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

Compressive strain on copper surfaces significantly reduces water surface coverage compared to surfaces under tensile strain. This leads to a higher preference for C2+ products, negatively impacting the production of C1 products. Quantitatively, copper surfaces with compressive strain have a ratio of 9.9 for C2+ products to C1 products, while surfaces under tensile strain have a ratio of only 1.3. Additionally, copper surfaces under compressive strain demonstrate an impressive C2+ product selectivity of 80.15% at a current density of 1 A/cm2. [Display omitted] 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 CuxO 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.