Redox preparation of mixed-valence cobalt manganese oxide nanostructured materials: highly efficient noble metal-free electrocatalysts for sensing hydrogen peroxide

Abstract

High-performance hydrogen peroxide sensors provide valuable signals of biological interactions, disorders, and developing of diseases. Low-cost metal oxides are promising alternatives but suffer from low conductivity and sensing activity. Multi-component metal oxides are excellent candidates to accomplish these challenges, but the composition inhomogeneity is difficult to manage with conventional material preparation. We demonstrated redox preparation strategies to successfully synthesize highly homogeneous, noble metal-free H₂O₂ sensors of spinel nanostructured cobalt manganese oxides with enhanced conductivity, multiple mixed-valence features, and efficient H₂O₂ sensing activities. The designed redox reactions accompanied with material nucleation/formation are the key factors for compositional homogeneity. High conductivity (1.5 × 10⁻² S cm⁻¹) and H₂O₂ sensing activity (12 times higher than commercial Co₃O₄) were achieved due to the homogeneous multiple mixed-valence systems of Co(II)/(III) and Mn(III)/(IV). A wide linear detection range (from 0.1 to 25 mM) with a detection limit of 15 μM was observed. Manganese species assist the formation of large surface area nanostructures, enhancing the H₂O₂ reduction activities, and inhibit the sensing interference. The material controls of hierarchical nanostructures, elemental compositions, porosity, and electrochemical performances are highly associated with the reaction temperatures. The temperature-dependent properties and nanostructure formation mechanisms based on a reaction rate competition are proposed.