Aminated Perfluorosulfonic Acid Ionomers to Improve the Triple Phase Boundary Region in Anion-Exchange Membrane Fuel Cells

Abstract

We propose an approach to improve the triple phase boundary (TPB) of catalyst layers in anion-exchange membrane fuel cells by using aminated Nafion ionomers with amine molecules of ethylenediamine (EDA) and diethylenetriamine (DETA) as anion conductor. Aminated Nafion ionomers were characterized and clarified by Fourier transform IR spectroscopy, Raman spectroscopy, and transference number measurements. The transference number of the aminated Nafion ionomers with DETA (DETA-modified Nafion, t- =0.89) was larger than that of the EDA-modified Nafion (t- =0.81). Pt/C catalyst layers with EDA- and DETA-modified Nafion ionomers were constructed, and their oxygen reduction currents were evaluated under the same conditions as in anion-exchange membrane fuel cells. Electrochemical measurements of oxygen reduction currents showed that the order of electrode performance was DETA-modified < EDA-modified < K-form Nafion (neutralized Nafion with KOH). We effectively improved the TPB region in catalyst layers by introducing aminated Nafion ionomers and revealed the relationship between the conductivity of OH - ion in the aminated Nafion ionomers and the number of amine functional groups in an amine molecule. © 2010 The Electrochemical Society.