Anodic deposition of manganese oxide electrodes with rod-like structures for application as electrochemical capacitors

A review of electrode materials for electrochemical supercapacitors

“…[268][269][270][271][272] Since the early report by Lee and Goodenough in 1999, 273 MnO x has attracted major attention and is considered a promising alternative class of materials for ES applications. 45,195,[274][275][276][277] The capacitance of manganese oxides comes mainly from pseudocapacitance, which is attributed to reversible redox transitions involving the exchange of protons and/or cations with the electrolyte, as well as the transitions between Mn(III)/ Mn(II), Mn(IV)/Mn(III), and Mn(VI)/Mn(IV) within the electrode potential window of the electrolyte. 278,279 The proposed mechanism is expressed in eqn (14) (14) suggests that both protons and alkali cations are involved in the redox process, and that the MnO x material must have high ionic and electronic conductivity.…”

“…Thus, the morphology of MnO 2 plays a determinant role in its electrochemical performance. 45,301 In the literature, prepared manganese oxides have many different morphologies, such as nanowires, [302][303][304] and flower-like nanowhiskers. 292 Depending on the morphology, the obtained material's specific surface area can range from 20 to 150 m 2 g À1 .…”

“…For example, using a soft template method, various morphologies are obtainable by adjusting the precursors and conditions. 309 Using an anodic deposition method, 45 the morphology of manganese oxide prepared from manganese acetate solutions is controllable by varying the deposition current density. In a hydrothermal reaction, the morphology of MnO 2 changes by varying the reaction time at a given molar ratio of reactants, the solvent used, the temperature of the reaction, and so forth.…”

“…The third morphology is an Mn oxide film with a rodlike structure (prepared through anodic deposition from a 0.01 M Mn acetate solution at various deposition current densities on Au-coated Si substrates), whose maximum capacitance is 185 F g À1 . 45 The fourth is a petalshaped manganese oxide, which may not be a good choice for ES material because it could reduce the specific surface area, leading to capacitance fading. Further, the more ordered hexagonal NiAs-type crystal structure possesses fewer electrochemically active sites available for fast ionic transport and charge transfer.…”

The specific capacitance of sol–gel synthesised spinel MnCo2O4 in an alkaline electrolyte

“…Generally, Mn oxides have relatively 41 low specific capacitance and partial dissolution in alkaline elec-42 trolyte also leads to decay in capacitance [9][10][11]. Besides, Mn oxides 43 have a poor electronic [12] and ionic conductivity [13,14]. Recently, 44 researchers find that binary metal oxides are quite intriguing 45 from the perspectives of both fundamental science and technology 46 because the composite can enable versatile and tailor-made prop-47 erties with performances far beyond those of monometallic oxides 48 [15].…”