American Chemical Society
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Boosting Defective Carbon by Anchoring Well-Defined Atomically Dispersed Ni–N4 Sites for Electrocatalytic CO2 Reduction

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journal contribution
posted on 2020-07-07, 10:44 authored by Xiao Yang, Jun Cheng, Xiaoxu Xuan, Niu Liu, Jianzhong Liu
To enhance the faradic efficiency of the electrocatalytic CO2 reduction reaction (CO2RR) with stable catalysts, atomically dispersed Ni–N5 active sites composed of planar Ni–N4 (in nickel phthalocyanine) coordinated with the N atom in the carbon matrix (denoted as NiPc/NC) were proposed to reduce CO2 into CO products. Extended X-ray absorption fine structure (EXAFS) spectroscopy and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) measurements confirmed that the Ni–N5 structure composed of single Ni atoms in NiPc and N doped in the carbon matrix. Density functional theory (DFT) calculations reveal that an energy barrier of only +0.89 eV is required for the process to take place on the surface of NiPc@pyridinic N. This barrier is significantly lower than in the case of NiPc@graphitic N (+2.12 eV), NiPc@pyrrolic N (+1.60 eV), and NiPc@C (+2.64 eV). This result suggests that the high CO2RR activity originates from the synergistic effect between the coordinatively unsaturated Ni–N4 sites and the surface pyridinic N species. The faradic efficiency of CO2 reduction into the CO product was ≥93% over the NiPc/NC catalyst in a wide potential range of −0.5 to −0.8 V (vs a reversible hydrogen electrode, RHE). The peak CO faradic efficiency was 98% at a potential of −0.5 V due to the synergistic effect of Ni–N4 sites in NiPc and pyridinic N atom doped in NC.