Ammonia Thermal Treatment toward Topological Defects in Porous Carbon for Enhanced Carbon Dioxide Electroreduction

Topological defects, with an asymmetric local electronic redistribution, are expected to locally tune the intrinsic catalytic activity of carbon materials. However, it is still challenging to deliberately create high-density homogeneous topological defects in carbon networks due to the high formation energy. Toward this end, an efficient NH₃ thermal-treatment strategy is presented for thoroughly removing pyrrolic-N and pyridinic-N dopants from N-enriched porous carbon particles, to create high-density topological defects. The resultant topological defects are systematically investigated by near-edge X-ray absorption fine structure measurements and local density of states analysis, and the defect formation mechanism is revealed by reactive molecular dynamics simulations. Notably, the as-prepared porous carbon materials possess an enhanced electrocatalytic CO₂ reduction performance, yielding a current density of 2.84 mA cm^-2 with Faradaic efficiency of 95.2% for CO generation. Such a result is among the best performances reported for metal-free CO₂ reduction electrocatalysts. Density functional theory calculations suggest that the edge pentagonal sites are the dominating active centers with the lowest free energy (ΔG) for CO₂ reduction. This work not only presents deep insights for the defect engineering of carbon-based materials but also improves the understanding of electrocatalytic CO₂ reduction on carbon defects.