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Organic-inorganic hybrid membranes based on poly(vinyl alcohol)-SiO2 were prepared under acidic and basic conditions, in which sulfonic acid groups were introduced at the inorganic segment. These membranes were extensively characterized for their morphology, intermolecular interactions, thermal and mechanical stability, and physicochemical properties using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and water uptake studies. Schematic models for acid-catalyzed linear weakly polymeric clusters and for basecatalyzed highly branched polymeric clusters were proposed. A higher ion-exchange capacity, permselectivity, and conductivity for the acid-catalyzed hybrid membranes than for the base-catalyzed membranes with the same composition indicated that the former route is suitable for the preparation of ion-exchange membranes. The electrochemical properties of the membrane and the equivalent pore radius were found to be highly dependent on Si content in the membrane phase. It was concluded that a definite compromise between the silica content and the membrane ion-exchange properties is required in order to have an organic-inorganic hybrid cation-exchange membrane. Furthermore, the physicochemical and electrochemical properties of these membranes were comparable to those of Nafion membrane, which suggests that they may be suitable for fuel cell and chlor-alkali applications as a substitute for Nafion membrane.

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Electroosmotic pumps are arguably the simplest of all pumps, consisting merely of two flow-through electrodes separated by a porous membrane. Most use platinum electrodes and operate at high voltages, electrolyzing water. Because evolved gas bubbles adhere and block parts of the electrodes and the membrane, steady pumping rates are difficult to sustain. Here we show that when the platinum electrodes are replaced by consumed Ag/Ag(2)O electrodes, the pumps operate well below 1.23 V, the thermodynamic threshold for electrolysis of water at 25 °C, where neither H(2) nor O(2) is produced. The pumping of water is efficient: 13 000 water molecules are pumped per reacted electron and 4.8 mL of water are pumped per joule at a flow rate of 0.13 mL min(-1) V(-1) cm(-2), and a flow rate per unit of power is 290 mL min(-1) W(-1). The water is driven by protons produced in the anode reaction 2Ag(s) + H(2)O → Ag(2)O(s) + 2H(+) + 2e(-), traveling through the porous membrane, consumed by hydroxide ions generated in the cathode reaction Ag(2)O(s) + 2 H(2)O + 2e(-) → 2Ag(s) + 2 OH(-). A pump of 2 mm thickness and 0.3 cm(2) cross-sectional area produces flow of 5-30 μL min(-1) when operating at 0.2-0.8 V and 0.04-0.2 mA. Its flow rate can be either voltage or current controlled. The flow rate suffices for the delivery of drugs, such as a meal-associated boli of insulin.