Abstract
The electrocatalytic CO2 reduction reaction (CO2RR) has been a fast developing and innovative topic in recent years. It may enable efficient reduction of carbon emission, as well as store renewable electricity into chemical bonds in fuels or other chemicals. However, due to the complexity of reaction factors and mechanisms, the activity and selectivity of CO2RR have yet to be further optimized in order to realize commercial applications. Specifically, the high selectivity of CO2 reduction products (especially for multi-electron-transfer and multi-carbon reduction products), lower overpotentials, high energy efficiencies, good stability, and low fabrication cost are required. In this Spotlight, we focus on the design of active sites in heterogeneous catalysts for electrochemical CO2 reduction, and we provide several strategies to target those challenges in this field. First, as the major side reaction in aqueous solutions, the hydrogen evolution reaction can be inhibited by increasing the energy barrier for H-2 formation and tuning the electrolyte diffusion toward the electrocatalyst surface, thus enhancing the Faradaic efficiencies of CO2RR products. Second, the proximity of adjacent catalytic sites suggests a strong capability for tuning the coupling efficiency of multiple carbon atoms. Third, the active sites of heterogeneous electrocatalysts can be generated by different defects, including single-atom doping, anion vacancy, alloy formation, and lattice defects, which can lead to distinctively different production distributions. Finally, a solar-driven electrocatalytic CO2 reduction system was developed, enabling a high solar-to-fuel photoconversion efficiency. Further investigations of heterogeneous electrocatalysts and reaction systems are expected to enhance the electrochemical CO2RR performances toward the application level.