Study of the electromotive force of electrochemical cell with polymeric membrane oriented in horizontal plane.

In order to characterize processes proceeded in concentration boundary layers (CBLs), divided by neutral and horizontally mounted membrane, the electromotive force (EMF) during and after turning off mechanical stirring of aqueous KCl solutions was measured. The EMF was measured by means of Ag / AgCl electrodes and electrometer connected with a microcomputer. Aqueous solutions of KCl with fixed and lower concentration Cl = 10(-5) mol x l(-1) was over the membrane, while KCl concentration under the membrane Ch > Cl was changed. Such configuration of membrane system caused stable reconstruction of CBLs after turning off mechanical stirring of solutions in electrochemical cell. On the basis of time dependencies of EMF the concentration dependencies were performed and it was stated that dependencies of EMF = f(Ch/Cl) are nonlinear. It was found that maximal value of EMF, equal to 175 mV, was observed during mechanical stirring of solutions for Ch/Cl = 400. In order to interpret experimental results, the model of EMF changes in time after turning off mechanical stirring was elaborated on the basis of Kedem-Katchalsky model equations for transport of electrolytes through the membrane. The transport number of K+ ions (t+), appointed for the membrane, depended nonlinearly on Ch/Cl and for Ch/Cl = 50 was maximal and amounted to t(+max) = 0.7. Besides, concentration dependence of relaxation time of CBLs reconstruction after turning off mechanical stirring was appointed. For Ch/Cl < 500, increase of Ch/Cl caused considerable decrease of relaxation time, while for Ch/Cl > 500 the relaxation time was small and did not change considerably with increase of Ch/Cl, in this range.