Highly sensitive H₂O₂ sensor based on Co₃O₄ hollow sphere prepared via a template-free method

Graphical abstract: High-activity nanoscale Co₃O₄ hollow sphere has been developed using cobalt-containing imidazolate MOF framework ZIF-67 as precursor. The obtained cobalt oxide exhibited excellent electrocatalytic ability toward H₂O₂, with a high sensitivity, a low detection limit, a broad linear sensing range, and a short response time. - Highlights: • Co-MOF ZIF-67 nanocrystals were synthesized by coordination modulation method. • Co₃O₄ hollow spheres were prepared by pyrolysis of ZIF-67. • The obtained Co₃O₄ own the high density of active metal sites. • Co₃O₄ modified electrode could effectively detect H₂O₂. • The sensor showed high sensitivity, low detection limit, and broad linear range. - Abstract: Hollow-sphere Co₃O₄ nanoparticles were successfully synthesized by direct pyrolysis of cobalt-containing zeolitic imidazolate frameworks (ZIF-67) precursor. The transformation process from ZIF-67 to Co₃O₄ hollow sphere was characterized by powder X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and thermal gravimetric analysis. It is found that the as-prepared Co₃O₄ nanoparticles possesses uniform hollow spherical structure with many voids on the surface. It's worth noting that the high density of metal sites, the ordered arrangement of Co, as well as the uniform crystal size and regular morphology was inherited from ZIF-67, resulting in an excellent accessibility of Co. The resulting Co₃O₄ hollow sphere was exploited as an electrocatalyst for sensitive H₂O₂ detection in an alkaline medium. The Co₃O₄ hollow sphere modified glassy carbon electrode exhibited a fast response time (within 3s), a high sensitivity of 120.55 μA/mM (959.79 μA∙mM⁻¹∙cm⁻¹), a broad linear range from 0.4 μM to 2.2 mM, a detection limit of 0.105 μM (S/N=3), and good stability and selectivity, suggesting its excellent performance towards H₂O₂ detection.