Porphyrin-based imine gels for enhanced visible-light photocatalytic hydrogen production

Abstract

Porphyrin-based imine gels assembled from small molecular precursors have been developed as a novel type of catalysts in hydrogen production from water splitting. The gels offer chemical variety and hierarchically porous structures and are susceptible to modification via porphyrin metal centres. The Pd gel shows cathodic electrocatalytic activity to produce H₂ when coated on FTO electrodes. The gels are stable and active for visible-light driven hydrogen production in the presence of a sacrificial electron donor and a cocatalyst. Impregnation of the Pd metal centre greatly enhances the H₂ evolution rate. The Pd gel enables efficient photocatalytic H₂ evolution via photoinjection of electrons from the light-harvesting gel network into the Pt nanoparticles. When illuminated with visible light, the Pt-doped PdTAPP–TFPT gel produces hydrogen from aqueous sodium ascorbate solution without significant degradation during four runs (1.0744 × 10⁵ μmol g⁻¹ for 120 h totally). Interestingly the wet gels show remarkably higher H₂ production efficiency than their dried counterparts.