Regulating the Electronic Configuration of Ni Sites by Breaking Symmetry of Ni-Porphyrin to Facilitate CO₂ Photocatalytic Reduction

Adapting the coordination environment to influence the electronic configuration of active sites represents an efficient approach for improving the photocatalytic performance of the CO2 reduction reaction (CO2RR) but how to execute it precisely remains challenging. Herein, heteroatom-substitution in Ni-porphyrin to break the coordination symmetry of Ni center is proposed to be an effective solution. Based on this, two symmetry-breaking Ni-porphyrins, namely Ni(Cl)ON(3)Por and Ni(Cl)SN(3)Por, are designed and successfully prepared. By theoretical calculation, it is found that symmetry-breaking efficiently regulates the 3d orbital energy levels of Ni center. Furthermore, experimental and theoretical findings jointly revealed that coordination symmetry-breaking of Ni-porphyrins facilitates the generation of highly reactive Ni-I species during the catalytic process, effectively stabilizing and reducing the energy barrier of formation of the key *COOH intermediate. As a result, Ni(Cl)ON(3)Por and Ni(Cl)SN(3)Por gave CO production rates of 24.7 and 38.8 mmol g(-1) h(-1) as well as selectivity toward CO of 94.0% and 96.4%, respectively, outperforming that of symmetric NiN(4)Por (CO production rate of 6.6 mmol g(-1) h(-1) and selectivity of 82.8%). These findings offer microscopic insights into how to modulate the catalytic activity by precisely tuning the coordination environment of active sites and rational design of competent catalyst for CO2RR photocatalysis.