Role of Heteroatoms in S,N-Codoped Nanoporous Carbon Materials in CO₂ (Photo)electrochemical Reduction

Thiourea-modified wood-based activated carbon materials were evaluated as catalysts for the CO₂ electrochemical reduction reaction (CO₂ERR). The materials obtained at 950 °C showed long-term stability. The results indicated that thiophenic sulfur provides the catalytic activity for CO formation. However, it was not as active for CH₄ formation as was pyridinic N. Tafel plots suggested that the nanoporous structure enhanced the kinetics for CO₂ reduction. The electric conductivity limited the activity for CO₂ERR in the materials modified at 600, 800, and 900 °C. The effect of visible light on CO₂ERR was also investigated in this study. Upon irradiation, photocurrent was generated, and the current density increased during the CO₂ reduction process. Combined with a band-gap alignment, the results indicate that thiophenic S in the carbon matrix contributed to the sample's photoactivity in visible light. These species enhance the overall reduction process, promoting both the hydrogen evolution reaction and CO₂ reduction to CO.