Efficient photocatalytic overall water splitting by synergistically enhancing bulk charge separation and surface reaction kinetics in Co3O4–decorated ZnO@ZnS core-shell structures

Abstract

Due to hole capture effect of Co 3 O 4 and the existence of inner electric field built at the p–n junction interface as well as the presence of the core–shell heterojunction, the surface reaction kinetics and bulk charge separation can be greatly improved, resulting in an outstanding H 2 and O 2 production rates in the absence of sacrificial reagents. • The Co 3 O 4 /ZnO@ZnS composites were prepared from the Co-Zn bimetallic MOFs. • The p-n junction and core–shell structure can boost the bulk charge separation. • Co 3 O 4 was used as cocatalysts to facilitate the surface water oxidation. • The optimal H 2 and O 2 production rates reached up to 3853 and 1927 μmol g −1 h −1 . Spontaneously photocatalytic water splitting to generate H 2 and O 2 represents a promising strategy for converting solar energy to chemical energy. However, photocatalytic water splitting without sacrificial agents is difficult due to the poor bulk charge separation and retarded surface reaction kinetics. Herein, we first combined the p–type Co 3 O 4 cocatalysts with n–type ZnO@ZnS core–shell heterojunction to create a Co 3 O 4 –decorated ZnO@ZnS p–n junction by using bimetallic ZnCo–MOFs as template. In this hybrid, both the heterojunction and p–n junction can accelerate the bulk charge separation, while the highly dispersed Co 3 O 4 cocatalysts can enhance the surface reaction kinetics. As a result, the outstanding H 2 and O 2 production rates of 3853 and 1927 μmol g −1 h −1 were obtained for the optimal sample, approximately 1750, 550 and 110 times higher than those of ZnO, ZnO@ZnS and ZnO/Co 3 O 4 . Such synergistic enhancement can be evidenced by charge separation efficiency calculation. XAFS, XPS and DFT calculation indicated that the electrons and holes can be effectively assembled on ZnO and Co 3 O 4 , respectively. This work provides a new strategy for combining the advantages of cocatalyst and p–n junction as well as the core–shell heterojunction to enhance the photocatalytic water splitting without sacrificial agent.