Atomic Pyridinic Nitrogen as Highly Active Metal‐Free Coordination Sites at the Biotic‐Abiotic Interface for Bio‐Electrochemical CO2 Reduction

Abstract

AbstractBio‐electrochemical conversion of anthropogenic CO2 into value‐added products using cost‐effective metal‐free catalysts represents a promising strategy for sustainable fuel production. Herein, N‐doped carbon nanosheets synthesized via pyrolysis of the zeolitic‐imidazolate framework (ZIF) are developed for constructing efficient biohybrids to facilitate CO2‐to‐CH4 conversion. The microbial enrichment and bio‐interfacial charge transfer are significantly affected by the proportion of the co‐existed graphitic‐N, pyridinic‐N, and pyrrolic‐N in the defective carbon nanosheets. It is unfolded that pyridinic‐N and pyrrolic‐N with the doped N atoms near the edge can significantly enhance the adsorption of their adjacent C atoms toward O, leading to improved microbe enrichment. Especially, pyridinic‐N which can provide one p electron to the aromatic π system, greatly enhances the electron‐donating capability of the carbon nanosheets to the microorganisms. Correspondingly, due to its largest amount of pyridinic‐N doping, the N‐doped carbon nanosheets derived from ZIF pyrolysis at 900 °C (denoted 900‐NC) achieve the highest methane production of ≈215.7 mmol m−2 day−1 with a high selectivity (Faradaic efficiency = ≈94.2%) at −0.9 V versus Ag/AgCl. This work demonstrates the effectiveness of N‐doped carbon catalysts for bio‐electrochemical CO2 fixation and contributes to the understanding of N functionalities toward microbiome response and biotic‐abiotic charge transfer in various bio‐electrochemical systems.