In an era of shifting the energy paradigm from fossil fuels to renewable energy, CO2 reduction reaction (CO2RR) emerges as a promising approach to covert greenhouse gas into valuable chemical fuels and close the carbon cycle for a sustainable energy supply. Since Cu remains the sole element for CO2RR to multicarbon products (C2+), significant efforts have been devoted to developing Cu electrocatalysts with higher selectivity and activity. However, the complex nature of active sites and the intrinsic structures under reaction conditions have remained largely elusive due to the lack of operando/in situ methods.1-3 In our previous studies, we reported that small Cu nanoparticles (sub-10 nm NPs) showed superior C2+ superior C2+ selectivity, relative to the larger sized Cu NPs, especially at low overpotentials.4,5 In this work, we present a comprehensive operando correlative study of dynamic evolution of a family of monodisperse Cu NP ensemble electrocatalysts under CO2RR.1 Operando electrochemical liquid-cell scanning transmission electron microscopy (EC-STEM) and 4D-STEM resolves microscopic dynamic morphological and structural evolution at the nm scale. Correlated operando high-energy-resolution fluorescence-detector (HERFD) X-ray absorption spectroscopy (XAS) reveals dynamic macroscopic changes in valence states and coordination environment. Statistical analysis of interparticle dynamics was probed by operando resonant soft X-ray-based small-angle X-ray scattering (SAXS).2 The operando correlative strategies, described herein, elucidates the longstanding enigmatic nature of Cu active sites for selective CO2 electroreduction. The strategy described herein can serve as a general platform to resolve the electrocatalytic interface of nanoparticle catalysts under real-time operating conditions across multiple time and length scales, thus serving the fundamental understanding necessary to development of many other electrochemical reactions for renewable energy technologies.

Operando correlative studies of evolving Cu nanocatalysts for CO2 electroreduction

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