Abrupt change with surfactant concentration in the surface morphology of the electrodeposited manganese oxide films for electrochemical capacitors

Manganese oxide films are produced by electrodeposition on a graphite sheet from a solution of manganese oxide with tetradecyltrimethylammonium bromide (TTAB) added as a surfactant. Effects of TTAB concentration on electrochemical and morphological properties of the films are observed. Under the bath conditions used in this work, the specific capacitance of the electrodeposited manganese oxide films has a maximum value of 343 F/g for TTAB concentration of 0.01 M. Change in the specific capacitance of the films with TTAB concentration is found to be associated with corresponding changes in the surface morphology of the films at those concentrations. Addition of TTAB up to 0.01 M is observed to increase the surface area of electrodeposited manganese oxide films, as the surface of the films is well covered with flake-like or petal-shaped arrays of nanofibers forming a three-dimensional network. Higher concentrations of TTAB than 0.01 M reduce the surface area of the films due to agglomeration and collapse of the nanofibers. The addition of 0.01 M TTAB to an electrochemical bath also improves supercapacitor capability such as rate capability, cycling stability, and electrode series resistance.