In-Situ Spectroscopic Investigation of 3-D Gas Diffusion Electrodes for Fuel Cell Reactions in Half-Cell Setups

Abstract

Significant work has already been done in understanding proton exchange membrane fuel cells (PEMFC) over the past decades. In-situ visualization of the fuel-cell reactions has developed considerably and has also helped in understanding the challenges which still exist in various steps of electrochemical processing. Gas diffusion electrode half-cells have been widely promoted for fundamental catalysis research and when coupled with techniques like X-ray absorption spectroscopy (XAS) can be used for in-situ/operando studies of the reaction mechanisms in fuel cell reactions. This is particularly important to address the challenges in low temperature PEMFCs (eg. degradation of catalyst during durability tests) as well as high temperature PEMFCs (eg. poisoning of the Pt catalyst and low oxygen solubility in phosphoric acid).In this presentation, an effort will be made to illuminate the catalytic characteristics during oxygen reduction reaction using in-situ XAS. The co-adsorption of H3PO3 and CO on platinum catalysts will be investigated using the Δµ XANES technique by following the signatures of different species adsorbed on the catalyst surface, and the Efix technique which follows the variation of signal intensity at a fixed energy near to the white line to follow the changes in Pt oxidation. During CO removal through cyclic voltammetry in the presence of 800 µM H3PO3 (as shown in the figure provided) it is possible to see a clear change in signal intensity around the potential of 250 mVAg/AgCl, which was associated with the oxidation of H3PO3 to H3PO4, since CO oxidation takes place at higher potentials (above 600 mVAg/AgCl). It is also interesting to note that when oxidizing H3PO3 to H3PO4, the platinum surface significantly reduced. With these experiments, it can be concluded that the Efix technique has a great potential to better understand what happens to Pt during the oxidation of H3PO3, as well as to identify more clearly the oxidation potential of this species, which is not easy to do based on the electrochemical data alone. Considering that this species is one of the main species responsible for the poisoning of the Pt catalyst during the operation of fuel cells, it is extremely important to understand the life cycle of this compound so that the operating conditions can be adapted to maximize the performance of the catalyst and develop new catalysts more resistant to poisoning by phosphorous species for HT-PEMFCs.Acknowledgements:Prof. Matthias Arenz from University of Bern, Martin Prokopand Tomàs Bystrom from University of Chemistry and Technology Prague, Michael Haumann, Freie Universität Berlin are gratefully thanked for their collaboration. German Research Foundation DFG Project ID RO 2454/19-1, the Bavarian Gender Equality Grant 2019-2021 (for Women in Academia), Petra III DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, P65 beamline (I-20211432) and KMC-3 beamline BESSY (Berlin,Germany). Figure 1