Metal-free Nanoporous Carbon as a Catalyst for Electrochemical Reduction of CO₂ to CO and CH₄

S-doped and dual S,N-doped polymer-derived carbons were studied as electrocatalysts for the reduction of CO₂. Higher Faradaic efficiencies for conversion to CO and CH₄ were obtained for S,N-doped carbon than its S-doped counterpart. The former showed a maximum Faradaic efficiency of 11.3 % for CO and 0.18 % for CH₄ formation. The S,N-nanoporous carbon was better at decreasing the overpotential of the reduction process. The pyridinic nitrogen groups were found to be actively participating in binding CO₂. The quaternary nitrogen and thiophenic groups were also involved in the reduction process. It is proposed that the positively charged sites on the carbon atoms, adjacent to pyridinic nitrogen, stabilize the CO₂ ^.- and COOH∗ intermediates, promoting the formation of CO. The surface basicity of the catalysts improved the CO₂ reduction selectivity when competing with H₂ evolution. N₂ adsorption measurements suggested that ultra-micropores enhance the reduction of CO₂ to CH₄. Double doped! S,N-doped polymer-derived carbons are studied as electrocatalysts for the reduction of CO₂ to CO and CH₄. Higher Faradaic efficiencies are obtained on dual S,N-doped carbon than on its S-doped counterpart. The presence of positively charged sites and the incorporation of functional groups promotes the electrochemical reduction of CO₂ and the ultra-micropores enhance the reduction of CO₂ to CH₄.