Electrochemical water splitting and CO2 reduction are promising processes for converting renewable energy sources to storable, high purity, carbon-free or carbon-neutral fuels, as well as commodity chemicals. The oxygen evolution reaction (OER) is key to both of these processes but suffers from slow kinetics and requires significant additional voltage to proceed. Furthermore, development of OER catalysts that are stable and active in acidic conditions could have a direct impact on improvement of devices for polymer electrolyte membrane-based water electrolyzers for fuel production. We present investigation of a class of catalysts that has demonstrated remarkable activity and stability in acidic electrolyte. Some significantly outperform rutile IrO2 and RuO2, the only other OER catalysts to have reasonable stability and activity in acidic electrolyte. Previous work has shown that a highly active catalyst surface is formed via leaching of Sr from surface layers of crystalline SrIrO3 thin films upon exposure to acidic electrolyte and electrochemical potential cycling. These experimental results are supported by DFT calculations which reveal that the SrIrO3 perovskite is thermodynamically unstable relative to aqueous Sr2+ and propose possible Sr-deficient overlayer structures that may form with electrochemical testing. Through a combination of lattice matching and ab initio molecular dynamics, anatase IrO2 and IrO3 overlayers are suggested as highly active motifs that may be present at the restructured catalyst surface. We have developed an expanded series of iridate perovskite catalysts that take advantage of cation leaching from surface layers to access unique surface structures supporting a range of catalytic activity for the OER. Catalyst activity and stability are assessed by alternating cyclic voltammetry (CV) and chronopotentiometry. X-ray photoemission spectroscopy (XPS) of the catalyst surface and x-ray diffraction (XRD) of the catalyst bulk structure before and after electrochemical testing are used to identify motifs that may be responsible for improvements in catalytic activity.

Iridate perovskites as highly active catalysts for the oxygen evolution reaction in acidic conditions

2019 Fall National Meeting

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