Abstract
Copper (Cu)-based catalysts generally exhibit high C
2+
selectivity during the electrochemical CO
2
reduction reaction (CO
2
RR). However, the origin of this selectivity and the influence of catalyst precursors on it are not fully understood. We combine
operando
X-ray diffraction and
operando
Raman spectroscopy to monitor the structural and compositional evolution of three Cu precursors during the CO
2
RR. The results indicate that despite different kinetics, all three precursors are completely reduced to Cu(0) with similar grain sizes (~11 nm), and that oxidized Cu species are not involved in the CO
2
RR. Furthermore, Cu(OH)
2
- and Cu
2
(OH)
2
CO
3
-derived Cu exhibit considerable tensile strain (0.43%~0.55%), whereas CuO-derived Cu does not. Theoretical calculations suggest that the tensile strain in Cu lattice is conducive to promoting CO
2
RR, which is consistent with experimental observations. The high CO
2
RR performance of some derived Cu catalysts is attributed to the combined effect of the small grain size and lattice strain, both originating from the in situ electroreduction of precursors. These findings establish correlations between Cu precursors, lattice strains, and catalytic behaviors, demonstrating the unique ability of
operando
characterization in studying electrochemical processes.
Copper catalysts derived from oxidized precursors typically exhibit high selectivity for CO
2
electroreduction to multicarbon products, yet the influencing factors that control the selectivity need further investigation. Here, the authors reveal that the high selectivity stems from small grain size and lattice strain due to in situ reduction of precursors.