Topological defects are expected to locally tune the intrinsic catalytic activity of carbon materials, thanks to its asymmetric local electronic redistribution. However, owing to the high formation energy, deliberately creating high-density homogeneous topological defects in carbon networks still remains a bottleneck.

Through selectively removing pyrrolic-N and pyridinic-N dopants from N-enriched porous carbon particles via elevating temperatures in ammonia atmosphere, researchers at NIMTE successfully created high-density topological carbon defects.

The resultant topological defects were 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.

The as-prepared porous carbon materials showed an enhanced electrocatalytic CO₂ reduction performance, yielding a current density of 2.84 mA cm^-2 with a Faradaic efficiency (FE) of 95.2 % at -0.6 V versus reversible hydrogen electrode (RHE) in 0.1 M CO₂-saturated KHCO₃ electrolyte, which is among the best performances reported for metal-free CO₂ reduction electrocatalysts. 

Density Functional Theory (DFT) calculations confirmed the key role of 5-member ring C defects in CO₂ reduction.

The study has not only presented deep insights for the defect engineering of carbon-based materials, but also enhanced the understanding of electrocatalytic CO₂ reduction on carbon defects.