Fig. 4: Surface charge analysis and mechanistic understanding.

a Partial surface charge as a function of applied potentials from the pulse voltammetry of N–Cu SAC. b Partial current densities of CO₂RR products and atomic surface charge as a function of applied potentials for N–Cu SAC. c Partial surface charge as a function of applied potentials from the pulse voltammetry of N–Cu SAC, Fe SAC, and Co SAC. LN- represents low N-coordinated metal site. d Turnover frequencies (TOF) of CO (dash line) and partial current of CO (solid line) as a function of atomic surface charge for N–Cu SAC, Fe SAC and Co SAC. e In situ Fe K-edge EXAFS spectra of 4N-Fe(II) SAC and g in situ Co K-edge EXAFS spectra of 4N-Co(II) SAC at various applied potentials during CO₂ reduction. Potential-dependent CO₂RR product profile and corresponding coordination number extracted from EXAFS fitting on the f 4N-Fe(II) SAC and h 4N-Co(II) SAC at various potentials. Error bars represent the standard deviation of three independent measurements.