Operando Probing of Nanocracking in CuO-Derived Cu During CO₂ Electroreduction

Cu is the only metallic catalyst for the CO₂ electroreduction reaction (CO₂RR) that produces significant multicarbon (C₂₊) products. Among various Cu-based materials, the oxide-derived Cu (OD-Cu) exhibits enhanced electrocatalytic activity. Although diverse types of grain boundaries and residuary Cu⁺ from precatalyst reconstruction have been reported as the active species, the formation mechanisms and design principles for OD-Cu catalysts remain lacking. A major hurdle is the inability to directly monitor the structural evolution of OD-Cu catalysts under operating conditions due to the fast, complex dynamic transformation behavior of precatalyst activation during CO₂RR. Here we reported operando studies of OD-Cu catalysts origin and evolution from CuO nanowires during CO₂RR using a multimodal platform coupling the newly developed high-resolution electrochemical liquid cell transmission electron microscopy (EC-TEM) with time-resolved and high energy resolution fluorescence detected X-ray absorption spectroscopy (XAS). We discovered the formation pathways of catalytic active sites through nanocracking of CuO nanowire precatalyst during rapid reduction to metallic Cu. The nanocrack networks further reconstructed to a high surface-to-volume ratio structure, resulting in a high density of active sites. Electrocatalytic performance testing in reactors of different scales (TEM micro-electrolyzer, H-type cell, and MEA), coupled with complementary ex situ structural characterizations, suggested this behavior was general across all catalytically relevant conditions and was critical for enhanced C₂₊activity. These findings suggested a means to optimize OD-Cu structures for high activity and our advanced operando approach opened new opportunities for mechanistic insights to enable improved control of catalyst structure and performance from precatalyst.<br/><br/>Acknowledgement: This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (BES), Materials Sciences and Engineering Division under Contract No. DE-AC02-05-CH11231 within the in-situ TEM program (KC22ZH).