Influence of vanadium doping on the supercapacitance performance of hexagonal birnessite

• V-doped birnessites are prepared by adding NH4VO3 to redox system of KMnO4 and HCl.
• Mn(IV) and K+ are partially substituted by V(V) in birnessite.
• Doping vanadium affects birnessite particle size and electrochemical properties.
• Doped birnessite (V/Mn = 0.14:1) exhibits a stable capacitance of 245 F g−1.

Nanostructured birnessite, promising candidate for supercapacitor electrode materials, shows greatly improved discharge capacity and cyclic stability with vanadium doping. The influence of vanadium doping on the physicochemical properties and supercapacitance performance of birnessite-type manganese oxides is investigated. Crystal structures, micromorphologies, bond lengths and chemical compositions of vanadium doped birnessites are characterized by XRD, SEM, XPS, TGA, and titration. The electrochemical properties are analyzed using galvanostatic charge–discharge test, cyclic voltammetry, and electrochemical impedance spectroscopy. The results exhibit that V/Mn molar ratio can reach 0.16:1 when Mn(IV) and K+ are partially substituted by V(V) in birnessite. The thickness of disk-shaped crystal, bond length of Mn–O1 and manganese average oxidation state decreases first and then increases with an increase in V/Mn molar ratio in synthesis system. Charge-transfer resistance decreases after doping vanadium, and increases with an increase in the content of vanadium in birnessite. Diffusion resistance increases first and then decreases due to the change of particle size and pore size distribution. The highest specific capacitance of 245 F g−1 is obtained with excellent cyclic stability for doped birnessite with V/Mn molar ratio of 0.14:1. Our study indicates that vanadium remarkably affects micromorphology, substructure, and electrochemical properties of manganese dioxides.

Vanadium doped birnessites are fabricated with partial substitution of Mn(IV) and K+ through the reduction of KMnO4 by concentrated hydrochloric acid with adding NH4VO3. The pseudocapacitance performance of nanostructured birnessites is greatly improved by doping vanadium due to the increase of surface area and the decrease of diffusion impedance.Figure optionsDownload as PowerPoint slide