Controlling the Macrostructure of Chromophore Hydrogels for Enhanced Photocatlytic Hydrogen Evolution

Solar fuel generation is a promising method of producing stable storage molecules like hydrogen gas using abundant sunlight as an energy source. Self-assembling chromophore amphiphiles based on perylene monoimide (PMI) can form weak hydrogels capable of producing of H₂ in water under visible light illumination. However, the high diffusivity of these gels comes at the cost of poor mechanical stability. We report here on the use the natural biopolymer sodium alginate to both promote self-assembly and immobilization PMI in a robust hydrogel. The PMI-alginate matrix can entrap catalysts in close proximity to PMI photosensitizer to enhance H₂ evolution and enable long-term reusability for up to six days. By changing the diameter and the alginate loading of the PMI-alginate gel, we showed that hydrogen production could be enhanced by reducing the mass transfer distance of reagents through the gel. <br/>The long-aspect ratio of the pi-pi stacked PMI assemblies also enables the formation of a percolation network for electrical conduction within the hydrogel network. In the hydrated state, the chromophore hydrogels displayed photoconductivity under visible light, enabling the application of these 3D hydrogels to electrodes. We then 3D printed this material on an FTO-NiO substrate to create 3D hydrogel photocathodes.