Multi-functional photocatalytic systems for solar fuel production

Solar fuel production from water has received increasing attention due to increasing energy and environmental concerns. Herein we highlight dual- and multi-functional photocatalytic systems, which have both photosensitizing and thermal redox functions for solar fuel production. For example, polymeric cyano (CN)-bridged heteronuclear metal complexes act as dual functional photoredox catalysts that incorporate both a light harvesting photosensitizer and redox catalytic sites for the photocatalytic oxidation of water and reduction of dioxygen to produce H₂O₂. On the other hand, metal-organic frameworks (MOFs) contain both organic parts which act as photosensitizers and inorganic metal parts which act as redox catalysts, catalyzing water oxidation, H₂ evolution, CO₂ reduction and H₂O₂ production. An organic photoredox catalyst can be incorporated into nano-sized mesoporous cellular silica foams together with a redox catalyst for water oxidation, H₂ production, CO₂ reduction and H₂O₂ production. Finally, construction of multi-functional catalytic systems is discussed for solar-driven production of H₂ as molecular models of photosystem I (PSI) and photosystem II (PSII) in photosynthesis.