Enhanced charge transfer with tuning surface state in hematite photoanode integrated by niobium and zirconium co-doping for efficient photoelectrochemical water splitting

Niobium and zirconium co-doping was introduced into a hematite (Fe2O3) photoanode by a facile two-step synthesis. The hydrothermally prepared zirconium-doped photoanode shows a reduction in the crystallite size of hematite, with H(104) being the dominant photoactive phase. The incorporation of niobium ions by drop -casting and high-temperature annealing does not alter the crystallinity. The core 3d spin-orbit splitting shows the Nb4+ oxidation state forming NbO2 in the hematite lattice. The Nb4+-Zr4+ co-doped hematite photoanode, prepared on a fluorine-tin oxide glass substrate, shows an enhanced photocurrent density of 2.05 mA cm(-2) with no co-catalyst. This enhanced performance is attributed to the Zr4+ doping, which improves the bulk charge transfer in hematite, and Nb4+ suppressed charge recombination in the surface state holes at the electro-de-electrolyte interface. This synergistic improvement of bulk and surface properties leads to stable water splitting at the water oxidation potential (1.23 VRHE) of the Nb-Zr co-doped hematite photoanode.