Quick Operando Ambient Pressure Hard X-ray Photoelectron Spectroscopy for Reaction Kinetic Measurements of Polymer Electrolyte Fuel Cells
Takahiro Nakamura, Yasumasa Takagi, Suwilai Chaveanghong, Tomoya Uruga, Mizuki Tada, Yasuhiro Iwasawa, Toshihiko Yokoyama
Abstract
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 × 104 Pa (maximum 1 × 105 Pa) with the maximum time resolution of ∼200 ms. To accumulate time-resolved spectra with sufficient signal-to-noise 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 3d5/2 and S 1s HAXPES from the Pt/C cathode catalyst of polymer electrolyte fuel cells. In the Pt 3d5/2 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.