Single Ni atoms with higher positive charges induced by hydroxyls for electrocatalytic CO2 reduction

To promote Faradaic efficiency of electrocatalytic CO2 reduction reaction (CO2RR) with low-cost catalysts, single Ni-atoms with higher positive charges induced by hydroxyl was proposed to form atomically dispersed Ni-N4 structure in cheap honeycomb-like carbon matrix for electrocatalytic CO2 reduction. Extended X-ray absorption fine structure spectroscopy, aberration-corrected HAADF-STEM and X-ray photoelectron spectroscopy measurements confirmed that the active-center structure consists of single Ni atoms and the adjacent hydroxyl via hydrothermal treatment (H-Ni/NC). Density functional theory calculations indicated the isolated Ni atoms with higher positive charges induced by hydroxyl decreased the free energy of rate-limiting step to 1.05 eV for CO2RR. The Faradaic efficiency (FE) of CO2 reduction into CO was ≥ 88.0% over H-Ni/NC catalyst in the potential range of -0.5 to -0.9 V (vs. RHE). The peak CO FE reached 97% at -0.7 V due to the synergistic effect between unsaturated Ni-N4 active sites and hydroxyl species.