Synthesis of Tungsten Trioxide/Hematite Core-Shell Nanoarrays for Efficient Photoelectrochemical Water Splitting

Hematite, with a band gap of 2.0∼2.2 eV suitable for visible light absorption, has emerged to be a promising photoanode material for photoelectrochemical (PEC) catalysis of the oxygen evolution reaction (OER). Herein, we proposed the design and fabrication of a WO₃/α-Fe₂O₃ core-shell heterojunction structure, aiming at alleviating the severe mismatch between the relatively long light penetration depth and the extremely short holes diffusion length in α-Fe₂O₃. The WO₃ nanoarray underlayer is grown directly on the FTO substrate, serving as an effective electron transfer layer and additional light absorber. The α-Fe₂O₃ layer is further prepared via spin-coating and a subsequent calcination process as a thin and uniform shell. The loading amount was regulated with different spin coating times of the precursor. The optimized WO₃/α-Fe₂O₃ core-shell nanoarrays display an excellent performance with lower onset potential of 0.65 V vs. RHE and increased photocurrent response of 1.29 mA cm⁻² at 1.23 V vs. RHE, much superior than the pristine α-Fe₂O₃ or WO₃ photoanode. Characterizations demonstrate that both improved light absorption and formation of heterojunction account for the excellent performance. After coating a NiFe-LDH co-catalyst layer, the oxygen evolution reaction is further enhanced, and high stability is achieved, benefiting from the efficient charge carrier generation, promoted charge separation in the semiconductor and the rapid consumption of holes for surface reaction.