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Reply to the comment by lamy et al.
Elecwochimica Acta, Vol. 35. No Printed in Great Britain.
3, p. 681.
1990.
00134686/90 13.00 f0.00 Ct.1 1990. Pergamon Pressplc
REPLY TO THE COMMENT
BY LAMY et al.
A. HEINZEL,* R. HOLZE, C. H. HAMANN and J. K. BLUM~ *Fraunhofer-Institut fur Solare Energieforschung, Oltmannsstr. 22, D-7800 Freiburg, F.R.G. tuniversitat
Oldenburg, Fachbereich Physik, Carl-von-Ossietzky-Str.
9-l 1, D-2900 Oldenburg, F.R.G.
(Received 12 June 1989)
The comment by Lamy et aI.[l] on our recent report [2] contains, besides a selective collection of experimental results predominantly by Lamy et al., some minor statements concerning our work which we
would like to clarify. Obviously adsorbed CO seems to be the poisoning adsorbed species on a platinum electrode severely disturbing the methanol oxidation, nevertheless its formation from methanol may proceed through various intermediates which include according to our results a paramagnetic formyl species. We are well aware of the fact, that the electrode potential applied in our work necessary to form the spin trap in situ is higher than electrode potentials useful in fuel cells, therefore we did not claim that our results will explain processes occurring in fuel cell electrodes at the respective electrode potentials. In addition we have indicated a second part of our work which indeed deals with similar electrooxidation processes occurring at lower electrode potentials[3]. The particular selectivity of spectroelectrochemical methods is well known to discerning electrochemists, although the literature contains example which are proof of the contrary. We are well aware of the consequences of our experimental approach, but cannot see any possibility of avoiding the problem pointed out by Lamy et al. when using a spin trap. The same reasoning must consequently be applied to other results, too. It seems likely, that vibrational spectroscopy applied to electrochemical in situ investigations allows the preferred detection of species with a very high absorp-
tion coefficient and adsorbed in preferred orientations. Other adsorbed species may thus escape detection. We cannot see a contradiction between our results and those reported by Lamy et al. Besides the fact, that still the controversy concerning the chemical nature of the poisoning intermediate is not settled completely, we only intended to demonstrate the radical nature of reaction intermediates. We did not claim this intermediate to be the strongly adsorbed electrode poison. The calculation of the ESR spectrum shown in Fig. 4c [Z] was done assuming a linewidth of 0.037 mT, the two spectra calculated with the parameters listed in [2] were added with weighing factors of 0;75 for adduct I and of 1.0 for adduct II. g Values could not be determined since the spectroelectrochemical cell excluded the use of a field strength detector in the ESR spectrometer. These experimental details do not affect the interpretation and discussion of our results.
REFERENCES C. Lamy, B. Beden and J. M. Leger, Electrochim. Acta 35, 679 (1990). A. Heinzel, R. Holze, C. H. Hamann and J. K. Blum, Electrochim. Acta 34, 657 (1989). A. Heinzel, R. Holze, C. H. Hamann and J. K. Blum, 2. phys. Chem. NT., 160, 11 (1988).
681
3, p. 681.
1990.
00134686/90 13.00 f0.00 Ct.1 1990. Pergamon Pressplc
REPLY TO THE COMMENT
BY LAMY et al.
A. HEINZEL,* R. HOLZE, C. H. HAMANN and J. K. BLUM~ *Fraunhofer-Institut fur Solare Energieforschung, Oltmannsstr. 22, D-7800 Freiburg, F.R.G. tuniversitat
Oldenburg, Fachbereich Physik, Carl-von-Ossietzky-Str.
9-l 1, D-2900 Oldenburg, F.R.G.
(Received 12 June 1989)
The comment by Lamy et aI.[l] on our recent report [2] contains, besides a selective collection of experimental results predominantly by Lamy et al., some minor statements concerning our work which we
would like to clarify. Obviously adsorbed CO seems to be the poisoning adsorbed species on a platinum electrode severely disturbing the methanol oxidation, nevertheless its formation from methanol may proceed through various intermediates which include according to our results a paramagnetic formyl species. We are well aware of the fact, that the electrode potential applied in our work necessary to form the spin trap in situ is higher than electrode potentials useful in fuel cells, therefore we did not claim that our results will explain processes occurring in fuel cell electrodes at the respective electrode potentials. In addition we have indicated a second part of our work which indeed deals with similar electrooxidation processes occurring at lower electrode potentials[3]. The particular selectivity of spectroelectrochemical methods is well known to discerning electrochemists, although the literature contains example which are proof of the contrary. We are well aware of the consequences of our experimental approach, but cannot see any possibility of avoiding the problem pointed out by Lamy et al. when using a spin trap. The same reasoning must consequently be applied to other results, too. It seems likely, that vibrational spectroscopy applied to electrochemical in situ investigations allows the preferred detection of species with a very high absorp-
tion coefficient and adsorbed in preferred orientations. Other adsorbed species may thus escape detection. We cannot see a contradiction between our results and those reported by Lamy et al. Besides the fact, that still the controversy concerning the chemical nature of the poisoning intermediate is not settled completely, we only intended to demonstrate the radical nature of reaction intermediates. We did not claim this intermediate to be the strongly adsorbed electrode poison. The calculation of the ESR spectrum shown in Fig. 4c [Z] was done assuming a linewidth of 0.037 mT, the two spectra calculated with the parameters listed in [2] were added with weighing factors of 0;75 for adduct I and of 1.0 for adduct II. g Values could not be determined since the spectroelectrochemical cell excluded the use of a field strength detector in the ESR spectrometer. These experimental details do not affect the interpretation and discussion of our results.
REFERENCES C. Lamy, B. Beden and J. M. Leger, Electrochim. Acta 35, 679 (1990). A. Heinzel, R. Holze, C. H. Hamann and J. K. Blum, Electrochim. Acta 34, 657 (1989). A. Heinzel, R. Holze, C. H. Hamann and J. K. Blum, 2. phys. Chem. NT., 160, 11 (1988).
681