Interfacial band alignment and photoelectrochemical properties of all-sputtered BiVO₄/FeNiO<i>_x</i> and BiVO₄/FeMnO<i>_x</i>p–n heterojunctions

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 FeMOx (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/FeMnOx 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/FeMOx (M = Ni, Mn) heterojunctions. Our results show that type II heterojunctions arise in the BiVO4/FeMOx (M = Ni, Mn) interface after equilibrium, thereby providing potential barriers to inhibit electron flow from the BiVO4 to the FeMOx layers. Furthermore, the BiVO4/FeMnOx film showed a larger space charge region (SCR) characterized by a more intense built-in electric field than BiVO4/FeNiOx, 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