Rational design of stratified material with spatially separated catalytic sites as an efficient overall water-splitting photocatalyst

The development of metal sulfide catalysts with remarkable activity toward efficient overall photocatalytic water splitting remains challenging owing to the dominant charge recombination and deficient catalytic active sites. Moreover, in the process of water oxidation catalysis, the inhibition of severe photocorrosion is an immense task, requiring effective photogenic hole-transfer kinetics. Herein, stratified Co-MnO2@CdS/CoS hollow cubes with spatially separated catalytic sites were rationally designed and fabricated as highly efficient controllable catalysts for photocatalytic overall water splitting. The unique self-templated method, including a continuous anion/cation-exchange reaction, integrates a Co-doped oxidation co-catalyst (Co-MnO2) and a reduction co-catalyst (CoS) on the nanocubes with uniform interface contact and ultrathin two-dimensional (2D) nanometer sheets. We demonstrate that the stratified Co-MnO2@CdS/CoS hollow cubes can provide an abundance of active sites for surface redox reactions and contribute to the separation and migration of the photoionization charge carriers. In particular, CoS nanoparticles dispersed on the walls of CdS hollow cubes were identified as reduction co-catalysts accelerating hydrogen generation, while Co-MnO2 nanosheets attached to the inner walls of the CdS hollow cube were oxidation co-catalysts, promoting oxygen evolution dynamics. Benefiting from the desirable structural and compositional advantages, optimized stratification of Co-MnO2@CdS/CoS nanocubes provided a catalytic system devoid of precious metals, which exhibited a remarkable overall photocatalytic water-splitting rate (735.4 (H2) and 361.1 (O2) μmol h−1 g−1), being among the highest values reported thus far for CdS-based catalysts. Moreover, an apparent quantum efficiency (AQE) of 1.32% was achieved for hydrogen evolution at 420 nm. This study emphasizes the importance of rational design on the structure and composition of photocatalysts for overall water splitting.