Composite Based on Multi-Walled Carbon Nanotubes and Manganese Oxide with Rhenium Additive for Supercapacitors: Structural and Electrochemical Studies

The structure and electrochemical characteristics of composites based on multi-walled carbon nanotubes (MWCNTs) and manganese oxide with the addition of rhenium oxide has been studied. It has shown that the decorating of the MWCNT surface with layers or nanoparticles of manganese oxide (Mn(III) + Mn(IV)) provides more than a twofold increase in the value of the specific capacitance at low potential scan rates. However, composites based only on manganese oxide exhibit poor electrochemical behavior and the value of the specific capacitance decreases rapidly with increasing potential scan rate due to the limitation of diffusion processes. The addition of rhenium oxide to composites significantly increases their electrochemical properties due to changes in the chemical composition and morphology of composites. Studies of the structure and chemical state have shown that an improvement in the specific capacitance is provided by increasing in the proportion of Mn(IV) oxide in such composites, which has the ability to rapidly and completely reverse redox reactions and has lower electrical resistance values, compared to Mn(III) oxide. A detailed analysis of the voltammetric data showed that an increase in the rate capability in composites with the addition of rhenium oxide can also be provided by increasing the availability of the electrode surface for electrolyte ions and increasing the amount of charge stored due to the formation of a double electric layer.