Unveiling the Active Site of Metal-Free Nitrogen-doped Carbon for Electrocatalytic Carbon Dioxide Reduction

Abstract

Nitrogen-doped (N-doped) carbon materials have been widely studied for electrocatalytic CO 2 R to CO. However, the active sites in N-doped carbon remain under debate owing to the complication in N types and the challenge in controllable synthesis. Here, via an innovative approach of template-assisted pyrolysis of phthalocyanine, we achieve a controlled preparation of N types in N-doped carbon foams. Electrochemical experiments show that the catalyst dominated by graphitic N rather than other N types drives highly selective CO 2 R to CO against the hydrogen evolution reaction, which achieves a CO Faradaic efficiency of 95% at −0.5 V versus RHE and runs stably for 80 h. Theoretical calculations indicate that carbon atoms next to graphitic N are triggered for the CO production, while carbon atoms next to pyridinic N promote the hydrogen evolution and pyrrolic N disfavors both reactions. Controllable tuning of nitrogen types in nitrogen-doped carbon foams Graphitic nitrogen triggers electrocatalytic CO 2 reduction on adjacent carbon atoms Pyridinic nitrogen favors hydrogen evolution reaction at edge carbon sites Pyrrolic nitrogen disfavors both the CO 2 reduction and hydrogen evolution reactions The nature of the active sites for electrocatalytic CO 2 reduction to CO on metal-free nitrogen-doped carbon remains under debate. Here, by precisely tuning the types of nitrogen dopants, Zhang et al. elucidate that graphitic nitrogen triggers CO 2 reduction, while pyridinic nitrogen promotes hydrogen evolution and pyrrolic nitrogen disfavors both reactions.