title: Porphyrin-Sensitized Evolution of Hydrogen using Dawson and Keplerate Polyoxometalate Photocatalysts.
abstract: Hydrogen evolution using photocatalytic systems based on artificial photosynthesis is a major approach toward solar energy conversion and storage. In the polyoxometalate-based photocatalytic systems proposed in the past, middle/near UV light irradiation and noble-metal catalysts were mainly used. Although recently polyoxometalates were sensitized in visible light, photosensitizers or catalysts based on noble metals, and/or poor activity of polyoxometalates were generally obtained. Here we show the highly efficient [turnover number (TON)=215] hydrogen evolution induced by the zinc(II) mesotetrakis(N-methyl-pyridinium-4-yl)porphyrin (ZnTMPyP4+) sensitization of a series of polyoxometalate catalysts (two Dawson type, P2Mo18O626-and P2W18O626-anions, and one Keplerate {Mo132} cluster) in a visible-light-driven, noble-metal-free, and fully water-soluble system. We attributed the high efficiency for hydrogen evolution to the multi-electron reduction of polyoxometalates and found that: (a) both Dawson polyoxometalates exhibit higher hydrogen evolution efficiency upon ZnTMPyP4+sensitization in relation to the direct photoreduction of those compounds; (b) the P2Mo18O626-anion is more efficient (TON=65 vs. 38, respectively) for hydrogen evolution than the P2W18O626-anion; and (c) the high nuclearity Keplerate {Mo132} cluster exhibits the highest efficiency (TON=215) for hydrogen evolution compared with the polyoxometalates studied.
authors: Laboratory of Bioinorganic Chemistry, Department of Chemistry, University of Crete, Voutes Campus, 70013, Heraklion, Crete, Greece.
authors: Athanassios
authors: A
authors: Panagiotopoulos
authors: Institute of Nanoscience and Nanotechnology (INN), National Center for Scientific Research (NCSR) "Demokritos", Patr. Gregoriou E' & 27, Neapoleos str., 153 41, Agia Paraskevi, Attica, Greece.
authors: Antonios M
authors: 0000-0001-6806-2935
authors: AM
authors: Douvas
authors: Institute of Nanoscience and Nanotechnology (INN), National Center for Scientific Research (NCSR) "Demokritos", Patr. Gregoriou E' & 27, Neapoleos str., 153 41, Agia Paraskevi, Attica, Greece.
authors: Panagiotis
authors: P
authors: Argitis
authors: Laboratory of Bioinorganic Chemistry, Department of Chemistry, University of Crete, Voutes Campus, 70013, Heraklion, Crete, Greece.
authors: Athanassios G
authors: AG
authors: Coutsolelos
mesh_terms: D002384:Catalysis; D006859:Hydrogen / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D055668:Photochemical Processes; D011166:Porphyrins / Q000737:chemistry*; D017973:Tungsten Compounds / Q000737:chemistry*; D000099294:Polyoxometalates
chemical_list: D006859:Hydrogen; D011166:Porphyrins; D017973:Tungsten Compounds; C102296:polyoxometalate I; D000099294:Polyoxometalates
keywords: hydrogen evolution; photocatalysis; photoreduction; polyoxometalates; porphyrin