Perfluorinated sulfonyl-fluoride cation-exchange flat-sheet membranes were treated with ethylene diamine to investigate the influence of EDA-surface-treatment on the process of electrochemical "switching" in such membranes. The galvanodynamic method was used to obtain i-V cyclic curves of the membranes. Electroless chemical deposition of Pt particles on modified membranes was achieved using the Takenaka-Torikai method. Galvanodynamic i-V cyclic curves of the plain and platinum-containing aminated membranes were compared. Chemical modification of the membrane surface and membrane structure was investigated by means of electrical conductivity measurements and IR-spectroscopy. Experimental results indicated that the "switching" phenomenon is more likely to occur due to a pH change in the electrolyte resulting in the formation of additional fixed-charged groups in the aminated layers of the membranes rather than due to heterolytic dissociation of water according to the second Wien effect.