Understanding the dynamic evolution of atomically dispersed Cu catalyst for CO2 electrochemical conversion using integrated XANES analysis and mechanistic studies.

[Display omitted] • Understanding the dynamic evolution of catalysts under reaction condition is critical to rational design of catalysts and control of catalytic properties, yet presents great challenges to both experimental and computational techniques. • Here we report an original study that aims to advance the fundemental understanding of the dynamic change of an supported Cu catalyst and the corresponding catalytic property during electrochemical reduction of CO 2 to ethanol by a comprehensive structural and mechanistic study. • This study integrates in-situ X-ray absorption near edge structure (XANES) spectroscopy with ab initio XANES simulations to identify the structural changes of the catalyst, combined with systematic density functional theory (DFT) caclulations of reaction mechanism on various catalytic sites. • The evolution of single-atom Cu to Cu nanoparticles under electrochemical condition has been identified, and Cu partcile size effect on activity and product selectivity is demonstrated. This work also demonstrates an effective strategy on studying the dynamic evolution of catalysts. Direct electrochemical conversion of CO 2 to ethanol (CH 3 CH 2 OH) offers a promising strategy to lower CO 2 emission while storing energy from renewable electricity. Our recent study reported a carbon-supported atomically dispersed Cu catalyst that achieved the highest reported selectivity for CH 3 CH 2 OH formation (91%) at a relatively low potential (-0.6 V), however, the active site structure that is responsible for such high activity and selectivity has yet to be understood. In this paper, we demonstrate a computational investigation combining X-ray absorption near edge structure (XANES) simulations and a mechanistic study via density functional theory (DFT) to understand the catalyst structures of this Cu catalyst during electrocatalysis and the corresponding reaction mechanisms of the key products. An integrated computational and experimental XANES analysis depicted the dynamic evolution of the catalytic site during electrocatalysis. The as-prepared, atomically dispersed Cu catalyst aggregates and forms metallic clusters/nanoparticles under electrochemical condition, which then break down to smaller oxidized clusters after electrocatalysis. The formed Cu clusters/nanoparticles showed distinct catalytic activity and selectivity as a function of particle size based on the mechanistic investigation using DFT, which is consistent with experimental observations for catalyst samples with different Cu loadings. This comprehensive study which combines experimental and computational XANES investigation, mechanistic study via DFT calculations, and experimental performance of the catalysts, provides unprecedented dynamic and mechanistic insights into the supported atomically dispersed metal catalysts for CO 2 reduction. Such strategy and details gained can further guide discovery of novel catalyst materials for CO 2 electrochemical reduction. [ABSTRACT FROM AUTHOR]