Photoinduced water oxidation by a tetraruthenium polyoxometalate catalyst: ion-pairing and primary processes with Ru(bpy)3(2+) photosensitizer

Surface immobilization of a tetra-ruthenium substituted polyoxometalate water oxidation catalyst through the employment of conducting polypyrrole and the layer-by-layer (LBL) technique

A tetra Ru-substituted polyoxometalate Na10[{Ru4O4(OH)2(H2O)4}(γ-SiW10O36)2] (Ru4POM) has been successfully immobilised onto glassy carbon electrodes and indium tin oxide (ITO) coated glass slides through the employment of a conducting polypyrrole matrix and the layer-by-layer (LBL) technique. The resulting Ru4POM doped polypyrrole films showed stable redox behavior associated with the Ru centres within the Ru4POM, whereas, the POM's tungsten-oxo redox centres were not accessible. The films showed pH dependent redox behavior within the pH range 2-5 whilst exhibiting excellent stability towards redox cycling. The layer-by-layer assembly was constructed onto poly(diallyldimethylammonium chloride) (PDDA) modified carbon electrodes by alternate depositions of Ru4POM and a Ru(II) metallodendrimer. The resulting Ru4POM assemblies showed stable redox behavior for the redox processes associated with Ru4POM in the pH range 2-5. The charge transfer resistance of the LBL films was calculated through AC-Impedance. Surface characterization of both the polymer and LBL Ru4POM films was carried out using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Initial investigations into the ability of the Ru4POM LBL films to electrocatalytically oxidise water at pH 7 have also been conducted.

A Co(ii)–Ru(ii) dyad relevant to light-driven water oxidation catalysis

The covalent anchoring of a Co(ii) water oxidation catalyst to a Ru(ii) photosensitizer with potential application in artificial photosynthesis.

A functionalized, ethynyl-decorated, tetracobalt(iii) cubane molecular catalyst for photoinduced water oxidation

A new tetracobalt(iii)-oxo cubane 1 was prepared. The ethynyl groups do not affect the photocatalytic properties of 1, which, in contrast, appear to be improved.

Photoinduced hydrogen evolution by a pentapyridine cobalt complex: elucidating some mechanistic aspects

The ability of a new pentapyridine cobalt(ii) complex to power photochemical hydrogen evolution from water is investigated in detail.

Knitting the catalytic pattern of artificial photosynthesis to a hybrid graphene nanotexture

The artificial leaf project calls for new materials enabling multielectron catalysis with minimal overpotential, high turnover frequency, and long-term stability. Is graphene a better material than carbon nanotubes to enhance water oxidation catalysis for energy applications? Here we show that functionalized graphene with a tailored distribution of polycationic, quaternized, ammonium pendants provides an sp(2) carbon nanoplatform to anchor a totally inorganic tetraruthenate catalyst, mimicking the oxygen evolving center of natural PSII. The resulting hybrid material displays oxygen evolution at overpotential as low as 300 mV at neutral pH with negligible loss of performance after 4 h testing. This multilayer electroactive asset enhances the turnover frequency by 1 order of magnitude with respect to the isolated catalyst, and provides a definite up-grade of the carbon nanotube material, with a similar surface functionalization. Our innovation is based on a noninvasive, synthetic protocol for graphene functionalization that goes beyond the ill-defined oxidation-reduction methods, allowing a definite control of the surface properties.

Polyoxometalate water oxidation catalysts and the production of green fuel

In the last five years and currently, research on solar fuels has been intense and no sub-area in this field has been more active than the development of water oxidation catalysts (WOCs). In this timeframe, a new class of molecular water oxidation catalysts based on polyoxometalates have been reported that combine the advantages of homogeneous and heterogeneous catalysts. This review addresses central issues in green energy generation, the challenges in water oxidation catalyst development, and the possible uses of polyoxometalates in green energy science.