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 NiMoO₄, known for its proper electrocatalytic conductivity, into a BiVO₄/Sn-doped WO₃ heterojunction using solution-based hydrothermal and spin-coating methods, forming an innovative double heterojunction concept. The resulting NiMoO₄/BiVO₄/Sn:WO₃ 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 BiVO₄/Sn:WO₃ heterojunction (1.45 mA cm^-2) and Sn:WO₃ photoanodes (0.55 mA cm^-2) by approximately 1.4 and 3.7 times, respectively. Remarkably, the NiMoO₄/BiVO₄/Sn:WO₃ 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 NiMoO₄ layer, effectively protecting the bilayer BiVO₄/Sn:WO₃ 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.