Phase Transformation and Electrocatalytic CO₂ Reduction in Ternary Au–Ag–Cu System

Abstract This study presents a two‐step wet‐chemistry method for synthesizing AuAgCu_x nanoparticles (NPs) using AuAg NP seeds. In‐depth research investigates how composition and temperature interact to drive phase transformations, linking composition, structure, and catalytic function. These findings reveal that the alloying process exhibits unique composition‐dependent behavior under heat treatment, resulting in a transformation sequence that progresses from a ternary alloy to a binary alloy, and ultimately to an ordered structure as composition varies. In this process, silver tends to migrate away from the stable AuAg alloy, diffusing outward to the surface, while copper diffuses inward, forming an AuCu alloy. CO₂ reduction experiments demonstrate that the Faradaic efficiency of CO (FE_CO) can be finely tuned throughout the entire ternary system. Additionally, these results highlight the crucial roles of the AuCu phase and the density of grain boundaries (GB) in enhancing overall catalytic activity. This work not only sheds light on the complex interactions within ternary alloy systems but also provides valuable insights for designing more efficient electrochemical catalysts for CO₂ reduction.