Platinum‐Doped Carbon Nitride‐Loaded Poly( <i>N</i> ‐Isopropylacrylamide) Hydrogel Thin Films for Green Hydrogen Production Systems: Morphological Study for Higher Efficiency

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.