Kinetically and Thermodynamically Favorable Ni-Al Layered Double Hydroxide/Ni-Doped ZnCdS S-Scheme Heterojunction Triggering Photocatalytic H Evolution.

Layered double hydroxide (LDH)-based photocatalysts have attracted more attention in photocatalysis due to their low cost, wide band gaps, and adjustable photocatalytic active sites; however, their low photogenerated carrier separation efficiency limits their photocatalytic efficiency. Herein, a NiAl-LDH/Ni-doped ZnCdS (LDH/Ni-ZCS) S-scheme heterojunction is rationally designed and constructed from kinetically and thermodynamically favorable angles. The 15% LDH/1% Ni-ZCS displays comparable photocatalytic hydrogen evolution (PHE) activity with a rate of 6584.0 μmol g h, which exceeds by ∼6.14- and ∼1.73-fold those of ZCS and 1% Ni-ZCS, respectively, and outperforms most of the previously reported LDH-based and metal sulfide-based photocatalysts. In addition, the apparent quantum yield of 15% LDH/1% Ni-ZCS reaches 12.1% at 420 nm. X-ray photoelectron spectroscopy, photodeposition, and theoretical calculation reveal the specific transfer path of photogenerated carriers. On this basis, we propose the possible photocatalytic mechanism. The fabrication of the S-scheme heterojunction not only accelerates the separation of photogenerated carriers but also decreases the activation energy of H evolution and improves the redox capacity. Moreover, there are huge amounts of hydroxyl groups distributed on the surface of photocatalysts, which is highly polar and easy to combine with HO with a large dielectric constant to form a hydrogen bond, which can further accelerate PHE.