Figure 1. (a) Schematic illustration of experimental H-type electrolytic cell for electrochemical CO2 reduction; (b) Thermodynamic equilibrium potential diagram of some value-added compounds from ECR in the aqueous electrolyte (pH = 7); (c) Proposed reaction pathway of CO2 reduction to CO production.
As displayed in Figure 1c, the formation process (3) of COOH* can be divided into two concerted proton–electron transfer (CPET) steps: (1) and (2). Previous studies have demonstrated that rate-determining steps (RDS) may be (3) or (4), depending on the COOH* binding energy and the CO* desorption energy.[41,42] Therefore, the accurate regulation of the adsorption strength of key intermediates is fairly essential to exploit the reasonable electrocatalyst for reducing CO2 to CO.[43,44] Notably, except the ECR process, hydrogen adsorption on the electrocatalyst surface needs to be considered, because that HER is the main competitor of ECR. Stronger H* binding ability is required to rise HER overpotential, which will help promote the occurrence of ECR.[45,46]