Quick Operando Ambient Pressure Hard X-ray Photoelectron Spectroscopy for Reaction Kinetic Measurements of Polymer Electrolyte Fuel Cells

We have designed and constructed a quick operando ambient pressure hard X-ray photoelectron spectroscopy (HAXPES) measurement system for the investigations of reaction kinetics in electrochemical cells under working conditions. The HAXPES measurements can be performed at typical pressures of 1 X 10(4) Pa (maximum 1 x 10(5) Pa) with the maximum time resolution of similar to 200 ms. To accumulate time-resolved spectra with sufficient signal-tonoise ratios, repeated cycles of the chemical reactions are conducted based on the repeated-cycle time-tagged method, requiring the identity of each event and the time trigger. As demonstrative experiments, we have successfully observed time-resolved operando Pt 3d(5/2). and S 1s HAXPES from the Pt/C cathode catalyst of polymer electrolyte fuel cells. In the Pt 3d(5/2) HAXPES, we have evaluated the reaction kinetics of the Pt oxidation/reduction processes at the cathode upon abrupt change of the cathode-anode bias voltage between 0.4 and 1.2 V. In the S 1s HAXPES for measurements of S species poisoning fuel cells, we have studied the contaminated anionic S adsorption and desorption kinetics on the Pt nanoparticles at the cathode. The results are comparatively discussed with previous findings.