Operando studies reveal active Cu nanograins for CO2 electroreduction

Carbon dioxide electroreduction facilitates the sustainable synthesis of fuels and chemicals(1). Although Cu enables CO2-to-multicarbon product (C2+) conversion, the nature of the active sites under operating conditions remains elusive(2). Importantly, identifying active sites of high-performance Cu nanocatalysts necessitates nanoscale, time-resolved operando techniques(3-5). Here, we present a comprehensive investigation of the structural dynamics during the life cycle of Cu nanocatalysts. A 7 nm Cu nanoparticle ensemble evolves into metallic Cu nanograins during electrolysis before complete oxidation to single-crystal Cu2O nanocubes following post-electrolysis air exposure. Operando analytical and four-dimensional electrochemical liquid-cell scanning transmission electron microscopy shows the presence of metallic Cu nanograins under CO2 reduction conditions. Correlated high-energy-resolution time-resolved X-ray spectroscopy suggests that metallic Cu, rich in nanograin boundaries, supports undercoordinated active sites for C-C coupling. Quantitative structure-activity correlation shows that a higher fraction of metallic Cu nanograins leads to higher C2+ selectivity. A 7 nm Cu nanoparticle ensemble, with a unity fraction of active Cu nanograins, exhibits sixfold higher C2+ selectivity than the 18 nm counterpart with one-third of active Cu nanograins. The correlation of multimodal operando techniques serves as a powerful platform to advance our fundamental understanding of the complex structural evolution of nanocatalysts under electrochemical conditions.

Automated summary

This study presents a comprehensive investigation of the structural dynamics of Cu nanocatalysts during the electrochemical synthesis of fuels and chemicals. The presence of active Cu nanograins under CO2 reduction conditions and their role in supporting C-C coupling reactions were observed. Quantitative structure-activity correlation revealed that a higher fraction of Cu nanograins leads to higher selectivity for C2+ products. This research provides a powerful platform for advancing our understanding of the complex structural evolution of nanocatalysts under electrochemical conditions.