Enhanced CH4 yields by interfacial heating-induced hot water steam during photocatalytic CO2 reduction

[Display omitted] •Polypyrrole as a photothermal membrane (PM) generates hot water steam for CO2 reduction.•A preferential H2O adsorption mechanism during CO2 reduction over TiO2 is proposed.•The well-designed route achieves efficient CO2 reduction and high CH4 selectivity.•The enhanced mechanism was discussed to present the superiority of designed route. The adsorption and activation of H2O vapor on photocatalyst is highly important for CO2 reduction yet having been overlooked among the large amounts of reports. Herein, we demonstrate a preferential H2O adsorption mechanism to replace the previously assumed competitive adsorption, that is, H2O molecules were pre-adsorbed on the catalytic sites and dissociated to provide protons for the activation of the adsorbed CO2 molecules. Thanks to a photothermal membrane (PM)-induced interfacial heating, the generation of hot steam dramatically increases the partial pressure of water vapor from 17 to 43 kPa at ambient pressure, which favors H2O adsorption on TiO2 surface. The well-designed TiO2+PM system achieves selective reduction of CO2 to CH4 with a high evolution rate of 18.3 μmol g−1 h−1, about 3.3 times of that in the absence of PM. The light-to-heat conversion makes the utilization of light energy more efficient, not merely for the photogeneration of charge carriers.