Oxygen-Substituted Porous C₂N Frameworks as Efficient Electrocatalysts for Carbon Dioxide Electroreduction

The electrochemical carbon dioxide reduction reaction (CO₂RR) provides a green avenue for decarbonizing the conventional chemical industries. Here, a structure-selectivity relationship of catalysts is pivotal for the control of a highly selective and active CO₂RR pathway. We report the fabrication of an oxygen-substituted C₂N as metal-free catalyst (O─C₂N) for electrochemical CO₂─to─CO conversion with tunable O microenvironment. Combined spectroscopic analysis reveals a fine tailored N─C─O moiety in O─C₂N, where C─O─C species (e.g., ring in-plane ether) become the dominant oxygen configurations at higher pyrolysis temperatures. Based on experimental observations, a correlation between the exocyclic O-substituted N─C─O─C moieties and CO selectivity is established, giving clear chemical tools for active structure design. The optimized O─C₂N electrocatalysts with the dominant appearance of C─O─C moieties exhibit an outstanding 2e^- CO₂RR performance with a CO selectivity up to 94.8%, which can be well maintained in a practical flow-cell reactor with an adjustable syngas feature.