Noble-metal-based high-entropy-alloy nanoparticles for electrocatalysis

Since the two seminal papers were published independently in 2004, high-entropy-alloys (HEAs) have been applied to structural and functional materials due to the enhanced mechanical properties, thermal stability, and electrical conductivity. In recent years, HEA nanoparticles (HEA-NPs) were paid much attention to in the field of catalysis for the promoted catalytic activity. Furthermore, the various ratios among the metal components and tunable bulk and surface structures enable HEAs have big room to enhance the catalytic performance. Especially, noble-metal-based HEAs displayed significantly improved performance in electrocatalysis, where the ‘core effects’ were employed to explain the superior catalytic activity. However, it is insufficient to understand the essential mechanism or further guide the design of electrocatalysts. Structure–property relationship should be disclosed for the catalysis on HEA-NPs to accelerate the process of seeking high effective and efficient electrocatalysts. Therefore, we summarized the recent advances of noble-metal-based HEA-NPs applied to electrocatalysis, such as hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, methanol oxidation reaction, ethanol oxidation reaction, formic acid oxidation reaction, hydrogen oxidation reaction, carbon dioxide reduction reaction and nitrogen reduction reaction. For each electrocatalytic reaction, the reaction mechanism and catalyst structure were presented, and then the structure–property relationship was elaborated. The review begins with the development, concept, four ‘core effect’ and synthesis methods of HEAs. Next, the electrocatalytic reactions on noble-metal-based HEA-NPs are summarized and discussed independently. Lastly, the main views and difficulties pertaining to structure–property relationship for HEAs are discussed.