Conductivity of Nafion® 117 membrane used in polymer electrolyte fuel cells

Abstract

The membrane electric transport (MC) directly influences the performance of the polymer electrolyte fuel cells (PEMFC). The membrane conductivity is determined by a number of parameters such as: hydration technique, graphite cell geometry and pressure applied when the membrane electrode assembly (MEA) is joined. In addition, the membrane conductivity might be influenced by the electrode position due to the possibility of anisotropic electric conductivity.This paper describes the technique used to measure the normal conductivity of Nafion® 117 applying direct current (DC). The membrane was previously hydrated with two different acid techniques. These two conditioning protocols have identical thermal treatments, the only difference is the acid utilized in each technique. The first treatment involved Nitric Acid while the second one was developed using Sulfuric Acid. The results obtained with the different treatments allowed us to identify the difference in the conductivity, issue that could not be appreciated when we studied only the degree of hydration of the membrane because the quantity of water molecules per sulfonic group was the same using both acids.The conductivity was measured using directly carbon paper/membrane/carbon paper samples fully immersed in deionized water. Carbon papers were previously painted with different graphite inks that allowed us to analyze the results and select the best one.The cell used for measuring conductivity was built with two graphite plates, copper connectors and conductive silver epoxy glue that allowed us to form a device similar to the one proposed in the literature. The results are reproducible and consistent with the published data.