Strategic Assembly of MoSe₂@CdSe–ZnO Heterojunctions for Dual-Mode Photocatalytic and Photo/Electrocatalytic Hydrogen Production

Probing earth-abundant catalytic systems with multiple functionalities, remarkable activity, and robust stability is pivotal to sustainable H₂ production. Developing these catalytic systems not only mitigates cost and scalability challenges but also improves overall efficiency by enhancing charge separation, accelerating redox kinetics, and strengthening structural durability under operational conditions. In this quest, S-scheme MoSe₂@CdSe–ZnO heterojunctions have been designed hydrothermally to examine photochemical (PC), electrochemical (EC), and photoelectrochemical (PEC) activity for H₂ production. 1, 2.5, and 5 wt % MoSe₂@CdSe–ZnO (1CMZ, 2.5CMZ, and 5CMZ) photocatalytic systems showed significantly higher PC performance than pure ZnO, exhibiting the optimum 3.67 mmol g_cat^–1h^–1 H₂ generation with an apparent quantum yield (AQY) of 28.9% (450 nm). The MoSe₂@CdSe–ZnO catalytic system is designed as a ternary heterostructure with a uniform hexagonal phase to minimize lattice mismatch, reduce interfacial defects, and enhance charge carrier mobility, ultimately boosting the photocatalytic efficiency of MoSe₂@CdSe–ZnO for water splitting. EC experiments revealed the phenomenal HER and OER performances of optimized 2.5CMZ, showing low overpotential values of 970 and 310 mV, respectively. PEC results validated the supremacy of 2.5CMZ as the photocurrent density and overpotential values are enhanced compared to electrochemical outputs. Density functional theory, band structure analysis, time-resolved photoluminescence, electrochemical impedance spectroscopy, and ex situ X-ray photoelectron spectroscopy investigations deduced the robust relation between theoretical outputs and experimental results in establishing an S-scheme reaction mechanism.