Integrable utilization of intermittent sunlight and residual heat for on-demand CO₂ conversion with water

Abundant residual heat from industrial emissions may provide energy resource for CO₂ conversion, which relies on H₂ gas and cannot be accomplished at low temperatures. Here, we report an approach to store electrons and hydrogen atoms in catalysts using sunlight and water, which can be released for CO₂ reduction in dark at relatively low temperatures (150-300 °C), enabling on-demand CO₂ conversion. As a proof of concept, a model catalyst is developed by loading single Cu sites on hexagonal tungsten trioxide (Cu/WO₃). Under light illumination, hydrogen atoms are generated through photocatalytic water splitting and stored together with electrons in Cu/WO₃, forming a metastable intermediate (Cu/H_xWO₃). Subsequent activation of Cu/H_xWO₃ through low-temperature heating releases the stored electrons and hydrogen atoms, reducing CO₂ into valuable products. Furthermore, we demonstrate the practical feasibility of utilizing natural sunlight to drive the process, opening an avenue for harnessing intermittent solar energy for CO₂ utilization.