Photothermal　catalytic　reduction　of　carbon　dioxide　(CO2)　to　carbon　monoxide　(CO)　is　important　in　combating　climate　change　and　achieving　sustainable　development.　In　this　work,　the　In2O3/ZnS　composites　were　synthesized　using　a　simple　hydrothermal　method.　Compared　to　pure　In2O3　(CO　yield　of　1.7　μmol/g/h)　and　ZnS　(CO　yield　of　5.1　μmol/g/h),　the　optimal　composite　30-In2O3/ZnS　leads　to　a　significant　11.6　folds　and　3.9　folds　increase　in　CO　production　rate　(19.7　μmol/g/h),　showing　a　CO　selectivity　up　to　98.5　%.　This　improvement　is　due　to　the　enhanced　adsorption　and　desorption　capacity　of　gas　molecules,　the　improved　photogenerated　charge　carriers　separation,　the　interaction　between　In2O3　and　ZnS,　the　dual　defects　(Ov　and　Sv)　on　x-In2O3/ZnS.　To　elucidate　the　intermediates　and　products,　in-situ　diffuse-reflectance　infrared　Fourier　transform　spectroscopy　(DRIFTS)　was　conducted,　which　facilitated　the　formulation　of　a　plausible　mechanism.　The　CO2　molecules　are　adsorbed　and　activated　on　the　surfaces　of　the　catalysts　to　form　CO2−　species,　which　react　with　H+　and　·OH　to　generate　two　important　intermediates　of　HCO3−　and　COOH∗.　These　intermediates　further　convert　to　CO∗　in　the　subsequent　reactions,　ultimately　desorbing　from　the　catalysts　to　yield　CO　molecules.　This　work　offers　a　straightforward　and　effective　preparation　strategy　for　developing　active　photothermalcatalysts　for　CO2　reduction　with　water　vapor.　©　2025　Elsevier　Ltd