Oxygen electrodes in fused salts: Investigation and mechanistic remarks on the system (Ni)O2, H2O/OH− in the (Na,K)NO3 eutectic melt |
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Authors: | Basilio Morelli Luigia Sabbatini Pier Giorgio Zambonin |
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Institution: | Istituto di Chimica Analitica, Università di Bari, Via Amendola, 173, 70126-Bari Italy |
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Abstract: | A potentiometric investigation on the system (Ni)O2, H2O/OH? was carried out within the temperature range 513?T?636 K in the (Na, K)NO3 equimolar mixture containing OH? ions in the concentration range 5×10?6<OH?]<10?1m and flushed with a mixture of O2 and H2O at variable partial pressures. The system has been found to behave reversibly in all hydroxide concentration and temperature intervals studied with respect to all the species involved in the over-all electrode reaction ½ O2+H2O+2e?=2OH? so that the following nernstian relationship could be written E=EO2,H2O/OH?+RT/Fln{O2]1/4H2O]1/2/OH?]} This potentiometric behaviour was tentatively interpreted on the basis of mechanistic models involving, in some steps, solid nickel oxides formed on the electrode surface by contact with the melt. The actual formation and existence of these compounds on the electrode surface under the given experimental conditions was proved by a proper XPS investigation. |
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