Exploration of cobalt-based spinel oxide nanocatalysts MCo2O4 (M = Mn, Fe, Co, Ni, Cu, Zn) for glucose electrochemical sensing: NiCo2O4 exhibits largest Faradaic current

In traditional glucose sensing, glucose undergoes an enzyme-catalyzed oxidation reaction (GOR) on the electrode, causing electron transfer and generating a Faradaic current, which allows for quantitative glucose concentration analysis by measuring the current. Replacing enzymes with transition metal-based catalysts for glucose electrochemical sensing is a promising approach. As an extension of the study of spinel oxide Co3O4 for glucose electrochemical sensing, a series of cobalt-based spinel oxide nanocatalysts, MCo2O4 (M = Mn, Fe, Co, Ni, Cu, Zn), were prepared and studied. Their electrocatalytic oxidation activities for 3 mM glucose in 0.1 M KOH electrolyte solution (pH = 13) at potentials of 0.5 similar to 0.6 V (vs Hg/HgO) are in the order: NiCo2O4 > CuCo2O4 > MnCo2O4 > Co3O4 > FeCo2O4 > ZnCo2O4, the Faradic current by NiCo2O4 is more than three times that of Co3O4. When NiCo2O4 is loaded onto a carbon cloth electrode for glucose electrochemical sensing, it exhibits high linear sensitivity and stability. Furthermore, theoretical calculations revealed that the high electrocatalytic oxidation activity of NiCo2O4 for glucose is due to its effective reduction of the Gibbs free energy barrier for the desorption of intermediates to form glucose oxidation product. Finally, it is proposed that the electrocatalytic oxidation activities of MCo2O4 (M = Mn, Fe, Co, Ni, Cu, and Zn) towards glucose exhibit a "volcano plot" relationship with their d-band centers. This offers valuable guidance into using the d-band center as a descriptor to screen effective glucose electrocatalysts for glucose sensing and potentially other applications.