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 (Fe 2 O 3 ) 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 3 d spin-orbit splitting shows the Nb 4+ oxidation state forming NbO 2 in the hematite lattice. The Nb 4+ –Zr 4+ 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 Zr 4+ doping, which improves the bulk charge transfer in hematite, and Nb 4+ suppressed charge recombination in the surface state holes at the electrode–electrolyte interface. This synergistic improvement of bulk and surface properties leads to stable water splitting at the water oxidation potential (1.23 V RHE ) of the Nb–Zr co-doped hematite photoanode. • Nb–Zr:Fe 2 O 3 /FTO photoanode was synthesized via facile dual elemental co-doping. • A remarkable J ph of 2.05 mA cm −2 at 1.23 V RHE has been obtained without catalyst support. • Zr-doping promotes fast transfer of photogenerated electrons within bulk hematite. • Nb-doping boosting the surface charge (holes) injection efficiency at the SEI. • Synergistic effect of dual elemental co-doping promotes hole transfer via surface states.