Catalytic Duality of Platinum Surface Oxides in the Oxygen Reduction and Hydrogen Oxidation Reactions

High performing platinum—copper catalyst for self—breathing polymer electrolyte membrane fuel cell

Platinum (Pt) is the most common catalyst in Polymer Electrolyte Membrane Fuel Cells due to its ability to effectively promote the oxidation of hydrogen and reduction of oxygen. However, as a noble metal, the use of Pt should be minimized. Alloying Pt with low-cost transition metals is an effective strategy to improve catalytic activity and reduce Pt use. In this context, we report on a one-step synthesis of a Platinum/Copper (PtCu) catalyst, which can be used at both the anode and the cathode of a fuel cell. Catalysts with various Cu to Pt ratios were synthesised and in particular the PtCu catalyst at a Cu to Pt ratio of 0.5 demonstrated a high activity for hydrogen oxidation and oxygen reduction, i.e. 2.4 times superior to Pt alone. This enhanced catalytic activity was confirmed in a self-breathing PEMFC with a power output of 45.16 mW cm−2, which corresponds to a 1.4-fold increase compared to Pt alone. This is a significant improvement because 40% more power was obtained with 22% less Pt.

Graphical Abstract

Hydrogen Oxidation Artifact During Platinum Oxide Reduction in Cyclic Voltammetry Analysis of Low-Loaded PEMFC Electrodes

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.