Electronic Structure Engineering of Cu-Mn Spinel Oxides via Ni Substitution for Enhanced Electrocatalytic Glucose...

Diabetes is one of the major civilization diseases of the 21st century. Effective glucose monitoring is a crucial diagnostic method for its active prevention. In addition to widely used enzyme-based sensors, nonenzymatic sensing solutions are being actively developed. The highest sensing performance has been reported for cobalt-containing compounds (i.e., Co₃O₄), but certain challenges related to availability and cost necessitate the search for alternative materials. The paper presents the electrocatalytic performance of nickel-doped manganese-copper spinel oxides for glucose detection in aqueous solutions. The spinel oxides were doped with nickel in various mass ratios: CuMn₂O₄, CuMn_2‑x Ni-( _{x = 0.3,0.6,0.9})-O₄. Structural analysis was performed to determine their crystalline properties, and the influence of the nickel content on the electrocatalytic activity was systematically investigated. It was found that the amount of nickel significantly affected the sensing properties of the synthesized powders. The most active samples exhibited a sensitivity of approximately 695 μA mM^-1 cm^-2 in the linearity range of 0.02-0.1 mM and 406 μA mM^-1 cm^-2 in the range of 0.2-1 mM. Electrochemical measurements were further extended to determine selectivity for commonly occurring interfering compounds. Additionally, operando X-ray absorption spectroscopy was used to monitor changes in the oxidation states of electrochemically active elements during the glucose oxidation reaction. Theoretical density of states confirmed that nickel doping enhances glucose adsorption and improves the material's catalytic properties. This work revealed that the Mn³⁺/Mn⁴⁺ redox pair acts as the dominant electroactive center during glucose oxidation, whereas nickel primarily functions as an electronic structure modulator, stabilizing Mn⁴⁺-rich surface species. The combined operando and theoretical analyses show how Ni addition influences glucose adsorption, charge transfer, and electrocatalytic glucose oxidation in Mn-based spinel oxides.