The frequency and severity of droughts worldwide is expected to increase due to anthropogenic climate change 4, 5, and a drought was even declared in the majority of areas in England by the Environment Agency in 2022 6. Additionally, the use of pure water for hydrogen production may further strain the water supply chain. Even small amounts of contaminants in the feedstock can severely reduce the lifetime and performance of photocatalytic systems 1, and feasibility analyses often underestimate the cost of purified water and its transportation, which can be as high as US$45 per tonne in some regions 2, 3. Photocatalysis can enable solar energy to be stored directly in the form of chemical fuels such as green hydrogen produced from water splitting, but its need for pure water limits its commercial viability, particularly in regions facing water scarcity.

This work provides a new concept for developing an off-grid energy production/storage solution and is a first step towards alleviating both energy and water supply challenges. This integrated system maintains operational stability in seawater and other aqueous waste streams for over 154 h due to the isolation of the PC from contaminants in the liquid feedstock.

Specifically, an ultraviolet light-absorbing RhCrO x–Al:SrTiO 3 PC is deposited on top of a floating, visible and infrared light-absorbing porous carbon SVG, which produces green fuel with a solar-to-hydrogen efficiency of 0.13 ± 0.03% and 0.95 kg m −2 h −1 of water vapour as the feed for the PC and collectable purified water. Here we report a hybrid device consisting of a photocatalyst (PC) and a solar vapour generator (SVG) for simultaneous overall water splitting and water purification from open water sources. Photocatalytic water splitting converts sunlight directly into storable hydrogen, but commonly involves the use of pure water and land for plant installation while generating unusable waste heat.

Phase 10 phase sheet