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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

Oxygen reduction reaction catalyzed by epsilon-MnO2: Influence of the crystalline structure on the reaction mechanism

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Author(s):
Valim, R. B. [1] ; Santos, M. C. [2] ; Lanza, M. R. V. [1] ; Machado, S. A. S. [1] ; Lima, F. H. B. [1] ; Calegaro, M. L. [1]
Total Authors: 6
Affiliation:
[1] Univ Sao Paulo, Inst Quim Sao Carlos, BR-78013560 Sao Carlos, SP - Brazil
[2] Univ Fed ABC UFABC, CCNH, LEMN, BR-09210170 Santo Andre, SP - Brazil
Total Affiliations: 2
Document type: Journal article
Source: Electrochimica Acta; v. 85, p. 423-431, DEC 15 2012.
Web of Science Citations: 44
Abstract

The oxygen reduction reaction (ORR) was studied in KOH electrolyte on carbon supported epsilon-manganese dioxide (epsilon-MnO2/C). The epsilon-MnO2/C catalyst was prepared via thermal decomposition of manganese nitrate and carbon powder (Vulcan XC-72) mixtures. X-ray powder diffraction (XRD) measurements were performed in order to determine the crystalline structure of the resulting composite, while energy dispersive X-ray analysis (EDX) was used to evaluate the chemical composition of the synthesized material. The electrochemical studies were conducted using cyclic voltammetry (CV) and quasi-steady state polarization measurements carried out with an ultra thin layer rotating ring/disk electrode (RRDE) configuration. The electrocatalytic results obtained for 20% (w/w) Pt/C (E-TEK Inc., USA) and alpha-MnO2/C for the ORR, considered as one of the most active manganese oxide based catalyst for the ORR in alkaline media, were included for comparison. The RRDE results revealed that the ORR on the MnO2 catalysts proceeds preferentially through the complete 4e(-) reduction pathway via a 2 plus 2e(-) reduction process involving hydrogen peroxide as an intermediate. A benchmark close to the performance of 20% (w/w) Pt/C (E-TEK Inc., USA) was observed for the epsilon-MnO2/C material in the kinetic control region, superior to the performance of alpha-MnO2/C, but a higher amount of HO2- was obtained when epsilon-MnO2/C was used as catalyst. The higher production of hydrogen peroxide on epsilon-MnO2/C was related to the presence of structural defects, typical of this oxide, while the better catalytic performance in the kinetic control region compared to alpha-MnO2/C was related with the higher electrochemical activity for the proton insertion kinetics, which is a structure sensitive process. (C) 2012 Elsevier Ltd. All rights reserved. (AU)

FAPESP's process: 11/02158-5 - Evaluation of the electrocatalytic properties of pure and modified manganese oxides for the oxygen reduction reaction in alkaline solutions
Grantee:Marcelo Luiz Calegaro
Support Opportunities: Regular Research Grants