EFFECTS OF BISMUTH(III)-OXIDE ON THE STRUCTURAL AND ELECTROCHEMICAL PROPERTIES OF PYROLUSITE (BETA-MNO2)

被引:10
作者
AXMANN, P [1 ]
GLEMSER, O [1 ]
机构
[1] UNIV GOTTINGEN,INST ANORGAN CHEM,TAMMANNSTR 4,D-37077 GOTTINGEN,GERMANY
来源
BERICHTE DER BUNSEN-GESELLSCHAFT-PHYSICAL CHEMISTRY CHEMICAL PHYSICS | 1993年 / 97卷 / 09期
关键词
DOPED MANGANESE DIOXIDE; ELECTROCHEMISTRY; SPECTROSCOPY; X-RAY;
D O I
10.1002/bbpc.19930970914
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Cycle-life and charge/discharge curves of pure and physically Bi2O3-doped pyrolusite (beta-MnO2) were studied. Crystalline intermediate products of the first three semi-cycles, give information about the effects of Bi2O3. A mechanism is postulated. In the first two semi cycles pyrolusite (beta-MnO2) is converted to the layered delta-MnO2 with beta-Mn(OH)2 in the fully discharged state. In the course of the following discharge hausmannite Mn3O4, which is electrochemically inert, is formed. No hausmannite is found in presence of Bi2O3. Pieces of information on mechanistical aspects can be gathered from the initial discharge process. During the initial discharge of beta-MnO2, delta-MnO2 is formed as an intermediate product. In the undoped case this species can be found around MnO1.75. In presence of Bi2O3, however, delta-MnO2 is existent nearly down to MnO1.25 over the whole discharge region. The reaction path diverges at the [Mn(III)(OH)4(H2O)2]- ion, dissoluted during the cycling process: in presence of Bi2O3 the reaction is controlled kinetically by a quick disproportionation of the [Mn(III)(OH)4(H2O)2]- ions resulting in 6-MnO2 and beta-Mn(OH)2. In absence of Bi2O3, thermodynamical control occurs, and [Mn(III)(OH)4(H2O)2]- reacts with [Mn(II)(OH)4(H2O)2]2 forming the electrochemical non-reactive hausmannite Mn3O4.
引用
收藏
页码:1147 / 1155
页数:9
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