Controlling Solar Hydrogen Production by Organizing Porphyrins

In this study, a highly efficient photocatalytic H₂ production system is developed by employing porphyrins as photocatalysts. Palladium and platinum tetracarboxyporphyrins (PdTCP and PtTCP) are adsorbed or coadsorbed onto TiO₂ nanoparticles (NPs), which act as the electron transport medium and as a scaffold that promotes the self-organization of the porphyrinoids. The self-organization of PdTCP and PtTCP, forming H- and J-aggregates, respectively, is the key element for H₂ evolution, as in the absence of TiO₂ NPs no catalytic activity is detected. Notably, J-aggregated PtTCPs are more efficient for H₂ production than H-aggregated PdTCPs. In this approach, a single porphyrin, which self-organizes onto TiO₂ NPs, acts as the light harvester and simultaneously as the catalyst, whereas TiO₂ serves as the electron transport medium. Importantly, the concurrent adsorption of PdTCP and PtTCP onto TiO₂ NPs results in the most efficient catalytic system, giving a turnover number of 22,733 and 30.2 mmol(H₂ ) g(cat)^-1 .