Fe₂O₃ Nanoflakes - WS₂ Nanosheets Heterojunctions for Multi-Fold Enhancement in Photoelectrochemical Solar Energy Conversion

Fe₂O₃-based photoanodes show great potential in photoelectrochemical water splitting due to their excellent stability, moderate band gap, and abundance. However, a short hole diffusion length limits its photocurrent density. Here, a multi-fold enhancement in photocurrent density from Fe₂O₃ nanoflakes - WS₂ nanosheets heterojunction is reported. The heterojunction exhibits a synergistic photocurrent density of 0.52 mA cm^-2 at 1.3 V (versus RHE) under AM 1.5G simulated sunlight, which is 2.23 times higher than pristine Fe₂O₃ nanoflakes. The Mott-Schottky and Nyquist plots indicate a higher charge density with lower charge transfer resistance at the semiconductor-electrolyte junction. The density functional theory (DFT) -based first-principles calculations are performed by designing a heterostructure between Fe₂O₃(110) and WS₂(001) similar to the experimentally found arrangement of crystal planes. Free energy analysis and relative band extrema positions, obtained from DFT calculations and valence band spectroscopy, indicate the formation of type II heterojunction with partial oxygen terminated surface of Fe₂O₃. The type-II band alignment with a charge transfer of 4.8 × 10^-4 e per interfacial WS₂ to Fe₂O₃, helps in easy separation of photogenerated charges. The work establishes both an experimental design and a theoretical framework of highly crystalline nanoflakes-nanosheet heterojunctions for efficient photoelectrochemical solar energy conversion.