Epitaxial Films as Model Platform for Understanding Compositionally Complex Electrocatalysts

TL;DR

This paper introduces epitaxial films as a crystallographically-defined model system to study compositionally complex electrocatalysts, enabling detailed structure-activity analysis and advancing rational catalyst design.

Contribution

It presents a method to create epitaxial, multi-element films with controlled composition and surface quality, facilitating correlative multi-scale characterization of electrocatalysts.

Findings

Successful fabrication of smooth, epitaxial Ir-Pd-Pt-Rh-Ru films on sapphire.

Demonstration of nanoscale structure-activity mapping using combined microscopy techniques.

Establishment of a versatile platform for fundamental studies of complex electrocatalyst surfaces.

Abstract

Compositionally complex solid solutions provide a unique route for engineering high-performance electrocatalysts, where the polyelemental surface composition can be seamlessly tuned to optimize activity, selectivity, and stability. However, the mechanistic understanding of these electrocatalysts remains limited by the lack of a model system with a crystallographically-defined surface that is compatible with correlative, multi-scale characterization. Here, we present epitaxial films as a model platform for studying compositionally complex electrocatalysts. Using magnetron sputtering, we realize (111) epitaxial Ir-Pd-Pt-Rh-Ru films on (0001) sapphire substrate via a (111) Pt buffer layer, confirmed by X-ray diffraction and transmission electron microscopy. The growth approach is applicable across a broad composition range and produces smooth surfaces (root mean square roughness < 1 nm) with micrometer-sized grains in the nanoscale films. With these films, we demonstrate direct structure-activity mapping at the nanoscale through precise co-localization using micro-indents and performing correlative atomic force microscopy, electron backscatter diffraction, and scanning electrochemical cell microscopy. Our work establishes a model platform for fundamental scalebridging characterization and paves the way for rational design of compositionally complex electrocatalysts.