Monolithic photocatalyst for overall water splitting based on gaseous water harvest

Nanocatalysts show high photocatalytic activity in overall water splitting (OWS) due to their abundant active sites and short charge diffusion paths. However, they are prone to agglomerate, especially in slurry reactors, leading to complex recovery processes. Moreover, powder photocatalytic water splitting systems relying on solid-liquid-gas three-phase reactions are inherently limited by challenges including continuous water supply and blockage of active sites by adhering H₂/O₂ gas bubbles. This study presents a comprehensive solution to these challenges through the development of a novel porous monolithic catalyst which can capture water via LiCl-mediated vapor adsorption, and immobilize the nanocatalysts within a three-dimensional gel network. This design promotes the rapid release of H₂/O₂ gas products via the pores without liquid water. Structural characterizations combined with density functional theory based calculations reveal that electronic interactions between the amide groups of polyacrylamide (PAM) and the powder catalyst significantly enhance the photon absorption, charge separation, and reaction kinetics for OWS. Molecular dynamics simulations demonstrate that LiCl salts function as effective water transport mediators by reducing the interaction energy and disrupting hydrogen bonding networks between PAM and H₂O molecules, thereby facilitating rapid water diffusion through the polymer matrix. These synergistic effects collectively contribute to the remarkable 4.6-fold enhancement in H₂/O₂ evolution rates observed for the porous monolithic catalyst compared to its powder counterpart.