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

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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.