Influence of ammonia on the conductivity of Nafion membranes

Abstract

The effect of NH 3 and NH 4 + poisoning on the conductivity of Nafion membranes was investigated via electrochemical impedance spectroscopy. The conductivities of membranes prepared with different NH 4 + compositions were measured in deionized water at room temperature and compared to those at 80 °C in a gas phase for various relative humidities. The liquid-phase conductivity decreased linearly with an increase in the NH 4 + composition in the membrane ( y N H 4 + ), with that of the NH 4 +-form having a conductivity 25% that of the H +-form. The gas-phase conductivity of the NH 4 +-form, on the other hand, declined by 66–98% relative to the H +-form depending on humidity. The conductivities of fresh membranes in the presence of gas-phase NH 3 at different humidities were also studied. The conductivity decreased with time-on-stream and reached the same conductivity at a given humidity regardless of the NH 3 concentration, but the time to reach steady-state varied with NH 3 concentration. The y N H 4 + at steady-state conductivity was equivalent for all the NH 3 concentrations studied. The kinetics of conductivity decrease was slower at higher humidities. The humidity and y N H 4 + appear to have a concerted effect on the conductivity. The quantitative conductivity data under practical fuel cell conditions should be useful for future fuel cell modeling.