Experimental study on critical role of heterostructures for efficient water splitting activity

Abstract

Water splitting has the potential to generate sustainable energy through the production of green hydrogen. Metal oxides are a preferred choice for semiconductor materials in photoelectrochemical (PEC) water splitting due to their stable performance in aqueous environments, cost-effectiveness, and ease of synthesis. However, individual metal oxides have certain limitations that can be addressed through heterostructure photoelectrodes. In this study, the performance of various heterostructure metal oxides, including BiVO₄, Fe₂O₃, Co₃O₄, and WO₃ was investigated under similar synthesis and testing conditions. These heterostructures were selected based on their band straddling properties and multi-junction concepts, which enable efficient utilization of the solar spectrum and enhance charge carrier separation. Six distinct heterostructures (FTO/WO₃/BiVO₄, FTO/Fe₂O₃/BiVO₄, FTO/WO₃/Fe₂O₃, FTO/WO₃/Co₃O₄, FTO/BiVO₄/Co₃O₄, FTO/Fe₂O₃/Co₃O₄) were evaluated with a focus on optimizing band alignment for efficient charge separation and PEC performance. Larger area electrodes (4 cm²) were synthesized and tested to ensure reliable performance metrics and eliminate edge effects observed in smaller electrodes. Among the studied heterostructures, WO₃/BiVO₄ heterostructure achieved the highest photocurrent density (1.68 mA/cm²), while Fe₂O₃/Co₃O₄ exhibited the highest dark current density (4.95 mA/cm²). Stability tests demonstrated the robustness of these heterostructures, with FTO/WO₃/BiVO₄ showing a minimal ∼ 5 % photocurrent degradation over 100 h of continuous operation. Structural (XRD, XPS), optical (UV–Vis), and electrochemical (EIS, Mott-Schottky) analyses provided comprehensive insights into the superior PEC performance of these heterostructures.