Locating the cocktail and scaling-relation breaking effects of high-entropy alloy catalysts on the electrocatalytic volcano plot

Abstract

High entropy alloys (HEAs) have been the star materials in electrocatalysis research in recent years. One of their key features is the greatly increased multiplicity of active sites compared to conventional catalytic materials. This increased multiplicity stimulates a cocktail effect and a scaling-relation breaking effect, and results in improved activity. However, the multiplicity of active sites in HEAs also poses new problems for mechanistic studies. One apparent problem is the inapplicability to HEA catalysts of the currently most popular mechanistic study method, which uses the electrocatalytic theoretical framework (ETF) based on the computational hydrogen electrode (CHE). The ETF uses a single adsorption energy to represent the catalyst, i.e., a catalyst is represented by a ‘point’ in the volcanic relationship. It naturally does not involve the multiplicity of active sites of a catalyst, and hence loses brevity in expressing the cocktail effect and scaling-relation breaking effect in HEA catalysis. This paper attempts to solve this inapplicability. Based on the fact that the adsorption energy distribution of HEAs is close to a normal distribution, the mean and variance of the adsorption energy distribution are introduced as descriptors of the ETF, replacing the original single adsorption energy. A quantitative relationship between the variance and the cocktail and scaling-relation braking effects is established. We believe the method described in this work will make the ETF more effective in mechanistic studies of HEA electrocatalysis.