Phase-controlled synthesis of polymorphic MnO₂ structures for electrochemical energy storage

Abstract

Manganese dioxide (MnO 2 ) with a-, b-and d-type structures was controllably synthesized by hydrothermal treatment of an acidic solution of KMnO 4 containing different concentrations of ions at 160 C. The effects of metallic cations, H + and anions on the structures and morphologies of MnO 2 were investigated systematically. The experimental results indicated that cations played a significant part in the formation of MnO 2 with different structures. When K + ions were in competition with H + ions in solution, different MnO 2 structures were formed. a-MnO 2 was formed when the amount of K + was higher than the amount of H + , whereas a higher amount of H + was favorable for the growth of b-MnO 2 structures. When the concentration of K + was much greater than that of H + , d-MnO 2 was obtained. Possible formation mechanisms are proposed based on a series of controlled experiments. The electrochemical properties of supercapacitors based on different types of MnO 2 electrodes were investigated in detail. The specific capacitance measured for MnO 2 strongly depended on the crystallographic structure and decreased in the order a-MnO 2 > d-MnO 2 > b-MnO 2 at a current density of 0.5 A g À1 . A specific capacitance of 535 F g À1 was obtained for a-MnO 2 , but was only 155 F g À1 for b-MnO 2 . a-MnO 2 was more suitable for use as the working electrode at high current densities. Both a-and d-MnO 2 had a poor cycling performance after 3000 cycles, whereas b-MnO 2 showed good stability, maintaining a cycling efficiency of 80% after under the same conditions.

On the Supercapacitive Behaviour of Anodic Porous WO3-Based Negative Electrodes

“…The use of pseudocapacitive materials, such as transition metal oxides and conducting polymers [12][13][14][15], instead of carbon based materials, leads to enhanced energy density without significant loss of power density. This enhancement results from the additive effect of fast superficial redox reactions and electric double layer formation at the electrode/electrolyte interface.…”

Urea-assisted hydrothermal synthesis of manganese dioxides with various morphologies for hybrid supercapacitors

“…Therefore, the morphologies of α-MnO 2 samples in our work were different from the nanospheres/nanosheets or nanorods reported in M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT the references [34,35].…”

“…Cheng et al [34] prepared α-MnO 2 nanospheres/nanosheets in KMnO 4 -H 2 SO 4 reaction system at 160 °C for 10h. Yin et al [35] successfully synthesized different MnO 2 structures by controlling the concentration of K + and H + in KMnO 4 -HNO 3 reaction system at 160 °C for 24h. The results indicated that β-MnO 2 particles were obtained when H + ions was more than K + ions; and α-MnO 2 nanorods were formed when K + ions was more than H + ions.…”

Functionalized-MnO 2 /chitosan nanocomposites: A promising adsorbent for the removal of lead ions

“…Recently, manganese dioxide (MnO 2 ) has attracted considerable attention because of their catalysis, molecular sieves and electrodes in rechargeable batteries, owing to their excellent electrochemical performance, low cost, nonpoisonous nature, environmental friendliness, and convenient preparation (Athouël, Moser, Dugas, Crosnier, Bélanger & Brousse, 2008;Qu et al, 2009;Tang, Meng & Huang, 2014;Zhang et al, 2012;Zhang et al, 2011). The MnO 2 has many polymorphic forms (α, β, γ and δ) (Kim et al, 2007;Yin, Zhang, Jiang, Qu & Wu, 2015;Zeng, Wang, Yang & Zhang, 2010;Zhu, Li, Deng & Liu, 2010). The α-MnO 2 has a hollandite-type structure including double chains of [MnO 6 ] octahedra forming 2 × 2 tunnels (Li, Pan, Chen & Li, 2007;Su, Ahn & Wang, 2013).…”