Scaling Relations on High-Entropy Alloy Catalyst Surfaces

Scaling and Brønsted–Evans–Polanyi (BEP) relations have proven immensely powerful in catalysis theory. The relations provide an understanding of the Sabatier principle in a quantitative fashion, such that we can calculate the adsorption energy that most optimally compromises between a low reaction barrier and a not too strong adsorption. Scaling and BEP relations are usually mapped out for pure metal surfaces, and it is not directly clear how they translate to complex alloy surfaces, e.g., high-entropy alloys (HEAs). The scaling relation between *OH and *OOH is one of the most studied and best understood. Generally, both *OH and *OOH adsorb on a single surface atom, so HEAs do not change the established scaling relation but rather widen the distribution of available adsorption energies. The situation can be different for reactions at multiatom surface sites. In the reaction between O* and *CO to form CO2, the species interact with more surface atoms at the initial state compared to the transition state, so for a given reaction energy, HEAs allow for lower activation energies than pure metals. The reason is that HEA surfaces can make the transition state more similar to the initial state without the need of steps or other geometric features.