Structure-activity relationships of polyoxometalate catalysts for visible light-driven hydrogen evolution

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Poster, René Moré, 340
Publication date: 5th February 2015

Water splitting into hydrogen and oxygen is a sustainable and flexible solution to today's energy and climate problems.^(1-3) A system for photocatalytic water splitting needs to be composed of a light harvesting unit, a water oxidation catalyst (WOC) and a water reduction catalyst (WRC). ⁽²⁾ Polyoxometalates (POMs) are water-soluble metal-oxo-clusters consisting of W, Mo and V in their highest oxidation states. Because of their rich redox chemistry, they are already widely used as catalysts for photo-induced water splitting.^(1,3) They are mainly used as WOC and only a handful of examples POMs used as WRC are reported. Generally, exploration of new POM based photocatalysts is fairly empirical with no structure-activity relationships (SARs) for POM based photocatalysts at hand. The limited number of POM-WRCs have been tested for photocatalytic activity under very different conditions, frequently in the presence of a noble metal co-catalyst. ⁽⁴⁾ Furthermore, these photocatalytic reactions often require organic solvents or mixed organic/water media. ⁽⁵⁾ Herein we present a systematic study of SARs observed for visible light-driven hydrogen evolution catalyzed by Keggin-type POMs ([Ni(OH₂)XW₁₁O₃₉]^n-;X = P, Si, Ge). These systems do not require any noble metal cocatalyst and work in aqueous solution. ⁽⁶⁾ Their photocatalytic activity can be tuned by the choice of the heteroatom. The highest turnover number (TON) was found for the germanium containing representative with a value of 37.1±0.4. The photocatalytic results were correlated with electrochemical investigations and DFT calculations.
Figure 1. Influence of the heteroatom on photocatalytic performance of Keggin-type POMs.
1. Lv, H.; Geletii, Y. V.; Zhao, C.; Vickers, J. W.; Zhu, G.; Luo, Z.; Song, J.; Lian, T.; Musaev, D. G.; Hill, G. L. Polyoxometalate water oxidation catalysts and the production of solar fuel, Chem. Soc. Rev.,2012, 41, 7572-7589. 2. Balzani, V.; Credi, A.; Venturi, M. Photochemical conversion of solar energy, ChemSusChem, 2008, 1, 26-58. 3. Sumliner, J. M.; Lv, H.; Fielden, J.; Gelettii, Y. V.; Hill, C. L. Polyoxometalate multi-electron-transfer catalytic systems for water splitting. Eur. J. Inorg. Chem. 2014, 635-644. 4. Zhao, J.; Ding, Y.; Wei, J.; Du, X.; Yu, Y.; Han, R. A molecular Keggin polyoxometalate catalyst with high efficiency for visible-light driven hydrogen evolution, Int. J. Hydrogen Energ.,2014, 39, 18908-18918. 5. Lv, H.; Guo, W.; Wu, K.; Chen, Z.; Bacsa, J.; Musaev, D. G.; Geletii, Y. V.; Lauinger, S. M.; Lian, T.; Hill, C. L. A noble-metal-free tetra-nickel polyoxotungstate catalyst for efficient photocatalytic hydrogen evolution, J. Am. Chem. Soc., 2014, 136, 14015-14018. 6. von Allmen, K.; Moré, R.; Müller, R.; Soriano-López, J.; Linden, A.; Patzke, G. R., Keggin-type Ni substituted polyoxometalates as hydrogen evolution catalysts: Photochemical structure-activity relationships, submitted.

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