Modulation Engineering of Graphitic/Pyrrolic Nitrogen Co-Doped Porous Carbon-Based Electrocatalysts with Abundant Active Sites for Efficient CO2 Reduction.

Abstract

Developing metal-free catalysts is critical to addressing the issues of susceptibility to poisoning and deficient durability in the electrocatalysis of metal-based materials for CO2 reduction reaction (CO2RR). Herein, N-doped carbon nanoparticles (NCs) with a specific ratio of graphitic/pyrrolic N, high specific surface area, and abundant nanopores are synthesized by pyrolyzing a Cu and Zn co-coordinated polymer with bis(imino)-pyridine ligands. Results demonstrate that precise co-incorporation of Cu and Zn in the precursor effectively modulates the N doping species and ratios of NCs, as well as the pore structure, resulting in significantly distinct CO2RR behaviors. The NCs synthesized by the precursor with the ratio of Zn and Cu ions (1:4), featuring graphitic-N and pyrrolic-N in the ratio of 2:1 and high specific surface area (896.8 m2 g-1), exhibit a low onset potential of -0.4 VRHE, an exceptional CO Faradaic efficiency of 96.1%, and a power density of 0.8 mW cm-2 in a Zn-CO2 battery. Theory calculations reveal that regulating the graphitic/pyrrolic N ratio can redistribute the localized atoms' charge density, which enhances the adsorption of intermediate COOH* and mobilizes multiple active atomic sites favoring CO2RR. The discovery in this work provides a new understanding for the design of advanced metal-free CO2RR electrocatalysts.