Bi-functional electrocatalytic systems for oxygen reduction in acid medium

Marta Ratter ,  Iwona A. Rutkowska ,  Krzysztof Miecznikowski ,  Beata Baranowska ,  Adam Lewera ,  Paweł J. Kulesza 

Warsaw University, Faculty of Chemistry, Pasteura 1, Warszawa 02-093, Poland

Abstract

Modification of carbon-supported RuSex nanoparticles or cobalt porphyrin catalytic centers with ultra-thin films of tungsten oxide results in the enhancement of their catalytic properties towards electroreduction of oxygen in acid (0.5 mol dm-3 H2SO4) medium as evidenced from the positive shift of the O2 reduction potential and the higher heterogeneous rate constant. An important issue is that the metal oxide support is characterized by good electronic conductivity and proton donating properties. Further, it is reasonable to expect that not only RuSex or cobalt porphyrin centers are reactive but also tungsten oxide support is capable of promoting the reduction of the undesirable hydrogen peroxide intermediate. For example, the bifunctional activity of the WO3-modified RuSex system has been the most pronounced at rather low loadings of RuSex nanoparticles. An important issue is tolerance of the proposed systems to methanol, ethanol or acetic acid formic acid, i.e. the organic systems that may appear due to crossover in the cathode compartments of methanol or ethanol fuel cells. Further, the WO3-modified RuSex (carbon-free) samples have been immobilized on the gold electrode surface for Synchrotron X-ray Photoelectron Spectroscopy (XPS) examination. The preliminary measurements have been carried out using excitation energies in the range from 90 to 1400 eV. Such experiments allow us to comment on the electronic modification of electron core levels caused by presence of adsorbed WO3 and to determine the amounts of WO3 present on the catalyst’s surface after contacting with aqueous media. These results show that the WO3 is not only adsorbed on catalyst’s surface but it also tends to interact electronically with RuSex catalytic centers. This phenomenon may also explain the relatively good stability of WO3 on the RuSex surface.

 

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Presentation: Poster at SMCBS'2007 International Workshop, by Marta Ratter
See On-line Journal of SMCBS'2007 International Workshop

Submitted: 2007-09-27 17:48
Revised:   2009-06-07 00:48