(29c) Electrochemical Impedance Spectroscopic Studies of Non-Fluorinate Proton Exchange Membranes in Dmfc

In direct methanol fuel cell (DMFC), protons and carbon dioxide are catalytically produced at the anode. The protons migrate through the membrane and react catalytically with oxygen to produce water at the cathode. Methanol transported across the membrane can react at the cathode without producing electricity. This not only lowers fuel utilization, but also adversely effects cathode performance. A successful DMFC membrane must not only conduct protons, but also prevent methanol transport.

This work explores the potential of novel membranes in DMFC. Hybrid membranes of inorganic and organic materials are developed in our studies. The membranes have demonstrated characteristics that suggest about 10-fold improvement in DMFC. This improvement may be due to an alternate form of proton conduction in which protons travel via a Grotthus or ``hopping'' mechanism. The characteristics of a membrane and its effects on the performance of fuel cell are investigated by means of electrochemical impedance spectroscopy (EIS). The EIS results have shown that ohm resistance, charge transfer resistance and mass transport resistance increase with discharging time. At high current densities, the water content on the anode side of the electrolyte increases due to electro-osmotic drag. As a consequence, the performance loss is probably due to water shortage at the outlet of cathode obstructing our passive DMFC to breathe air.

Key words: direct methanol fuel cell, electrochemical impedance spectroscopy, membrane electrode assembly