Oxygen electrodes in fused salts Potentiometric behaviour of the system CO2, O2/CO32− in molten alkali nitrates

Abstract

A potentiometric study on the carbonate electrode (Pt or Au) CO2, O2/CO32− was performed at 523 and 623 K in a (Na−K)NO3 equimolar mixture containing carbonate in the concentration range 10−5<[CO32−]<10−2 M and maintained under flux of a mixture of oxygen and carbon dioxide at variable partial pressures (pO2+pCO2=1 atm.). While the overal electrode reaction for a carbonate electrode can be expressed by the equation12O2+CO2+2e=CO32−(a)the present study has shown that the potential taken up by an “indifferent electrode” can be described by the equationE=const.+(RT/2F)1n{[CO2]/[CO32−]}(b)The apparent potentiometrically irreversible behaviour of the carbonate electrode under the given experimental conditions has been interpreted on the basis of a mechanistic model involving, in the potential-determining step, the oxidized surface of the noble metals. For exampleDownload : Download full-size image