Enhanced Photoelectrochemical Water Splitting Using NiMoO₄/BiVO₄/Sn-Doped WO₃ Double Heterojunction Photoanodes

Efficient photoelectrochemical (PEC) water splitting systems in photoelectrodes are primarily challenged by electron–hole pair recombination. Constructing a heterostructure is an effective strategy to overcome this issue and to enhance PEC efficiency. In this study, we integrated NiMoO 4, known for its proper electrocatalytic conductivity, into a BiVO 4 /Sn-doped WO 3 heterojunction using solution-based hydrothermal and spin-coating methods, forming an innovative double heterojunction concept. The resulting NiMoO 4 /BiVO 4 /Sn:WO 3 triple-layer heterojunction photoanode exhibits a photocurrent density of 2.06 mA cm –2 in a potassium borate buffer (KBi) electrolyte at 1.23 V vs RHE, outperforming the bilayer BiVO 4 /Sn:WO 3 heterojunction (1.45 mA cm –2 ) and Sn:WO 3 photoanodes (0.55 mA cm –2 ) by approximately 1.4 and 3.7 times, respectively. Remarkably, the NiMoO 4 /BiVO 4 /Sn:WO 3 double heterojunction photoanode exhibits notable stability, showing only an approximate 30% reduction in initial photocurrent density after 10 h of measurement in the KBi electrolyte without a hole scavenger. This stability is attributed to the excellent corrosion resistance of the thin NiMoO 4 layer, effectively protecting the bilayer BiVO 4 /Sn:WO 3 heterojunction photoanode from photocorrosion. Our findings show how this novel double heterojunction, established through simple and cost-effective solution-based methods, offers a promising approach to enhancing PEC water splitting applications.