Promoting the photo-induced charge separation and photoelectrocatalytic hydrogen generation: Z-scheme configuration of WO3 quantum nanodots-decorated immobilized Ti/TiO2 nanorods

Highlights: • H₂ evolution reactions proceeded using TNRs-WQNDs as a noble metal-free photoanode. • The impact of WQNDs on optical and photoelectrochemical properties of TNRs was assessed. • Introduction of WQND using 10 mg WCl₄ remarkably boosted charge carriers generation. • Photoelectrocatalytic H₂ production by TNRs-WQNDs (10) was 1.7 times higher than TNRs. • The H₂ production using TNRs-WQNDs (10) photoanode followed the Z-scheme mechanism. -- Abstract: The photoelectrocatalytic hydrogen production, especially using 1D TiO₂ nanostructures, has been considered as a clean and sustainable approach to cope with energy crisis. Nevertheless, the large band gap energy of TiO₂ and the rapid photo-induced charges recombination have limited its practical application. Therefore, in this study, WO₃ quantum nanodots were employed with immobilized TiO₂ nanorod arrays (TNRs-WQNDs) to tackle these drawbacks. Based on the results, the incorporation of WQNDs ameliorated both the optical and photoelectrochemical properties of TNRs. In this relation, the introduction of WQNDs into TNRs lattice using 10 mg WCL₄ (TNRs-WQNDs (10)), as the optimum amount of tungsten precursor, not only made band gap energy much narrower (from 3 to 2.1 eV), but also significantly improved the photocurrent density from 0.92 to 1.67 mA/cm² (at 1.23 V vs. RHE). In addition, both the STH and photoconversion efficiencies of TNRs-WQNDs (10) were about 1.7 and 1.5 times more than those of pure TNRs, respectively. As a result of these enchantments, the coupling of WQNDs with TNRs was able to increase the photoelectrocatalytic hydrogen production from 1.4 to 2.4 mmol under UV irradiation. An acceptable photoelectrocatalytic performance was further observed under visible light irradiation, where TNRs-WQNDs (10) could generate almost 1.5 mmol of hydrogen. Meanwhile, by investigating the mechanism of photoelectrocatalytic hydrogen production, it was revealed that the reaction pathways over TNRs-WQNDs (10) conformed to the Z-scheme theory. Finally, the fifth incessant cycled test indicated that TNRs-WQNDs (10) photoanode had excellent chemical stability and low photo-corrosion ability.