| Summary: | The development of efficient and novel p-n heterojunctions for photoelectrochemical (PEC) water splitting is still a challenging problem. We have demonstrated the complementary nature of (p-type) BiSbS<sub>3</sub> as a sensitizer when coupled with (n-type) TiO<sub>2</sub>/CdS to improve the photocatalytic activity and solar to hydrogen conversion efficiency. The as-prepared p-n heterojunction TiO<sub>2</sub>/CdS/BiSbS<sub>3</sub> exhibits good visible light harvesting capacity and high charge separation over the binary heterojunction, which are confirmed by photoluminescence (PL) and electrical impedance spectroscopy (EIS). The ternary heterojunction produces higher H<sub>2</sub> than the binary systems TiO<sub>2</sub>/CdS and TiO<sub>2</sub>/BiSbS<sub>3</sub>. This ternary heterojunction system displayed the highest photocurrent density of 5 mA·cm<sup>−2</sup> at 1.23 V vs. reversible hydrogen electrode (RHE) in neutral conditions, and STH of 3.8% at 0.52 V vs. RHE is observed. The improved photocatalytic response was due to the favorable energy band positions of CdS and BiSbS<sub>3</sub>. This study highlights the p-n junction made up of TiO<sub>2</sub>/CdS/BiSbS<sub>3</sub>, which promises efficient charge formation, separation, and suppression of charge recombination for improved PEC water splitting efficiency. Further, no appreciable loss of activity was observed for the photoanode over 2500 s. Band alignment and interfaces mechanisms have been studied as well.
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