Enhanced Photoelectrochemical\nWater Splitting Using\nNiMoO<sub>4</sub>/BiVO<sub>4</sub>/Sn-Doped WO<sub>3</sub> Double\nHeterojunction Photoanodes

Efficient photoelectrochemical (PEC) water splitting\nsystems in\nphotoelectrodes are primarily challenged by electron–hole pair\nrecombination. Constructing a heterostructure is an effective strategy\nto overcome this issue and to enhance PEC efficiency. In this study,\nwe integrated NiMoO<sub>4</sub>, known for its proper electrocatalytic\nconductivity, into a BiVO<sub>4</sub>/Sn-doped WO<sub>3</sub> heterojunction\nusing solution-based hydrothermal and spin-coating methods, forming\nan innovative double heterojunction concept. The resulting NiMoO<sub>4</sub>/BiVO<sub>4</sub>/Sn:WO<sub>3</sub> triple-layer heterojunction\nphotoanode exhibits a photocurrent density of 2.06 mA cm<sup>–2</sup> in a potassium borate buffer (KBi) electrolyte at 1.23 V vs RHE,\noutperforming the bilayer BiVO<sub>4</sub>/Sn:WO<sub>3</sub> heterojunction\n(1.45 mA cm<sup>–2</sup>) and Sn:WO<sub>3</sub> photoanodes\n(0.55 mA cm<sup>–2</sup>) by approximately 1.4 and 3.7 times,\nrespectively. Remarkably, the NiMoO<sub>4</sub>/BiVO<sub>4</sub>/Sn:WO<sub>3</sub> double heterojunction photoanode exhibits notable stability,\nshowing only an approximate 30% reduction in initial photocurrent\ndensity after 10 h of measurement in the KBi electrolyte without a\nhole scavenger. This stability is attributed to the excellent corrosion\nresistance of the thin NiMoO<sub>4</sub> layer, effectively protecting\nthe bilayer BiVO<sub>4</sub>/Sn:WO<sub>3</sub> heterojunction photoanode\nfrom photocorrosion. Our findings show how this novel double heterojunction,\nestablished through simple and cost-effective solution-based methods,\noffers a promising approach to enhancing PEC water splitting applications.