Photoelectrocatalytic H₂ evolution from integrated photocatalysts adsorbed on NiO

A new approach to increasing the faradaic efficiency of dye-sensitised photocathodes for H₂ evolution from water, using integrated photocatalysts, furnished with ester groups on the peripheral ligands, [Ru(decb)₂(bpt)PdCl(H₂O)](PF₆)₂ (1) and [Ru(decb)₂(2,5-bpp)PtI(CH₃CN)](PF₆)₂ (2), (decb = 4,4'-diethylcarboxy-2,2'-bipyridine, bpp = 2,2':5',2''-terpyridine, bpt = 3,5-bis(2-pyridyl)-1,2,4-triazole) is described. Overall, 1|NiO is superior to previously reported photocathodes, producing photocurrent densities of 30-35 μA cm^-2 at an applied bias of -0.2 V vs. Ag/AgCl over 1 hour of continuous white light irradiation, resulting in the generation of 0.41 μmol h^-1 cm^-2 of H₂ with faradaic efficiencies of up to 90%. Furthermore, surface analysis of the photocathodes before and after photoelectrocatalysis revealed that the ruthenium bipyridyl chromophore and Pd catalytic centre (1) were photochemically stable, highlighting the benefits of the approach towards robust, hybrid solar-to-fuel devices.