Designing N-Confused Metalloporphyrin-Based Covalent Organic Frameworks for Enhanced Electrocatalytic Carbon Dioxide Reduction

Electrochemical conversion of carbon dioxide (CO2) into value-added products is promising to alleviate greenhouse gas emission and energy demands. Metalloporphyrin-based covalent organic frameworks (MN4-Por-COFs) provide a platform for rational design of electrocatalyst for CO2 reduction reaction (CO2RR). Herein, through systematic quantum-chemical studies, the N-confused metallo-Por-COFs are reported as novel catalysts for CO2RR. For MN4-Por-COFs, among the ten 3d metals, M = Co/Cr stands out in catalyzing CO2RR to CO or HCOOH; hence, N-confused Por-COFs with Co/CrN3C1 and Co/CrN2C2 centers are designed. Calculations indicate CoNxCy-Por-COFs exhibit lower limiting potential (-0.76 and -0.60 V) for CO2-to-CO reduction than its parent CoN4-Por-COFs (-0.89 V) and make it feasible to yield deep-reduction degree C-1 products CH3OH and CH4. Electronic structure analysis reveals that substituting CoN4 to CoN3C1/CoN2C2 increases the electron density on Co-atom and raises the d-band center, thus stabilizing the key intermediates of the potential determining step and lowering the limiting potential. For similar reason, changing the core from CrN4 to CrN3C1/CrN2C2 lowers the limiting potential for CO2-to-HCOOH reduction. This work predicts N-confused Co/CrNxCy-Por-COFs to be high-performance CO2RR catalyst candidates. Inspiringly, as a proof-of-concept study, it provides an alternative strategy for coordination regulation and theoretical guidelines for rational design of catalysts.