Insights into the transition metal ion-mediated electrooxidation of glucose in alkaline electrolyte

Glucose electrooxidation is of particular interest owing to its broad applications in glucose fuel cell and electrochemical sensing. In pursuit of high atomic utilization of catalytic active sites, we employed homogenously dispersed transition metal ions (Co ²⁺ , Cu ²⁺ , and Ni ²⁺ ) as the electrocatalyst in alkaline electrolyte. Combining cyclic voltammetry, chronoamperometry, impedance spectroscopy, and in situ UV–Vis spectroelectrochemistry, the catalytic activity and reaction mechanism of M(II)-catalyzed glucose electrooxidation are discussed, suggesting a general activity trend of Co(II) > Cu(II) > Ni(II). Using a μM level of Co(II), Cu(II), and Ni(II), the sensitivity values of 1,342, 579, and 38.9 mA M ⁻¹ cm ⁻² are achieved, respectively, toward glucose sensing. The coordination between metal sites and glucose plays the critical role of lowing the oxidation potential of M(II) to higher valent forms. A homogenous reaction mechanism is suggested: Co(II)-catalyzed reaction shows potential-dependent electrooxidation via the formation of Co(III)-glucose and Co(IV)-glucose complex, while both Cu(II) and Ni(II) feature the intermediate of M(III)-glucose. The Co(II)-glucose electrooxidation presents the smallest charge transfer resistance and the highest transfer coefficient, accounting for its high activity.