Low temperature and rapid photothermal oxidation of liquid gallium for circular hydrogen production

Hydrogen is a clean energy carrier with significant promises for a sustainable future, yet many established production routes operate under undesirable conditions or constraints, motivating the search for alternative production pathways. Here, our approach uses photothermal oxidation of liquid gallium to generate hydrogen from both freshwater and seawater. The exposure to light thermally heats up liquid gallium droplets to a temperature suitable for fast gallium-water interaction, producing gallium oxyhydroxide and hydrogen. The light exposure also boosts the reaction by breaking the oxide layer on the surface of liquid gallium immersed in water, allowing continuous interactions between the water molecules and the surface of liquid gallium droplets. The gallium oxyhydroxide that is produced can be electrochemically reduced, allowing metal regeneration, thereby enabling circular hydrogen production. In this work, we show that photothermal activation of liquid gallium provides a rapid and circular route for generating hydrogen from diverse water sources.