Green hydrogen production mediated by hydrogel thin films prepared from poly(N-isopropylacrylamide) and graphitic carbon nitride photocatalyst with platinum cocatalyst is investigated. The swelling behavior under humid conditions for various catalyst loadings is discussed, and internal morphology is probed by neutron scattering techniques. Correlation between microstructure and hydrogen evolution indicates that a hydrophilic polymer–substrate interface enhances the hydrogen generation.

Photocatalytic water splitting enables the generation of green hydrogen (H₂). In this framework, water and sunlight are the sustainable sources. Photocatalyst-loaded hydrogel materials have already shown their potential as a water storage and catalyst host matrix for H₂ production. This study explores the thin film geometry of such systems to demonstrate the scalability of photocatalysis. Graphitic carbon nitride is used as a catalyst and combined with platinum as a co-catalyst. The resulting catalytic centers are introduced in poly(N-isopropylacrylamide) hydrogel thin films. First, the swelling behavior of the resulting hybrid hydrogels is studied under high relative humidity, and the influence of different catalyst loadings is discussed. Then, time-of-flight neutron reflectometry is used to access the vertical material composition inside the hybrid thin film in the dry state, which shows an enrichment layer of catalyst at the substrate–bulk interface. Operando grazing incidence small-angle neutron scattering displays the microscopic changes happening under heavy water (D₂O) vapor and light irradiation. Next, gas chromatography demonstrates the potential of the studied hydrogel films by determining their H₂ production rates. The recorded H₂ production is correlated to the microstructure analysis and reveals the importance of the observed catalyst enrichment layer.