A dye sensitized photosynthesis cell for stable water oxidation mediated by photo-generated bromine

Abstract

The critical step of a dye-sensitized photoelectrochemical cell (DSPEC) is water oxidation. The photoanodes suffer rapid surface carrier recombination due to slow water oxidation kinetics and this results in low solar conversion efficiency and poor stability. Here, we design a novel sensitization–oxidation photo-anode, where the [Ru(4,4′-PO₃H₂-bpy)(bpy)₂]²⁺ (RuP²⁺, bpy = 2,2′-bipyridine) chromophore and [Ru(bda)(pic)₂] (pic = picoline, bda = 2,2′-bipyridine-6,6′-dicarboxylate) water oxidation catalyst (WOC) are immobilized separately on the surface of a mesoporous semiconductor thin film. The electrode creates a mobile and strong Br₃⁻ oxidant generated by the dye-sensitized electrode, which initiates water oxidation at a remote catalytic site. Under 100 mW cm⁻² illumination in pH 4.65 in 0.1 M acetate buffer solution, the photoanode could perform a stable photoelectrochemical water oxidation for 6 hours with a photocurrent density of around 0.25 mA cm⁻². This dual electrode could open a new door by utilizing an electron transfer mediator to design highly stable photoelectrochemical cells.