates do not depend on the kinetics but on diffusion properties; In fact we demonstrate how studying these reactions in 0.1 M non-buffered aqueous electrolytes with pH-values ranging between pH 1 to pH 13, the diffusion coefficients of H+ and OH− ions can be determined. Within the experimental error limits, we found no pH dependency on the diffusion coefficients for any of the investigated ions.
