3D nanoporous core-shell ZnO@Co₃O₄ electrode materials for high-performance supercapacitors and nonenzymatic glucose sensors

Transition metal oxides have excellent electrochemical activity and properties because of the various valence states, high electrical conductivity, and ample active sites. In this study, a composite electrode comprising Co₃O₄ nanowire arrays and ultrathin and porous ZnO nanoflake films is formed by a simple hydrothermal method and pulsed electrodeposition. In this unique three-dimensional (3D) nanoporous core–shell ZnO@Co₃O₄ heterojunction, the Co₃O₄ nanowire arrays in the core with good electrical conductivity and porous ZnO nanosheets in the shell synergistically increase the active sites, expedite mass transfer, and improve the structural stability. The ZnO@Co₃O₄ sensor detects glucose selectively as manifested by a short amperometric response time of 3 s while delivering excellent performance such as a wide dynamic linear range (0.001–18.917 mM), low detection limit (0.0426 µM), and high sensitivity (4082.1 µA µM⁻¹ cm⁻²). The ZnO@Co₃O₄ structure is also suitable for supercapacitors as it shows a high specific capacitance of 1618.26 F g⁻¹ at a current density of 10 A g⁻¹, excellent rate performance (retention of 97.1 % up to 10 A g⁻¹), and long cycling stability (91.23% retention for 5,000 cycles). These remarkable properties confirm the feasibility of the materials design and the ZnO@Co₃O₄ structure has large potential as multi-functional materials in electrochemical sensing and energy storage.