Intentional Extrinsic Doping into ZnFe2O4 Nanorod Photoanode for Enhanced Photoelectrochemical Water Splitting

Abstract

Zinc ferrite (ZnFe2O4) is a promising candidate photoanode material for photoelectrochemical water splitting, but its poor electronic properties deter it from achieving high performance. To improve the electronic properties, Ti4+ and Sn4+ are incorporated into Fe3+ sites of ZnFe2O4 as electron donors under annealing conditions of 550, 800 degrees C, or hybrid microwave annealing (HMA). The intentional external doping mainly promotes charge transport with increased charge carrier density and thereby enhances the bulk charge separation efficiency (eta(bulk)). Effectiveness of the doping varies with annealing conditions. Both Ti-doped and Sn-doped ZnFe2O4 annealed at 550 degrees C show the most significant improvement in eta(bulk) with little effect on the surface charge separation efficiency (eta(surface)). Doping under high-temperature annealing (800 degrees C, HMA) improves eta(bulk) to a lesser degree but creates a passivation layer of TiOx or SnOx, resulting in a higher eta(surface) as well. Finally, loading the NiFeOx oxygen evolution catalyst (OEC) further improves eta(surface) values, and especially 2% Ti-doped ZnFe2O4 annealed at 800 degrees C shows near 100% eta(surface) at 1.23 V-RHE, and its photocurrent generation under simulated 1 sun (0.312 mA cm(-2) at 1.23 V-RHE) represents a approximate to 18 times increment from that of unmodified ZnFe2O4 annealed at 550 degrees C.