Core-double shell ZnO/ZnS@Co₃O₄ heterostructure as high performance pseudocapacitor

In recent times, a great deal of attention has been paid to the balanced design and fabrication of core-shell heterostructures for enhanced pseudocapacitor (SC) performance. In this paper, we report the synthesis of ZnO@Co₃O₄ based core-shell heterostructures with controllable shell thickness for the first time by a simple low-temperature solution-based method and their detailed electrode performance as SC wherein a highly enhanced pseudocapacitance of 296 C g^-1 at a current density of 0.5 A g^-1 has been observed. Further, modifying the surface of ZnO by its sulfur analogue (i.e., by creating a ZnO/ZnS heterostructure), an improved capacitance of 317 C g^-1 at a current density of 0.5 A g^-1 for ZnO/ZnS@Co₃O₄ has been obtained along with a better rate performance. This is attributed to an efficient charge transfer from ZnS to ZnO. Impressively, the core-double shell heterostructure exhibits high energy density of 36 Wh kg^-1 at a power density of 204.3 W kg^-1. Even at a very high power density of 10.9 kW kg^-1, it shows an energy density of 14.7 Wh kg^-1. To the best of our knowledge, this is the first study of the electrochemical properties of ZnO/ZnS@Co₃O₄ heterostructure.