A Charge-Transfer Switcher-Based Double S-Scheme Ternary Heterojunction toward Enhanced Photocatalytic H ₂ Evolution and H ₂ O ₂ Production

Upgrading from a single S-scheme to a double S-scheme heterojunction by inserting another semiconductor affords a challenging means of concurrently augmenting the charge-transfer dynamics and surface reaction kinetics while preserving extraordinary redox ability. Herein, a 2D Cu x Se y nanosheet is inserted between a 1D CoTiO 3 nanorod and 2D petals of a NiCo-LDH nanoflower to construct a double S-scheme CoTiO 3 /Cu x Se y /NiCo-LDH 1D/2D/2D ternary heterojunction through a combination of calcination and hydrothermal processes. In comparison to NiCo-LDH and CoTiO 3 /NiCo-LDH, the ternary hybrid exhibited 7.2 and 2.5 times higher H 2 evolution rates, respectively, and it also displayed a better H 2 O 2 production of 978 μmol h –1 g –1, which was 2.8, 2.1, and 1.6 times higher than those of CoTiO 3, NiCo-LDH, and the CoTiO 3 /NiCo-LDH nanohybrid, respectively. Further, it parades the conversion efficiencies of 9.1 and 0.013% for H 2 and H 2 O 2 production, respectively. The enhanced activities are due to the formation of a double S-scheme heterojunction, where Cu x Se y acts as a charge-transfer mode switcher. The Ni/Ti–Se bond at the dual interface of the ternary heterojunction served as a bridge for the effective separation of charge carriers. The double S-scheme charge transfer was validated by the scavenger experiment, work function, in situ XPS, and in situ KPFM analysis. This study provides a valuable understanding of the double S-scheme charge transfer with an increasing overall efficiency of the photoredox behavior.