Light-driven water splitting was achieved using a dye-sensitized mesoporous oxide film and the oxidation of bromide (Br- ) to bromine (Br2 ) or tribromide (Br3- ). The chemical oxidant (Br2 or Br3- ) is formed during illumination at the photoanode and used as a sacrificial oxidant to drive a water oxidation catalyst (WOC), here demonstrated using [Ru(bda)(pic)2 ], (1; pic=picoline, bda=2,2'-bipyridine-6,6'-dicarboxylate). The photochemical oxidation of bromide produces a chemical oxidant with a potential of 1.09 V vs. NHE for the Br2 /Br- couple or 1.05 V vs. NHE for the Br3- /Br- couple, which is sufficient to drive water oxidation at 1 (RuV/IV ≈1.0 V vs. NHE at pH 5.6). At pH 5.6, using a 0.2 m acetate buffer containing 40 mm LiBr and the [Ru(4,4'-PO3 H2 -bpy)(bpy)2 ]2+ (RuP2+ , bpy=2,2'-bipyridine) chromophore dye on a SnO2 /TiO2 core-shell electrode resulted in a photocurrent density of around 1.2 mA cm-2 under approximately 1 Sun illumination and a Faradaic efficiency upon addition of 1 of 77 % for oxygen evolution.
Keywords: energy storage; photochemistry; photoelectrochemistry; water oxidation; water splitting.
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