Interfacial band alignment and photoelectrochemical properties of all-sputtered BiVO4/FeNiOx and BiVO4/FeMnOx p–n heterojunctions

Abstract

BiVO₄ is a well-known n-type semiconductor with great potential for photoelectrochemical (PEC) conversion of solar energy into chemical fuels. Nevertheless, photocurrent densities achieved for bare BiVO₄ photoanodes are still far from their theoretical maximum due to the sluggish water oxidation kinetics and limitation in electron-hole recombination. In this work, magnetron sputtering deposition was used for depositing FeMO_x (M = Ni, Mn) as cocatalyst layers to induce p–n heterojunctions and suppress charge recombination on BiVO₄ photoanodes. The all-sputtered p–n heterojunction BiVO₄/FeMnO_x exhibited the highest photocurrent density (1.25 mA cm⁻² at 1.23 V vs. RHE) and excellent chemical stability, indicating that the combination of Mn sites on Fe-based oxides provides promising cocatalytic materials for PEC applications. Experimental and theoretical techniques were used to investigate the interfacial band alignment and charge transport properties of BiVO₄/FeMO_x (M = Ni, Mn) heterojunctions. Our results show that type II heterojunctions arise in the BiVO₄/FeMO_x (M = Ni, Mn) interface after equilibrium, thereby providing potential barriers to inhibit electron flow from the BiVO₄ to the FeMO_x layers. Furthermore, the BiVO₄/FeMnO_x film showed a larger space charge region (SCR) characterized by a more intense built-in electric field than BiVO₄/FeNiO_x, explaining its higher PEC performance. In summary, this work provides a viable technique for producing photocatalytic heterojunction systems based on metal oxide semiconductors and introduces simple tools for investigating interface effects on photoinduced charge carrier pathways for PEC applications.