Optimizing hydrogen evolution performance through balancing charge dynamics across sulfur-defect-engineered CdIn₂S₄-NC/MoC heterojunctions

Designing efficient photocatalysts with heterojunctions is key to enhancing photocatalysis. Ignoring surface states hinders understanding of heterojunction performance, and balancing charge dynamics is crucial for optimizing photocatalytic hydrogen evolution (PHE) activity. We fabricated a Schottky junction composite featuring a dual-metal system, which consists of sulfur-defect-engineered CdIn₂S₄ (CIS) combined with a hollow N-doped carbon (NC)-anchored MoC heterojunction. The optimal CdIn₂S₄/NC/MoC (25CIS-CM) composite achieves a remarkable 58.2-fold enhancement in PHE rate compared to bare CIS under visible illumination. In-situ femtosecond transient absorption (fs-TA) measurements has shown that some thermalized electrons get trapped by shallow defects on the surface in pure CIS about 24.342 ps, while others transition into inter-bandgap trap states, exhibiting a relaxation time τ₃ of approximately 282.207 ps. As the CM loading increases, τ₃ gradually decreases (282.207 ps → 160.820 ps → 72.471 ps → 61.33 ps). And most higher loading of CM (50CIS-CM) results in a faster photogenerated carrier recombination time (τ₄ = 2861.46 ps), ultimately causing a diminished rate for 50CIS-CM during PHE. The balance between charge trapping at shallow and deep energy levels, carrier interfacial migration, and band-edge recombination deepens our understanding of the photocatalytic mechanism of CIS-based heterojunctions and ultimately promoting the rapid development of green energy technologies.