A photosensitizer–polyoxometalate dyad that enables the decoupling of light and dark reactions for delayed on-demand solar hydrogen production

Decoupling the production of solar hydrogen from the diurnal cycle is a key challenge in solar energy conversion, the success of which could lead to sustainable energy schemes capable of delivering H2 independent of the time of day. Here, we report a fully integrated photochemical molecular dyad composed of a ruthenium-complex photosensitizer covalently linked to a Dawson polyoxometalate that acts as an electron-storage site and hydrogen-evolving catalyst. Visible-light irradiation of the system in solution leads to charge separation and electron storage on the polyoxometalate, effectively resulting in a liquid fuel. In contrast to related, earlier dyads, this system enables the harvesting, storage and delayed release of solar energy. On-demand hydrogen release is possible by adding a proton donor to the dyad solution. The system is a minimal molecular model for artificial photosynthesis and enables the spatial and temporal separation of light absorption, fuel storage and hydrogen release.