Rational design of CdS@ZnO core-shell structure via atomic layer deposition for drastically enhanced photocatalytic H₂ evolution with excellent photostability

Photocatalytic H₂ evolution is highly attractive for converting abundant solar energy to valuable fuel. Herein, we report the use of an atomic layer deposition (ALD) technology to fabricate a new class of CdS@ZnO core-shell heterostructure. The rationally designed ultrathin ZnO shell not only allows the light to be absorbed by CdS core, but also provides an intimate heterojunction interface between ZnO shell and CdS core. The amount of ZnO shell coated on CdS core is finely tuned by the number of deposition cycles, and the obtained CdS@ZnO with 100 ALD deposition cycles displays the optimal photocatalytic H₂ evolution rate of 11.36 mmol/g/h. When Pt and PdS are used as the co-catalysts, the H₂ evolution rates are further enhanced to 71.39 and 98.82 mmol/g/h, respectively, which are 4.1 and 5.7 times higher than the highest reported value (17.40 mmol/g/h) among CdS-ZnO catalyst systems. Detailed characterization reveals that the drastically enhanced photocatalytic activity can be attributed to not only efficient space separation of the photo-induced electrons and holes resulted from the formation of a direct Z-scheme photocatalytic system between crystalline ZnO and CdS, but also the intimate contact at molecular scale between the two semiconductors. Due to the coverage of ALD-prepared crystalline ZnO shell on CdS core, the CdS@ZnO core-shell structures exhibit excellent photostability.