Cation‐Vacancy Model for MnO2

Abstract

A cation‐vacancy model for electrochemically active manganese dioxides ( γ‐MnO2 and ε‐MnO2 ) is presented. According to this model, the crystal structure, composed of closely packed O2− ions which are octahedrically coordinated to Mn4+ ions, the false[MnO6false] octahedra sharing edges and corners, contains Mn vacancies. Each vacancy is coordinated to, and electrostatically compensated by, four protons. The protons are present in the form of OH− ions, these latter replacing O2− in the lattice, without noticeable change in lattice parameters. Many hitherto unexplained phenomenological and experimental facts, relating to chemical composition (water content), density, electrochemical capacity, proton‐transfer rate, electronic conductivity, and electrode potential of MnO2 , can be reconciled, and quantitatively predicted, on the basis of the present theory. In particular, electrochemical reactivity of MnO2 in battery electrodes is shown to be due to the presence of cation vacancies in the lattice.

Electrodeposition of manganese dioxide: effect of quaternary amines

“…The absorption band at 1,100 cm −1 can be attributed to the MnO 2 stretching mode and/or O-H bending vibrations [35] associated with hydrogen bonding, indicating the presence of bound water molecules [32,33]. The strong absorption band at ∼1,630 cm −1 can be attributed to O-H bending vibrations associated with the water of crystallization [32] and a broad absorption band at ∼3,400 cm −1 is due to O-H stretching vibrations [32][33][34]. A weak absorption band is observed at ∼1,400 cm −1 indicating O-H stretching vibrations [36].…”

“…The presence of OH -groups and water molecules associated as bound water within the crystal structure can influence the electrochemical activity of the EMD [32][33][34]. For the sake of simplicity, the EMD sample prepared in the presence of 50 ppm organic additive was selected for all physical characterization (other than XRD, by which all samples were analyzed).…”

“…This mechanism is attributed to the reversible conversion of MnO 2 into MnOOH in the solid phase. The second electron discharge of MnO 2 , which proceeds either in solid or in solution phase, leads to the formation of Mn(OH) 2 , a product formed during recharging of γ-MnO 2 [34]. The typical discharge characteristics of the pellets made from EMD powders prepared from aqueous sulfate solutions in the absence and presence of organic additives TEAB, TPAB, and TBAB are shown in Figs.…”

Determinação de manganês em material particulado atmosférico de ambientes de trabalho utilizando eletrodo de diamante dopado com boro e voltametria de onda quadrada com redissolução catódica

“…a adição de próton mostrada na reação 7, proposta por Ruetschi 33,34 . Logo, o MnOOH obtido na reação 7 é isomorfo com MnO 2 .…”

“…Logo, o MnOOH obtido na reação 7 é isomorfo com MnO 2 . Além disso, Ruetschi 33,34 sugere que a adsorção e o transporte de íons H + na fase sólida controlam a redução de MnO 2 .…”