Hydrogen Oxidation Artifact During Platinum Oxide Reduction in Cyclic Voltammetry Analysis of Low-Loaded PEMFC Electrode
- PDF / 792,072 Bytes
- 11 Pages / 595.276 x 790.866 pts Page_size
- 3 Downloads / 201 Views
ORIGINAL RESEARCH
Hydrogen Oxidation Artifact During Platinum Oxide Reduction in Cyclic Voltammetry Analysis of Low-Loaded PEMFC Electrodes S. Prass 1
&
J. St-Pierre 2 & M. Klingele 1 & K. A. Friedrich 3,4 & N. Zamel 1
Accepted: 12 October 2020 # The Author(s) 2020
Abstract An artifact appearing during the cathodic transient of cyclic voltammograms (CVs) of low-loaded platinum on carbon (Pt/C) electrodes in proton exchange membrane fuel cells (PEMFCs) was examined. The artifact appears as an oxidation peak overlapping the reduction peak associated to the reduction of platinum oxide (PtOx). By varying the nitrogen (N2) purge in the working electrode (WE), gas pressures in working and counter electrode, upper potential limits and scan rates of the CVs, the artifact magnitude and potential window could be manipulated. From the results, the artifact is assigned to crossover hydrogen (H2X) accumulating in the WE, once the electrode is passivated towards hydrogen oxidation reaction (HOR) due to PtOx coverage. During the cathodic CV transient, PtOx is reduced and HOR spontaneously occurs with the accumulated H2X, resulting in the overlap of the PtOx reduction with the oxidation peak. This feature is expected to occur predominantly in CV analysis of low-loaded electrodes made of catalyst material, whose oxide is inactive towards HOR. Further, it is only measurable while the N2 purge of the WE is switched off during the CV measurement. For higher loaded electrodes, the artifact is not observed as the electrocatalysts are not fully inactivated towards HOR due to incomplete oxide coverage, and/or the currents associated with the oxide reduction are much larger than the spontaneous HOR of accumulated H2X. However, owing to the forecasted reduction in noble metal loadings of catalyst in PEMFCs, this artifact is expected to be observed more often in the future. Keywords Cyclic voltammetry . Oxidation artifact . Platinum electrode . Low loading . Hydrogen crossover
Introduction Cyclic voltammetry (CV) analysis is a widely used technique to examine the electrochemical active surface area (ECSA) of proton exchange membrane fuel cell (PEMFC) electrodes [1]. During CVs, currents associated to adsorption limited electron-transfer reactions on the catalyst surfaces are measured as a response to potential scans. The ECSA is then * S. Prass [email protected] 1
Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstr. 2, 79114 Freiburg, Germany
2
Hawaii Natural Energy Institute, University of Hawaii, Manoa, 1680 East-West Road, POST 109, Honolulu, HI 96822, USA
3
Institute of Engineering Thermodynamics, German Aerospace Center, Pfaffenwaldring 38-40, 70569 Stuttgart, Germany
4
Institute of Building Energetics, Thermal Engineering and Energy Storage (IGTE), University of Stuttgart, Pfaffenwaldring 31, 70569 Stuttgart, Germany
determined either from the electrical charges transferred during the under-potential deposition of hydrogen (HUPD) or from the charges associated to the oxidation of adsorbed carbo
Data Loading...
