Construction of Al‐STO/Zn _x Cd _1‐x S Type‐I High‐Low Junction for Enhanced Photocatalytic Hydrogen Evolution

ABSTRACT

Constructing heterojunctions is pivotal for enhancing photocatalytic charge separation, yet conventional type‐I architectures suffer from severe redox potential loss and rapid charge recombination. Here, we overcome this intrinsic limitation by developing a reduction‐state type‐I high‐low junction based on a composite of Al‐doped SrTiO ₃ (Al‐STO) and Zn _x Cd _1‐x S (Z0.6CS). The optimized SZ0.6‐20 heterojunction delivers a remarkable hydrogen evolution rate of 2857 µmol·g ⁻¹ ·h ⁻¹ without any noble‐metal cocatalyst, which further increases to 21154 µmol·g ⁻¹ ·h ⁻¹ with Pt as a co‐catalyst. Mechanistic investigations reveal that the large work‐function difference (ΔΦ = 1.3 eV) between Al‐STO and Z0.6CS induces a strong built‐in electric field and upward band bending on the Al‐STO side. This unique interfacial architecture selectively drives photogenerated holes from Al‐STO to Z0.6CS while blocking electron transfer, thereby preserving highly reductive electrons on the Al‐STO conduction band—a functionality unattainable in conventional type‐I junctions. This work not only provides a high‐performance photocatalyst for sustainable hydrogen production but also establishes the high‐low junction as a new design paradigm for straddling‐gap heterojunctions, decoupling carrier separation from redox potential compromise.