Pseudocapacitive properties of carbon nanotube/manganese oxide electrode deposited by electrophoretic deposition

Nanocrystalline manganese oxide powder prepared by spray pyrolysis (SP) was mixed with multi-walled carbon nanotubes (MWCNTs) in a suspension and subsequently co-coated onto graphite substrates via an electrophoretic deposition technique (EPD). The deposited coatings with or without CNTs mix were examined by X-ray diffractometry (XRD); the coatings were examined by cycling voltammetry (CV) and charge/discharge tests. Structural investigation by XRD revealed that the as-deposited Mn-oxide powder exhibited Mn₃O₄ phase with nanocrystalline structure. The CNTs/Mn-oxide coatings exhibited a porous structure with some hollow or fractured Mn-oxide particles inserted and possessed a high surface area for the electrochemical redox reactions. CV examination showed that the porous CNTs/Mn-oxide coatings exhibited the high specific capacitance of 260 F/g which was higher than the value (234 F/g) of Mn-oxide coatings without CNTs mix at a scan rate of 25 mV/s. After 500 cycles of CV tests, the specific capacitance decreased to 228 F/g, showing a comparatively good efficiency of 88%. The high CV cycling stability of CNTs/Mn-oxide mixture is due to the fact that the CNTs network existent in between the Mn-oxide particles inhibits the structural breakdown of Mn-oxide particles during the repetitive insertion-expulsion of cations from aqueous electrolyte.