Electrochemical Pumping of DMF Electrolyte Solutions across Membranes

Abstract

Electrolysis of ͑dimethylformamide͒ ͑DMF͒ solutions containing tetraalkylammonium iodide salts and dissolved iodine in a two-compartment cell separated by a Nafion membrane results in transfer of solution volume between the two compartments. The pumping process was reversible and the rate, which ranged from 20 to 50 L/min, was controlled by the cell current. The volume of solution pumped was significantly greater than what is predicted from the apparent molar volumes of the species involved in the electrolysis and from the charge passed. The additional volume is attributed to migration-assisted solvent flow across the membrane separator. Comparison of pumping results for a series of Nafion materials indicated that the solvent flow was related to the number of solvent molecules per ion-exchange site in the membrane. Pumping occurred with and against small external pressures up to 0.1 atm. Analysis of apparent molar ionic volumes indicates that the electrode reaction, I 3 Ϫ ϩ 2e Ϫ ϭ 3I Ϫ , contributes little to the observed volume change. Instead, the pumping is associated almost entirely with the apparent molar ionic volume of tetraalkylammonium ions and migration-assisted flow of DMF.

Development of an electroosmotic pump for high performance actuation

“…One approach that could be used to eliminate gas generation would be to eliminate the use of aqueous solutions by employing the iodide/triiodide redox electrolyte in dimethylformamide described by Norman et al [12]. Future studies would be required to demonstrate that the silica membranes retain their surface charge, and thus their pumping capabilities, in this non-aqueous electrolyte solution.…”

“…More recently, Norman et al [12][13][14] described the development of an electrochemical pumping system using cationselective ionomer (Nafion 117) membranes. An iodide/triiodide redox electrolyte was used, formed by a solution of tetraalkylammonium iodide in dimethylformamide.…”

“…The use of this redox couple allowed operation at significant currents without gas generation since there was no electrolysis. The pump was able to generate pressures as high as 2 MPa [14], although the maximum reported flow rate was less than 1 L/s [12].…”

A Nonmechanical, Membrane-Based Liquid Pressurization System

“…This observation is even more surprising, considering that the membrane absorbs 56% of its dry weight in solvent. 9 That is, solvent constitutes more than one-third of this 180-µm-thick membrane, and yet the membrane still has a high resistance to pressure-driven flow. Finally, for the e-pump to generate pressures of this magnitude, pressure-driven backflow must remain minimal concurrent with ion-driven migration in the opposite direction.…”

“…The factors used in the selection of this electrolyte system have been reported elsewhere. [9][10][11] All chemicals were used without further purification. The initial conditions ensure that no concentration difference is observed between compartments, effectively eliminating direct osmotic flow contributions.…”