Precise design of nickel phthalocyanine molecular structure: Optimizing electronic and spatial effects for remarkable electrocatalytic CO2 reduction

Abstract

The atomic dispersion offered by transition metal-nitrogen-carbon electrocatalysts (M-N-C) represents a promising system for efficient catalysis of the CO2 reduction reaction (CO2RR) to a CO product. However, accurate elucidation of the catalytic mechanism of M-N-C catalysts synthesized by pyrolysis is impeded by the ambiguity of the coordination environment of the MNx active site. Herein, by combining theoretical and experimental methods, the influence of the electronic and geometric effects of the NiN4 site in a group of nickel phthalocyanine (NiPc)-based molecular catalysts on the performance of CO2RR are investigated. Density functional theory calculations indicate that only electron-withdrawing and ortho-nitro-substituted NiPc-based molecularly dispersed electrocatalysts can significantly enhance the NiN4 active site for CO2 activation. The lowest activation energy is required for forming the *COOH intermediate compared to other reference catalysts. Our modeling is in complete accordance with our experimental results, proving that the position of the substituent groups and push-pull electron effects simultaneously play crucial roles in CO2RR catalyst performance.