Gradient Built-In Electric Field Engineering in Hierarchical Co_0.85Se Quantum Dots-Modified Cadmium Sulfide Nanorods...

Efficient charge separation and durable cocatalyst interfaces are critical for advancing visible-light photocatalytic hydrogen production. Here, we develop an in situ selenization strategy that anchors defect-rich Co_0.85Se quantum dots onto CdS nanorods while simultaneously forming a Se-doped CdS surface layer, yielding a tightly coupled QDs-shell-core heterostructure. This construction establishes a spatial dual built-in electric field arising from Se-doping-induced band modulation and the Co_0.85Se/CdS interfacial junction, which strongly promotes directional electron transfer. Experimental characterizations and DFT calculations jointly reveal that the defect-rich Co_0.85Se QDs act as efficient electron sinks, accelerating H₂ evolution. Consequently, the optimized photocatalyst delivers a hydrogen evolution rate of 61.66 mmol g^-1 h^-1 with only 0.7 wt% Co_0.85Se loading, which is far exceeding pristine CdS and outperforming Pt/CdS and presents markedly enhanced photostability. This study offers a practical pathway for designing low-loading, non-noble-metal cocatalyst systems for high-performance solar hydrogen production.