The Crystal Chemistry in Two Families of Compositionally Complex Oxide Electrocatalysts

Integration of renewable feedstocks into the current energy infrastructure drives the development of electrocatalysts that can maintain high surface areas and selective electrocatalytic activities under a variety of challenging chemical and environmental conditions. Recently, several compositionally complex oxides (CCOs) have been reported with intriguing and tunable electrocatalytic properties. We present recent studies on compositionally complex Rare Earth cerate oxygen evolution reaction (OER) electrocatalysts and bifunctional OER and oxygen reduction reaction (ORR) spinel ferrite electrocatalysts. A combination of local to long-range electron, x-ray and neutron scattering probes are employed to investigate their complex configurational diversity and associated structure-property trends. Relationships are explored between the cation site preferences, chemical-short-range order, and promising electrocatalytic properties achieved in the families through compositional tuning and variation in synthesis/processing conditions. Experimentally derived models are supported by Density Functional Theory calculations employing Special Quasirandom Structure models. This work highlights the importance of studying structure-property characteristics under reaction conditions and hints at the exquisite level of detail that may be required in computational and experimental approaches to guide structure-property tuning in emerging CCO OER and ORR electrocatalysts. Current challenges and future opportunities in this arena will be discussed.