Hydrogels as Functional Media in Photocatalytic Energy Systems: Toward Self-Sustained Green H₂Generation

Green hydrogen (H₂) production from photocatalytic water splitting is not yet scalable, and most green H₂ available today is still produced by water electrolysis. One of the main limitations arises from the reaction setup, where photocatalysts must be dispersed in liquid water. Hydrogels offer an alternative platform that acts simultaneously as a water reservoir and a host matrix for photocatalyst dispersion, supplying the water (H₂O) required for water splitting while preventing catalyst aggregation. When designed appropriately, catalyst-loaded hydrogels can operate in a self-sustained manner. This Perspective discusses strategies to improve catalyst dispersion and to preserve the swelling behavior that maintains water availability. Polymer networks tailored for long-term water retention can prevent dehydration and sustain H₂O feedstock during diurnal hygrometric cycles. Approaches for dark photocatalysis are also considered to enable H₂ production during the night. Finally, advanced scattering techniques are highlighted as essential tools to probe the morphology and dynamics that govern the performance of these hydrogel systems.