NSF-DFG Echem: Surface Stability and Oxygen Defect Chemistry of Pyrochlore and Related High-Performing Electrocatalysts for Oxygen Evolution Reaction

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It is hypothesized that the surface Fermi energy is an important descriptor for a high activity and stability of noble-metal free electrocatalytic materials. To test this hypothesis, the project will study the Fermi energy position at the surfaces of pyrochlore electrocatalysts such as Y2Ru2O7 and RE2Ru2O7 (RE = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) for the oxygen evolution reaction in aqueous electrolytes using X-ray photoelectron spectroscopy with in situ sample processing. Interface formation with high and low work function oxides, such as RuO2 and Sn-doped In2O3 (ITO), as well as oxidizing and reducing treatments will be employed to assess the energy band alignment of the electrocatalysts in conjunction with the limits of the surface Fermi energy. The limitation of the Fermi energy is related to valence changes of the Ru ions and determines the thermodynamic stability range of the catalysts in contact with the electrolyte. A potential enhancement of stability and activity by confining the Fermi energy at the surface using suitable dopants will be assessed. The project is part of a joint NSF-DFG proposal under the lead of University of Illinois at Urbana-Champaign, where Prof. Hong Yang is responsible for sample synthesis and electrocatalytic characterization and Prof. Nicola H. Perry for defect chemistry analysis. The results obtained from the XPS analysis will be compared with defect properties and be used to develop composition and doping concepts for stable and highly active pyrochlore photocatalysts. By this, the project will advance water-splitting technology for low temperature polymer electrolyte membrane (PEM)-based electrolyzers.