Compressive strain in Cu catalysts: Enhancing generation of C₂₊ products in electrochemical CO₂ reduction

Elastic strain in Cu catalysts enhances their selectivity for the electrochemical CO₂ reduction reaction (eCO₂RR), particularly toward the formation of multicarbon (C₂₊) products. However, the reasons for this selectivity and the effect of catalyst precursors have not yet been clarified. Hence, we employed a redox strategy to induce strain on the surface of Cu nanocrystals. Oxidative transformation was employed to convert Cu nanocrystals to Cu_xO nanocrystals; these were subsequently electrochemically reduced to form Cu catalysts, while maintaining their compressive strain. Using a flow cell configuration, a current density of 1 A/cm² and Faradaic efficiency exceeding 80% were realized for the C₂₊ products. The selectivity ratio of C₂₊/C1 was also remarkable at 9.9, surpassing that observed for the Cu catalyst under tensile strain by approximately 7.6 times. In-situ Raman and infrared spectroscopy revealed a decrease in the coverage of K⁺ ion-hydrated water (K·H₂O) on the compressively strained Cu catalysts, consistent with molecular dynamics simulations and density functional theory calculations. Finite element method simulations confirmed that reducing the coverage of coordinated K·H₂O water increased the probability of intermediate reactants interacting with the surface, thereby promoting efficient C-C coupling and enhancing the yield of C₂₊ products. These findings provide valuable insights into targeted design strategies for Cu catalysts used in the eCO₂RR.