Design of continuous built-in band bending in self-supported CdS nanorod-based hierarchical architecture for efficient photoelectrochemical hydrogen production

The ever-increasing desire for clean and renewable energy has triggered the development of novel materials for photoelectrochemical (PEC) water splitting. However, elaborate design of photoanode materials with high light-harvesting capability, high charge-separation efficiency and long-term stability for converting solar energy into hydrogen fuel is highly challenged. Herein, we fabricated the self-supported gradient oxygen-doped three-dimensional (3D) CdS branched nanorod array (Grad-O CdS), in which a continuous built-in band bending structure was constructed by gradually oxygen doping. The kinetically-confined anion exchange under non-equilibrium condition was confirmed to be critical to achieve the gradient doping. The obtained Grad-O CdS exhibited a large photocurrent density of 6.0 ± 0.1   mA   cm −2 at 0.4   V vs. RHE , which could be maintained for over 42   h. Such excellent performance and stability can be attributed to the efficient separation of charge carriers, which benefits from its continuous built-in band bending caused by oxygen doping, and enhanced light-harvesting capability derived from the narrowing band gap and 3D hierarchical structure. This gradient doping strategy provides a valuable guideline for the design of efficient photoelectrode materials for the conversion of solar energy.