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We propose an approach to improve the triple phase boundary ͑TPB͒ of catalyst layers in anion-exchange membrane fuel cells by using aminated Nafion ionomers with amine molecules of ethylenediamine ͑EDA͒ and diethylenetriamine ͑DETA͒ 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 − = 0.89͒ was larger than that of the EDA-modified Nafion ͑t − = 0.81͒. Pt/C catalyst layers with EDA-and DETAmodified 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 Ͼ EDA-modified Ͼ K-form Nafion ͑neutralized Nafion with KOH͒. 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. ͓DOI: 10.1149/1.3483105͔ All rights reserved. There is increasing interest in the application of anion-exchange membrane fuel cells ͑AEMFCs͒ as a next-generation electric power source. In contrast with conventional proton exchange membrane fuel cells ͑PEMFCs͒, AEMFCs have some advantages for an electrochemical system in working principles. First, cell reactions in AEMFCs proceed under basic conditions, which lead to faster kinetics of electrode reactions. Second, nonprecious metal catalysts can be accepted to efficiently enhance cell reactions. Nowadays, there has been considerable research about AEMFCs because of the above advantages and the development of various anion-exchange membranes ͑AEMs͒.Both AEMFCs and PEMFCs are in the same type of fuel cells: polymer electrolyte fuel cells ͑PEFCs͒. PEFCs usually include ionconducting membranes such as AEMs and proton exchange membranes, and hydrogen-oxidation and oxygen-reduction reactions occur to generate electric power. In these PEFCs, cell reactions mainly occur at the encounter points of catalysts, ion conductors, and gaseous reactants. These reactive points are called as the triple phase boundary ͑TPB͒ regions. Even if a point lacks one phase, the point becomes inactive for cell reactions. Therefore, the amount and conditions of the TPB play a dominant role on the performance of PEFCs. 1,2In particular, proton-conducting ionomer solutions such as Nafion solution are used to fabricate an appropriate TPB region in catalyst layers in PEMFCs. The method of casting Nafion solution into a porous catalyst layer was invented, 1,3,4 and recently, a catalyst layer was made from a slurry of catalyst powder containing Nafion solution.5 These proton-conducting ionomer solutions drastically increase the performance of PEMFCs. In the same manner as...