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

摘要

The design of specific active sites for the carbon dioxide electro-reduction reaction (CO_2RR), is crucial for determining product selectivity and catalysis performance. Here, we present an efficient NH_3 thermal treatment for thoroughly removing the pyrrolic-N and pyridinic-N dopants from 3D N-enriched graphene analogue particles, to create high density of topological defects as active sites for CO_2RR. Firstly we found that NH_3 showed a pronounced effect of eliminating specific N-containing moieties at elevated temperatures, superior to Ar. The identification of topological defects (pentagonal carbon polygon and 585 defect) was investigated by near-edge X-ray absorption fine structure measurements and local density of states analysis, and its formation mechanism was revealed by reactive molecular dynamics simulations. The as-prepared catalysts exhibited excellent performance in flooded half-cell experiments in 0.1 M KHCO_3 reaching current densities of 2.8 mA cm~(-2) and 4.4 mA cm~(-2) with FE_(CO) of 92.7% and 89.2% at -0.6 V and -0.7 V v.s. RHE, respectively at room temperature and atmosphere pressure. These results are among the best performances reported for metal-free catalysts. Density functional theory calculations revealed that the edged pentagonal sites (penta-1 and 585-1 defects) are the dominating active centers with the lowest free energy barriers of CO_2RR for CO production.