AC-IMPEDANCE INVESTIGATIONS OF PROTON CONDUCTION IN NAFION(TM)

AC impedance spectroscopy has been employed to study the conduction of protons in Nation 117 polymer electrolyte membranes. Both two- and fo ur-electrode geometries have been used to uniquely distinguish between the membrane impedance and the interfacial impedances. The results sh ow that the impedance of Nation for frequencies up to 100 kHz is chara cterized by a pure resistance, similar to conventional liquid electrol ytes. The frequency dependent features observed using a two-electrode geometry are shown to be consistent with well-characterized interfacia l impedances and do not arise from ionic conduction in the membrane. T hese results show that previous two-electrode studies reported in the literature have misinterpreted the impedance of the electrode interfac es as belonging to the conduction process in the electrolyte.