Abstract
Understanding and controlling the properties of water-splitting assemblies in dye-sensitized photoelectrosynthesis cells is a key to the exploitation of their properties. We demonstrate here that, following surface loading of a [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine) chromophore on nanoparticle electrodes, addition of the molecular catalysts, Ru(bda)(L)2 (bda = 2,2′-bipyridine-6,6′-dicarboxylate) with phosphonate or pyridyl sites for water oxidation, gives surfaces with a 5:1 chromophore to catalyst ratio. Addition of the surface-bound phosphonate derivatives with L = 4-pyridyl phosphonic acid or diethyl 3-(pyridin-4-yloxy)decyl-phosphonic acid, leads to well-defined surfaces but, following oxidation to Ru(III), they undergo facile, on-surface dimerization to give surface-bound, oxo-bridged dimers. The dimers have a diminished reactivity toward water oxidation compared to related monomers in solution. By contrast, immobilization of the Ru-bda catalyst on TiO2 with the 4,4′-dipyridyl anchoring ligand can maintain the monomeric structure of catalyst and gives relatively stable photoanodes with photocurrents that reach to 1.7 mA cm−2 with an optimized, applied bias photon-to-current efficiency of 1.5%.
Highlights
Understanding and controlling the properties of water-splitting assemblies in dye-sensitized photoelectrosynthesis cells is a key to the exploitation of their properties
A variety of anchors have been explored in dye-sensitized solar cells (DSSCs)[11], suitable candidates for dye-sensitized photoelectrosynthesis cell (DSPEC) photoanodes are dictated by the requirements for electron transfer and hydrolytic stability
In the research described here, photoanodes were prepared by co-adsorption of a phosphonatederivatized tris(2,2′-bipyridine)ruthenium(II) dichloride salt of (RuP2+) as the chromophore with pyridyl-derivatized Ru(bda) (4,4′-bpy)[2] (4,4′-bpy = 4,4′-bipyridine, 1) catalysts on the surfaces of a post-treated TiO2 layer on fluorine-doped tin oxide (FTO) (Fig. 1a)
Summary
Understanding and controlling the properties of water-splitting assemblies in dye-sensitized photoelectrosynthesis cells is a key to the exploitation of their properties. The dye-sensitized photoelectrosynthesis cell (DSPEC)[4,5,6], a molecular chromophore and catalyst are immobilized on wide bandgap, n-type semiconductors, such as fluorine-doped tin oxide (FTO), with a mesoporous TiO2 layer. Though stable in organic media, the stability of covalent binding in aqueous solution is largely dependent on external pH values because of potential hydrolysis at pH > 5 This undesirable hydrolysis results in the detachment of chromophore or catalyst from the metal oxide surface. Comparison with analogous phosphonate-derivatized [Ru(bpy)3]2+ complexes demonstrates improved surface stability in aqueous solution at pH 5 Another example was reported by the same group, where a pyridinederivatized platinum(II) porphyrin was used as an electrocatalyst for water reduction[21]
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