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

Abstract

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.

Electron‐Rich Pincer Ligand‐Coupled Cobalt Porphyrin Polymer with Single‐Atom Sites for Efficient (Photo)Electrocatalytic CO2 Reduction at Ultralow Overpotential

“…[2][3][4][5][6][7] Among various catalytic materials for CO 2 RR, molecular electrocatalysts such as porphyrin and phthalocyanine complexes have been the most investigated ones due to their well-defined catalytic sites (M-N 4 ) and tunable structures that can offer a potential to explore the structure-activity relationship by using the*CO binding energy (E ad (*CO)) as a descriptor. [8][9][10][11][12][13] However, those molecular electrocatalysts usually have high overpotential and low current density due to the imperfect electron transfer capability and poor conductivity. [14][15][16][17][18] Thus, structural regulation has been performed by introducing functional groups (e.g., electron-donating, electron-withdrawing, and π-conjugated substituents) to the macrocyclic skeleton or varying the central metals.…”

Boosting CO2Electroreduction over a Cadmium Single‐Atom Catalyst by Tuning of the Axial Coordination Structure

“…The coordination structure around the metal atoms of SACs can alter the selectivity and activity of CO 2 RR. Currently, the active centers of the common M‐N‐C for CO 2 RR are the four‐coordinated structure of the M‐N 4 moiety, [39–42] and the M‐N 4 moiety exhibits a symmetric electronic distribution resulting from the symmetrical planar structure. Recently, the efficiency of CO 2 RR has been significantly improved over the M‐N 5 ‐C, [43–45] which resembled the axial ligand‐coordinated natural metal enzymes, indicating that the axial coordination environment plays a crucial role on the adsorption and activation of the CO 2 RR‐relevant species.…”

Solar‐powered chemistry: Engineering low‐dimensional carbon nitride‐based nanostructures for selective CO2 conversion to C1C2 products

“…The porous skeleton and carbon defects were formed with the release of NH 3 , HBr, and other gases 119 . Carbon‐vacancy defects can also serve as anchoring sites for dopants or single atom catalysts 120,121 . For example, single atom Pd catalysts, which were coordinated with pyridinic nitrogen in the pristine g‐C 3 N 4 framework, exemplified a higher formation energy (4.27 eV) compared to Pd atoms anchored on the C‐defect sites through coordination with N atoms (<2.7 eV) 122 …”