BiVO4 charge transfer control by a water-insoluble iron complex for solar water oxidation

Photoelectrochemical water splitting can become efficient by grafting co-catalysts on semiconductors that improve the interfacial oxygen evolution reaction. We applied a simple non-noble metal pre-catalyst, [FeII(PBI)3]2+ (PBI is 2-(2′-pyridyl)benzimidazole ligand) for this purpose on a nanopyramidal BiVO4 semiconductor that was morphologically optimal for efficient light harvesting, but its performance suffered from V-poor surface recombination sites. The [FeII(PBI)3]2+in situ transformed to α-Fe2O3 nanoparticles on V-vacant areas of BiVO4 mending their photocurrent-limiting effect. Photoelectrochemistry at pH 8.2 confirmed that the α-Fe2O3 co-catalyst improved the charge transfer efficiency by an order of magnitude, suppressed the recombination in the bulk and reduced the charge transfer resistance. Overall, the α-Fe2O3 suppressed the recombination on the V-poor surface, while at high potentials it provided high-valent centers for the oxygen evolution. The resulting photocurrent density far exceeding that of BiVO4 or samples modified by FeCl3 or Fe(NO3)3 underlines the metallochaperone-like effect of the PBI ligand. [Display omitted] •BiVO4 nanopyramids modified using a molecular Fe pre-catalyst for water oxidation.•in situ formed nano-α-Fe2O3 bind selectively at V-vacant sites of the photoanode.•at high potentials, the co-catalyst favors the kinetics of oxygen evolution reaction.•at low potentials, the surface hole recombination is reduced by α-Fe2O3.