Nafion-Coating of the Electrodes Improves the Flow-Stability of the Ag/SiO2/Ag2O Electroosmotic Pump

When a current or a voltage is applied across the ceramic membrane of the nongassing Ag/Ag2O-SiO2-Ag/Ag2O pump, protons produced in the anodic reaction 2Ag(s) + H2O → Ag2O(s) + 2H+ + 2e– are driven to the cathode, where they are consumed by the reaction Ag2O(s) + H2O + 2e– → 2Ag(s) + 2 OH–. The flow of water is induced by momentum transfer from the electric field-driven proton-sheet at the surface of the ceramic membrane. About 104 water molecules flowed per reacted electron. Because dissolved ions decrease the field at the membrane surface, the flow decreases upon increasing the ionic strength. For this reason Ag+ ions introduced through the anodic reaction and by dissolution of Ag2O decrease the flow. Their accumulation is reduced by applying Nafion-films to the electrodes. The 20 μL min–1 flow rate of 6 mm i.d. pumps with Nafion coated electrodes operate daily for 5 min at 1 V for 1 month, for 70 h when the pump is pulsed for 30 s every 30 min, and for 2 h when operating continuously.