In-situ X-ray absorption and electrochemical study of electrocatalysts for polymer electrolyte membrane (PEM) fuel cells

An in-situ X-ray absorption spectroscopy cell was designed to study the structural and electronic properties of high performance polymer electrolyte fuel cell (PEFC) electrocatalysts. The cell was operated as a standard fuel cell and X-ray absorption data were collected simultaneously while varying fuel cell operating conditions. The cell was used to examine platinum-ruthenium alloy electrocatalysts incorporated into the anode of a fuel cell membrane and electrode assembly. The in-situ Pt L_III and Ru-Kedge X-ray absorption Near Edge Structure (XANES) data were collected at five selected current densities of the operating fuel cell. A fresh membrane electrode assembly (MEA) and a conditioned MEA were studied at different operating conditions of the fuel cell and different feed (pure H₂ or H₂/CO [100 ppm CO]) at the anode. The in-situ Pt L_III-edge and Ru K-edge XANES of the fuel cell MEAs showed metallic characteristics under all operating conditions. These results demonstrate that under the reducing conditions of normal fuel cell operation, the Pt-Ru catalyst exists as a metallic phase(s). This study also concludes that conditioning the fuel cell over time does not affect the gross chemistry of the catalyst structure; the improvement of performance between a fresh and conditioned fuel cell is due to the wetting and hydration. The cell design enabled the first reported in-situ fuel cell study at a synchrotron source without the use of supplemental electrolytes.