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.Graphical abstract
Highlights
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]
Depending on the electrode material analyzed, the artifact can emerge during CV analysis of low-loaded electrodes when the N2 purge is switched off during the measurement and the upper CV potential limit reaches into oxide formation potentials
We investigate an artifact peak overlapping the platinum oxide (PtOx) reduction peak measured in the cathodic transient of cyclic voltammetry analysis of ultra-low-loaded catalyst layers through a parametric analysis
Summary
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.
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