Awakening inert CoAl₂O₄ for nonenzymatic glucose sensing by shifting Co from tetrahedral to octahedral sites

A facile calcination temperature awakens inert CoAl 2 O 4 for nonenzymatic glucose sensing. • Partial inversion creates octahedral Co sites that generate high valent active species. • Tetrahedral Co in normal spinel shows negligible glucose electrooxidation activity. • The awakened sensor delivers competitive sensitivity and reliable real sample analysis. Activating intrinsically inert tetrahedral cobalt in spinel oxides for non-enzymatic glucose sensing remains a challenge, since octahedrally coordinated cobalt is known to readily generate active high-valent species whereas its tetrahedral counterpart stays largely inactive. Herein we demonstrate that the intrinsically inactive spinel CoAl₂O₄ can be effectively activated for glucose electrooxidation via a simple calcination temperature strategy. A Co Al gel precursor calcined at 500 °C (CoAl₂O₄-500°) yields a partially inverse spinel with a fraction of cobalt occupying octahedral sites, while the same precursor calcined at 800 °C forms a normal spinel (CoAl₂O₄-800°) with cobalt confined to tetrahedral sites. CoAl₂O₄-500° exhibits strong electrocatalytic activity toward glucose oxidation, whereas CoAl₂O₄-800° remains nearly inert. Consequently, the sensor fabricated from CoAl₂O₄-500° exhibits outstanding sensitivity of 722 μA mM −1  cm −2 , a wide linear range from 0.4 μM to 0.222 mM, and a low detection limit of 0.13 μM. This work establishes that engineering cation site occupancy can effectively activate dormant spinel oxides, thus offering a generalizable design strategy for advanced non-enzymatic electrochemical sensors. Shifting cobalt from tetrahedral to octahedral sites awakens inert CoAl₂O₄ for non-enzymatic glucose sensing. Download: Download high-res image (117KB) Download: Download full-size image