An impedance analysis on properties of DMFC catalyst layers based on primary and secondary pores

An impedance analysis method for the catalyst layers of a direct methanol fuel cell is evaluated through demonstrating analyses and comparison of two types of the catalyst layers. The catalyst layers were prepared with different dispersing solvents: ethyleneglycol dimethyl ether or isopropyl alcohol aqueous solution. Methanol oxidation current of the catalyst layer prepared with the former solvent was more than twice that with the latter. The proposed method was revealed to have the potential for analyzing the difference clearly in terms of parameters, using our transmission-line equivalent circuit for the catalyst layers based on the assumption of primary and secondary pores. The parameters indicate that the main drawback of the catalyst layer prepared with the latter solvent is 85 times larger ionic resistance in the secondary pores. Moreover, precise analyses on the parameters indicate the microstructures of the catalyst layers, which correspond to a model reported previously. We conclude that this method is effective in analyzing the catalyst layer of the fuel cell. (C) 2007 The Electrochemical Society.