Abstract
Electroreduction of carbon dioxide into value-added fine chemicals is a promising technique to realize the carbon cycle. Recently, metal-free heteroatom doped carbons are proposed as promising cost-effective electrocatalysts for CO(2) reduction reaction (CO(2)RR). However, the lack of understanding of the active site prevents the realization of a high-performance electrocatalyst for the CO(2)RR. Herein, we synthesized metal-free N, P co-doped carbons (NPCs) for producing syngas, which is composed of H(2) and CO, by CO(2) electrolysis using inexpensive bio-based raw materials via simple pyrolysis. The syngas ratio (H(2)/CO) can be controlled within the high demand range (0.3-4) at low potentials using NPCs by tuning the N and P contents. In comparison with only N doping or P doping, N and P co-doping has a positive impact on improving CO(2)RR activity. Experimental analysis and density functional theory (DFT) calculations revealed that negatively charged C atoms adjacent to N and P atoms are the most favorable active sites for CO(2)-to-CO conversion compared to pyridinic N on N, P co-doped carbon. Introducing N atoms generates the preferable CO(2) adsorption site, and P atoms contribute to decreasing the Gibbs free energy barrier for key *COOH intermediates adsorbed on the negatively charged C atoms.