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.
@article{arxiv.2602.20784,
title = {Epitaxial Films as Model Platform for Understanding Compositionally Complex Electrocatalysts},
author = {Satyakam Kar and Alejandro E. Perez-Mendoza and Huixin Xiu and Miran Joo and Kirill V. Yusenko and Ulrich Hagemann and Christoph Somsen and Janine Pfetzing-Micklich and Christina Scheu and Corina Andronescu and Alfred Ludwig},
journal= {arXiv preprint arXiv:2602.20784},
year = {2026}
}