Spinel CuCo₂O₄ Microflowers with Highly Exposed High-Index (112) Facets for Electrocatalytic Glucose Oxidation

The design of nanomaterials enclosed by high-index facets plays a critical role in the surface-sensitive properties. Herein, hierarchical CuCo₂O₄ microflowers (CCO-F) with highly exposed high-index (112) facets are rationally designed via a solvothermal method followed by calcination. CCO-F are composed of 30 nm-thick nanoflakes and have an ultrahigh specific surface area of ca. 205.48 m² g^-1. Additionally, nanoparticle-assembled CuCo₂O₄ microspheres (CCO-S) are prepared, and these nanoparticles are partly enclosed by the (110) facets. Abundant octahedrally coordinated Co³⁺ (Co³⁺_Oh) and tetrahedrally coordinated Cu²⁺ (Cu²⁺_Td) exist in the (112) facet, especially Co³⁺_Oh (with a density of 0.063 Å^-2); moreover, the (112) facet possesses a high surface Gibbs free energy (2.7367 J m^-2). Therefore, CCO-F have significant advantages of adsorbing glucose and conducting the subsequent redox reactions. In addition, the hierarchical microstructure promotes the reaction kinetics of CCO-F. Benefiting from these features, the CCO-F-modified electrode exhibits high sensitivities (1351.2 and 598.7 μA mM^-1 cm^-2), wide linear ranges (1 μM-3 mM and 4-10 mM), rapid response time, low detection limit, excellent stability, and good selectivity. This work indicates that the exposure of a high percentage of high-index facets is an effective approach to exploring high-performance electrocatalysts for glucose detection.