Photothermal catalytic hydrogen production coupled with water purification using a chitosan hydrogel-based membrane

The integrated photothermal catalytic technology that combines photothermal membrane distillation and water splitting for simultaneously producing freshwater and hydrogen is a promising solution to address water resource and energy crises. However, interfacial salt crystallization during seawater evaporation and achieving stable hydrogen production remain key challenges. This study develops a chitosan/agarose hydrogel-based photothermal catalytic composite membrane (HPCM) for solar-driven water-hydrogen coproduction. The membrane employs a hierarchical architecture featuring an upper hydrophilic chitosan/agarose hydrogel layer that enables rapid water transport and in-situ salt rejection through its three-dimensional porous network, effectively preventing salt crystallization at the evaporation interface. The lower layer consists of a hydrophobic PTFE membrane loaded with Pt-TiO 2 nanoparticles, which drives photocatalytic water splitting under illumination while leveraging PTFE's microporosity to enhance hydrogen evolution. The dual-layer architecture simultaneously enables integrated desalination and hydrogen production. The hydrogel layer effectively prevents salt accumulation to ensure long-term operational stability, while the Pt-TiO 2 /PTFE layer efficiently catalyzes hydrogen generation and enhances gas diffusion. HPCM composite membrane was integrated into an air-gap membrane distillation (AGMD) system. The HPCM-AGMD demonstrates exceptional desalination performance (>99.9% salt rejection) and operational stability under 1.0 sun irradiation. Under 1.5 sun, the system achieves a water production flux of 0.52 kg m −2 h −1 and a hydrogen production rate of 3.00 mmol m −2 h −1 . Cycling and continuous operation tests confirm the system's durability, while outdoor experiments further validate its practical feasibility under natural sunlight. This work offers a new approach to developing efficient, compact, and low-maintenance solar energy utilization systems.