Proton Conductivity of Nafion 117 as Measured by a Four‐Electrode AC Impedance Method

Abstract

The proton conductivity of Nafion 117 was measured under various conditions of humidity and temperature usin a four-electrode ac impedance method. The conductivity of this membrane without heat-treatment was ca. 7.8 X 10 S cm' at ambient temperature and 100% relative humidity; it varied strongly with the humidity and heat-treatment of the membrane. After heat-treatment, the membrane showed a slight dependence of conductivity on temperature. From 21 to 45°C, its conductivity at a given relative humidity decreased with increasing temperature, while from 45 to 80°C it increased with temperature.Nafion 117® is a proton conducting ion-exchange membrane which is now receiving much attention due to its use as an electrolyte in the polymer-electrolyte-membrane fuel cell (PEMFC), which is of great interest for electric vehicle propulsion.' The performance of the PEMFC is strongly dependent on the humidification of the membrane, since membrane resistance changes drastically with water content. The water balance of the fuel cell is also extremely complicated. During the cell reaction in the PEMFC, the anode side (fuel side) of the membrane is readily dried up by the electro-osmotic drag of the proton, while the water produced in the cathode reaction diffuses back to the anode side. Analysis of the performance of a PEMFC requires reliable conductivity data for the membrane electrolyte at different humidities in combination with water uptake,4-1 water diffusion,8 gas diffusion properties,914 etc.

Proton conducting composite membranes from polyether ether ketone and heteropolyacids for fuel cell applications

“…The other factors, including the polymer intrinsic conductivity, strength, density and softness of the solid acid sites, the solid phase loading, particle size and spatial distribution, the aqueous phase dispersion, all affect the dependence of conductivity on the water content. In the case of Nafion membranes which are described as nanoporous inert 'sponges' for water of hydration, this water shows little interaction with the polymer chain and forms hydration shells around the sulfonic acid groups [26]. In HPA/SPEEK composite membranes, the aqueous phase is more continuous.…”

Development of imidazolium-type alkaline anion exchange membranes for fuel cell application

“…This was done quickly to minimize the potential error caused by reaction of the hydroxide ions in the AAEM with dissolved carbon dioxide (resulting in the formation of carbonate/bicarbonate anions and reduced AAEM conductivity). The ionic conductivity was calculated according to the following equation: 38 RWd L = κ where R is the membrane resistance, L is the distance between potential sensing electrodes, and W and d are the width (here 1 cm) and thickness of the membrane respectively. All samples were equilibrated in water for 24 h prior to conductivity measurements.…”

Alkali resistant and conductive guanidinium-based anion-exchange membranes for alkaline polymer electrolyte fuel cells

“…The ionic conductivities of the GPPO-X AAEMs were measured using the commonly encountered four-point probe technique [21]. The Teflon measuring cell consisted of two stainless steel flat outer current-carrying electrodes (spacing = 2 cm) and two platinum wire inner potential-sensing electrodes (spacing = 1 cm).…”