Surface-oxidized titanium diboride as cocatalyst on hematite photoanode for solar water splitting

Abstract

One of the key objectives for the hematite photoanode is to accelerate the kinetics of oxidative water splitting and inhibit the recombination of electron and hole. Here, we report a titanium boride (TiB₂)-modified hematite (α-Fe₂O₃) photoanode produced by spin coating and subsequent calcination; a surface oxidized layer is formed during this process. The photocurrent density of the surface-oxidized TiB₂ on α-Fe₂O₃ (α-Fe₂O₃/SO-TiB₂) photoanode [at 1.23 V versus reversible hydrogen electrode (vs. RHE), 2.0 mA cm⁻²] is observably increased compared to α-Fe₂O₃ (at 1.23 vs. RHE, 0.57 mA cm⁻²). In addition, the SO-TiB₂-decorated heterogeneous junction hematite (HJ-Fe₂O₃/SO-TiB₂) has greater photocurrent activity (at 1.23 vs. RHE, 2.5 mA cm⁻²). This improvement of the photoelectrochemical (PEC) property is due to the formation of a surface oxide layer, which regulates the direction of the interface electric field, improving improves the separation and injection efficiency of photogenerated charges, as proved by photophysical characterization and PEC measurements. Thereby, the water oxidation kinetics for the α-Fe₂O₃-based photoanode are significantly accelerated.