-band state control engineering over ZnIn2S4 for enhanced photoreduction of CO2 to CH4

Metal-based photocatalysts with d10 electronic configurations exhibit good photocatalytic performance due to strong band edge dispersion, however, the weak bonding between d10 metal sites and CO2 through 2p-3d orbital hybridization limits their activity and selectivity for CO2 to CH4 conversion. Herein, a strategy for modulating the d-band center is proposed to promote the formation of CH4 in the photocatalytic CO2 reduction process. In a model system taking ZnIn2S4 (ZIS) as photocatalysts, highly thermodynamically electronegative elements (such as Bi, Cu, and Co) are doped to upshift the d-band center of ZIS, enhance the selectivity and yield of CH4. In the absence of cocatalysts or photosensitizers, the CO2 photoreduction products of all doped ZIS samples shifts from pure CO to a mixture of CO and CH4, with CH4 being the predominant product. Among all samples, Bi-doped ZnIn2S4 (Bi-ZIS) demonstrates the highest performance, achieving a CH4 selectivity of 63.68 % and a high evolution rate of 21.07 µmol·g−1·h−1 during visible-light-driven CO2 reduction. Density functional theory (DFT) calculations indicate that doping highly electronegative elements can modulate the electron cloud distribution of ZIS, thereby raising its d-band center. This shift reduces the energy barrier for CO2 photoreduction to CH4, enhancing the binding energy between active sites and intermediates (such as *OCH2 and *OCH3), facilitating the formation of CH4. Consequently, this study not only validates the effectiveness of the d-band center modulation strategy but also offers a novel perspective for optimizing the activity and product selectivity of d10 metal-based photocatalysts in CO2RR.