Surface-Decorated High-Entropy Alloy Catalysts with Significantly Boosted Activity and Stability

High-entropy alloy (HEA) nanoparticles are emerging catalytic materials and are particularly attractive for multi-step reactions due to their diverse active sites and multielement tunability. However, their design and optimization often involve lengthy efforts due to the vast multielement space and unidentified active sites. Herein, surface decoration of HEA nanoparticles to drastically improve the overall activity, stability, and reduce cost is reported. A two-step process is employed to first synthesize non-noble HEA (FeCoNiSn) nanoparticles and then are surface alloyed with Pd (main active site), denoted as NHEA@NHEA-Pd. As a demonstration in the ethanol oxidation reaction, a high mass activity of 7.34 A mg(Pd)(-1) and superior stability (>91.8% retention after 2000 cycles) in NHEA@NHEA-Pd are achieved, substantially outperforming traditional HEA, binary M@M-Pd (M = Sn, Fe, Co, Ni), and commercial Pd/C. In situ spectroscopy reveals that NHEA@NHEA-Pd can catalytically produce and oxidize CO at <0.5 V, which is >200 mV lower than Sn@Sn-Pd, suggesting enhanced activity in NHEA@NHEA-Pd owing to Pd's unique high-entropy coordination environment. This work provides a novel design of HEA catalysts by combining surface decoration (exposing more active sites) and high-entropy coordination (enhancing intrinsic activity and structural stability) to boost catalysts' activity and durability.