Dynamics of Pt oxidation and reduction upon square wave excitation in fuel cells

Pt and Pt alloy catalysts are used at the cathode of proton exchange membrane fuel cells to reduce O2 into H2O. Their activities are dependent on the O adsorption energy EOads, which is governed by its d-band centre according to the DFT calculations. Alloys raise the d-band centre and therefore reduce EOads, improving the activity in oxygen reduction reaction (ORR). However, this understanding is mainly gained from steady state measurement and is lack of measurement on the surface dynamics. Here we will measure the transient catalyst response upon rapid switching of electrochemical potentials via Pt L3 and Co K edge quick XAFS measurement. This study will determine 1) the rate of Pt and Co oxidation and reduction upon different electrochemical potentials; 2) the dynamics of Pt and Co local coordination environment; 3) the dynamics of surface adsorbed O species via difference XANES. This study is of fundamental importance to determine and quantify the rate of surface reaction.