Oxygen vacancy enriched hollow cobaltosic oxide frames with ultrathin walls for efficient energy storage and biosensing

Transition metal oxides (TMOs) with desired morphologies and atomic structures have promising applications in energy storage, catalysis, and biosensing because of their large specific surface area, high theoretical capacitance, abundant active sites, etc. In this study, hierarchical Co₃O₄ with enriched oxygen vacancies and finely tuned nanostructures, e.g. high porosity, thin wall thickness, hollow or yolk-shell structure, is prepared by dynamically balancing the decomposition and oxidation of the zeolitic imidazolate framework-67 (ZIF-67) precursor directly calcined in air at 300 °C. The optimized Co₃O₄ hollow frame inherits the original shape of the parent ZIF-67 with a high volume retention of 83% and features an ultrathin wall thickness of 10 nm, a large accessible surface area of 63.7 m² g^-1 and a high content of surface oxygen vacancies. It thus delivers an excellent specific capacitance of 770 F g^-1 at 1 A g^-1, a rate capability of 570.9 F g^-1 at 20 A g^-1 and excellent cycling stability for energy storage, and a high sensitivity of 0.7 mA mM^-1 cm^-2, a low detection limit of 0.2 μM (S/N = 3), and a wide linear detectable range of 0.005-1.175 mM for electrochemical non-enzymatic detection of glucose.