Collaborative rapid reduction promoted synthesis of highly alloyed AuAg aerogels for selective CO2 reduction to CO

Abstract

Developing electrocatalysts combining both high selectivity and durability toward CO₂ electrochemical reduction reaction (CO₂RR) to high value products is of great importance but challenging. The favorable influences of high alloying degree on electrocatalytic performance have been frequently revealed in various electrochemical energy conversions whereas rarely studied in CO₂RR. Herein, we propose a facile “one-pot galvanic replacement reaction-chemical reduction collaborative rapid reduction strategy” (GRR-CR) for the synthesis of highly alloyed Au₅₀Ag₅₀ aerogel (Au₅₀Ag₅₀-① AG) that exhibits high CO selectivity and high stability in CO₂RR. During the synthesis, galvanic replacement reaction (GRR) between HAuCl₄ and Ag and the reduction of metal ions by NaBH₄ proceed simultaneously. The large number of vacancies generated during GRR facilitate the mutual diffusion and alloying of Au and Ag atoms, leading to high alloying degree in Au₅₀Ag₅₀-① AG. Compared with the Au₅₀Ag₅₀ aerogel obtained by two-step gelation method (Au₅₀Ag₅₀-② AG) with certain micro-phase separation, the Au₅₀Ag₅₀-① AG showed much better CO₂RR performance. Specifically, at −0.7 V vs. RHE, the FE_CO of Au₅₀Ag₅₀-① AG achieve 97.8 %, much higher than 61.7 % for the Au₅₀Ag₅₀-② AG. Besides, the intrinsic activity J_{CO ECSA} of Au₅₀Ag₅₀-① AG is 4.3 times that of the Au₅₀Ag₅₀-② AG, and the Au₅₀Ag₅₀-① AG shows good durability with the FE_CO remains 87.3 % after 18 h. Theoretical simulation proved that the increase of alloying degree is conducive to reducing the energy barrier of CO₂-CO rate-determining step, promoting the formation of *COOH and *CO, and improves the overall performance of CO₂RR. This work sheds promising light on the design of CO₂RR electrocatalyst of both high selectivity and stability especially toward CO product.