DEVELOPMENT OF ELECTROCHEMICAL SENSORS FOR HYDROGEN, OXYGEN, AND WATER USING PERFLUOROSULFONIC ACID MEMBRANES

The development of solid state potentiometric sensors for hydrogen and oxygen utilizing Nafion polymer electrolyte is described. The reference electrode comprises a mixture of Fe(II) and Fe(III) sulphate hydrates. For pure hydrogen at 1 atm. pressure, E(H)O = + 0.68V; for pure oxygen at 1 atm. pressure, E(O)O = - 0.36V. For hydrogen inert gas mixtures in the pressure range approximately 10(-4) < p(H) less-than-or-equal-to 1 atm, and for oxygen-inert gas mixtures in the pressure range approximately 10(-2) < p(O) less-than-or-equal-to 1 atm, Nernstian response is observed. For mixtures of hydrogen, oxygen and an inert gas, a mixed potential is observed which is a linear function of the ratio of the pressures of hydro-en and oxygen over the range approximately 0.25 < p(H)/p(O) < approximately 10.0. The sensor is also responsive to hydrogen introduced into steel e.g. by a corrosion reaction. The elapsed time between the initiation of the corrosion reaction on the inner surface of a steel vessel and detection of hydrogen by the sensor at the outer surface permits estimation of the diffusion coefficient of hydrogen in steel approximately 2 x 10(-6) cm2/s at ambient temperature. Data on water sorption by Nafion, the diffusion coefficient of water in Nafion and the electrical conductivity of Nafion are presented. Nafion absorbs approximately 14 mols H2O/mol H+ when equilibrated with water at unit activity. The diffusion coefficient of water is a strong function of the water content. The electrical conductivity is also a strong function of the water content. This latter dependency is exploited in the development of an amperometric sensor for water vapour in gases.