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

Electrochemical conversion of carbon dioxide (CO 2 ) into value-added products is promising to alleviate greenhouse gas emission and energy demands. Metalloporphyrin-based covalent organic frameworks (MN 4 -Por-COFs) provide a platform for rational design of electrocatalyst for CO 2 reduction reaction (CO 2 RR). Herein, through systematic quantum-chemical studies, the N-confused metallo-Por-COFs are reported as novel catalysts for CO 2 RR. For MN 4 -Por-COFs, among the ten 3d metals, M = Co/Cr stands out in catalyzing CO 2 RR to CO or HCOOH; hence, N-confused Por-COFs with Co/CrN 3 C 1 and Co/CrN 2 C 2 centers are designed. Calculations indicate CoN x C y -Por-COFs exhibit lower limiting potential (-0.76 and -0.60 V) for CO 2 -to-CO reduction than its parent CoN 4 -Por-COFs (-0.89 V) and make it feasible to yield deep-reduction degree C 1 products CH 3 OH and CH 4 . Electronic structure analysis reveals that substituting CoN 4 to CoN 3 C 1 /CoN 2 C 2 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 CrN 4 to CrN 3 C 1 /CrN 2 C 2 lowers the limiting potential for CO 2 -to-HCOOH reduction. This work predicts N-confused Co/CrN x C y -Por-COFs to be high-performance CO 2 RR 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.