Optimizing Cu+-Cu0 synergy by operando tracking of Cu2O nanocatalysts during the electrochemical CO2 reduction reaction

Tracking the evolution of electrocatalysts over oxide-derived Cu materials during the electrochemical CO 2 reduction reaction (eCO 2 RR) is pivotal for optimizing the product selectivity toward desired multi-carbon (C 2+ ) products. However, the identification of the true intermediate active catalyst is still unclear. Here, we adopted a multi-modal characterization approach, primarily based on operando powder X-ray diffraction and operando micro-Raman spectroscopy, to study three Cu 2 O precursors with different morphologies, namely, octahedral (O-), cubic (C-), and nanowire (N-Cu 2 O). This multi-modal approach allows us to investigate the Cu 2 O nano-crystallites from the interface to the bulk structure. The results suggested notably different electrochemical reduction kinetics. 26.1% O-Cu 2 O and 90.6% C-Cu 2 O were reduced to much smaller Cu(0) domains after two hours of time-on-stream; N-Cu 2 O, with notably higher surface-to-volume ratio, was completely reduced within 45 min of time-on-stream. We accordingly observed a structure-reactivity correlation where a more intricate Cu 2 O/Cu grain network (and hence Cu + -Cu 0 junctions) as observed in O-Cu 2 O, can lead to stable and quantitative production of ethylene at the Faradic efficiency of around 40% (in stark contrast to those of C- and N-Cu 2 O). The synergy between the Cu 2 O and Cu phases was also verified by density functional theory calculations. The upshifted d -band center of Cu 2 O/Cu in O-Cu 2 O is the most conducive toward the production of ethylene, whereas the downshifted d -band center of Cu 2 O/Cu in C-Cu 2 O leads to a decreased production of ethylene in the expense of unwanted production of hydrogen. We envisage that system optimization and design of new catalysts will become more facile and efficient using a related multi-modal operando characterization philosophy.