Photocatalytic Water Splitting – Towards Robust Water Oxidation Catalysts József S. Pap HAS Centre for Energy Research 3 rd European Energy Conference Budapest, October

I. The Energy Carrier Problem

 H r ° = -890 kJ/mol  H r ° = -286 kJ/mol How to make it renewable? PHOTOCATALYTIC WATER SPLITTING (18×10 9 tons of water, carried by Danube in 3 months) Energy from Covalent Bonds Sunlight: 10 5 x our consumption Problem: intermittant and diffuse

II. Energy Storage in Plants

Energy Storage in Covalent Bonds: Photosynthesis energy gradient slow fast (P + Q A - ) charge separation: 25 Å, in a few ps (P + Q A - ) charge separation: 25 Å, in a few ps O2O2 NADP-H (H-H) I. McConnell, G. Li, G. W. Brudvig, Chem. Biol. 2010, 17, 434

S n = Mn 4 Ca cluster ( s -1 ) Water oxidation by the Oxygen Evolving Complex (OEC)

III. Artificial systems – General Considerations

Why Molecular Catalysts? „Whether water splitting is achieved by electrolysis using electricity generated by photovoltaic devices or dye- sensitized solar cells, or by artificial photosynthesis remains at this point unclear.... The durability, scalability, cost and efficiency will in the long run decide which approach to water splitting and hydrogen generation will win this competition.” P. Du, R. Eisenberg, Energy Environ. Sci. 2012, 5, 6012

e-acceptor: 1.Chemical oxidant: CAN, S 2 O 8 2-, IO 4 -, SO Electrode: GCE, ITO, TiO 2, FTO 3.Photosensitizer + electrode, or chemical oxidant, [Ru(bpy) 3 ] 2+ e-acceptor: 1.Chemical oxidant: CAN, S 2 O 8 2-, IO 4 -, SO Electrode: GCE, ITO, TiO 2, FTO 3.Photosensitizer + electrode, or chemical oxidant, [Ru(bpy) 3 ] 2+ Buffer, or base Investigation of Water Oxidation Catalysts (WOCs)

IV. General considerations, advances...and plans

ScTiVCrMnFeCoNiCuZnYZrNbMoTcRuRhPdAgCd LaHfTaWReOsIrPtAuHg oxo-wall How to form an O=O bond? (1) M=O (2) Which transition metal?

Catalysts – strategies Ru - heterocyclic ligands - bridging ligands - carbon-free ligands - axial co-ligands

Non-symmetric Bidentate Ligands – an Outlook J. S. Pap, J. Kaizer, W. R. Browne, et al., Chem. Commun., submitted

Cu Catalysts – strategies - cheap - modular design - easy to characterise - minimal light absorption in the visible region

Cu Catalysts – strategies L. Szywriel, J. S. Pap, et al., unpublished results

1.Stability (10 6 <TON) 2.Sensitivity (anions, impurities) 3.High overpotential of electrocatalytic water oxidation (>0.2 V Ru, >0.5 V Cu) 4.Rate (small TOFs, typical for heterogeneous systems) 1.Stability (10 6 <TON) 2.Sensitivity (anions, impurities) 3.High overpotential of electrocatalytic water oxidation (>0.2 V Ru, >0.5 V Cu) 4.Rate (small TOFs, typical for heterogeneous systems) Further Obstacles

Thank you for attention! Köszönöm a figyelmet! Acknowledgements János Bolyai Research Scholarship (HAS) University of Pannonia József Kaizer Gábor Speier University of Groningen Wesley R. Browne Apparao Draksharapu University of Wroclaw Lukasz Szywriel Aix-Marseille Université Michel Giorgi

J. Gascon, M. D. Hernández-Alonso, A. R. Almeida, G. P. M. Van Klink, F. Kapteijn, G. Mul, ChemSusChem 2008, 1, 981 Metal-Organic Frameworks, Ed. L. R. MacGillivray, John Wiley & Sons, Hoboken, New Jersey, Metal-Organic Frameworks (MOF) as photocatalysts?

Co Catalysts – strategies

2. Ligandumok tervezése és komplexeik vizsgálata ML complex precursor MO x L-dependent WOC V. Artero, M. Fontecave, Chem. Soc. Rev. 2013, 42, 2338 D. Hong, J. Jung, J. Park, Y. Yamada, T. Suenobu, Y.-M. Lee, W. Nam, S. Fukuzumi, Energy Environ. Sci. 2012, 5, 7606

Homogeneous or heterogeneous? - surface analytical methods (XPS, TEM, DLS) - kinetics (induction period, reproducibility) - poisoning of catalyst (Hg, PPh 3, thiophene,...) - comparison with metal oxides C.-F. Leung, S.-M. Nq, C.-C. Ko, W.-L. Man, J. Wu, L. Chen, T.-C. Lau, Energy Environ. Science 2012, 5, Ligands and Complexes

Catalysts – strategies Mn

Katalizátorok – stratégiák Fe