Electrochemically Engineered Octahedral High-Entropy Alloy Nanocrystals for Enhanced Electrocatalysis

Abstract

High-entropy alloys (HEAs) have attracted increasing attention and shown considerable promise for diverse applications. However, the shape-controlled construction of HEAs with well-defined facets remains a significant challenge due to the large chemical and structural complexity. Herein, an electrochemical square-wave potential method was developed for shape-controlled construction of octahedral PdAuAgZnCu high-entropy alloy nanocrystals (HEA-NCs) in a choline chloride-urea (ChCl-U) based deep eutectic solvent (DES). The mechanism reveals that the formation of the octahedral HEA-NCs is critically dependent on the periodic synergy between a lower potential (EL) for reductive deposition and an upper potential (EU) for oxidative dissolution. Thanks to the high-entropy composition and multi-element synergistic effect, the as-synthesized octahedral PdAuAgZnCu HEA-NCs exhibits exceptional electrocatalytic performance for hydrazine oxidation reaction (HzOR). Compared to monometallic Pd, PdAuAg ternary alloy, PdAuAgZn and PdAuAgCu quaternary alloys, the PdAuAgZnCu HEA-NCs demonstrates superior HzOR activity in an alkaline electrolyte, achieving a high current density of 157 mA cm−2 at 1.2 V vs. RHE, with a low onset potential of 0.4 V vs. RHE at 20 mA cm−2 and a Tafel slope of 141 mV dec−1. Density functional theory (DFT) calculations reveals that the Pd−Cu bridge sites on the PdAuAgZnCu(111) HEA surface possess a low activation barrier of the initial dehydrogenation of hydrazine and exhibit high activity for HzOR with Sequential Mechanism.