Proton Conducting Organic-Inorganic Composite Membranes for All-Vanadium Redox Flow Battery.

The quest for a cost-effective, chemically-inert, robust and proton conducting membrane for flow batteries is at its paramount. Perfluorinated membranes suffer severe electrolyte diffusion, whereas conductivity and dimensional stability in engineered thermoplastics depend on the degree of functionalization. Herein, we report surface-modified thermally crosslinked polyvinyl alcohol-silica (PVA-SiO2) membranes for the vanadium redox flow battery (VRFB). Hygroscopic, proton-storing metal oxides such as SiO2, ZrO2 and SnO2 were coated on the membranes via the acid-catalyzed sol-gel strategy. The membranes of PVA-SiO2-Si, PVA-SiO2-Zr and PVA-SiO2-Sn demonstrated excellent oxidative stability in 2 M H2SO4 containing 1.5 M VO2+ ions. The metal oxide layer had good influence on conductivity and zeta potential values. The observed trend for conductivity and zeta potential values was PVA-SiO2-Sn > PVA-SiO2-Si > PVA-SiO2-Zr. In VRFB, the membranes showcased higher Coulombic efficiency than Nafion-117 and stable energy efficiencies over 200 cycles at the 100 mA cm-2 current density. The order of average capacity decay per cycle was PVA-SiO2-Zr < PVA-SiO2-Sn < PVA-SiO2-Si < Nafion-117. PVA-SiO2-Sn had the highest power density of 260 mW cm-2, while the self-discharge for PVA-SiO2-Zr was ~3 times higher than Nafion-117. VRFB performance reflects the potential of the facile surface modification technique to design advanced membranes for energy device applications.

Chitosan-cross-linked osmium polymer composites as an efficient platform for electrochemical biosensors.

A new family of chitosan-cross-linked osmium polymer composites was prepared and its electrochemical properties were examined. The composites were prepared by quaternization of the poly(4-vinylpyridine) osmium bipyridyl polymer (PVP-Os) which was then cross-linked with chitosan, yielding PVP-Os/chitosan. Films made of the composites showed improved mass and electron transport owing to the porous and hydrophilic structure which is derived from the cross-links between the Os polymer and chitosan. The rate for glucose oxidation was enhanced four times when glucose oxidase (GOx) was immobilized on PVP-Os/chitosan compared immobilization on PVP-Os.

Hydroquinone modified chitosan/carbon film electrode for the selective detection of ascorbic acid.

A redox active polymer, hydroquinone modified chitosan (Q-chitosan) was synthesized and characterized by IR and (1)H NMR spectroscopy. The nanocomposite of Q-chitosan with carbon was prepared and used to construct a stable conductive film on the electrode surface. The SEM studies confirms that the Q-chitosan/C composite covers the electrode surface with polymer embedded 50 nm size carbon particles. The formal redox potential, E(0) of the Q-chitosan/C composite modified electrode is evaluated to be 0.09 V vs. Ag/AgCl at pH 7 and the composite electrode shows an excellent electrocatalytic activity toward the ascorbic acid (AA) at 0.0 V vs. Ag/AgCl. It is more negative potential than the similar AA biosensors and the lower potential oxidation of AA enabled the selective detection of AA over major interferences such as dopamine and uric acid. Using amperometric method, the linear range for ascorbic acid is estimated to be 10 µM to 5 mM with the detection limit of 3 µM and the sensitivity is 0.07 6µA µM(-1)cm(-2).

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/Ag(2)O-SiO(2)-Ag/Ag(2)O pump, protons produced in the anodic reaction 2Ag(s) + H(2)O → Ag(2)O(s) + 2H(+) + 2e(-) are driven to the cathode, where they are consumed by the reaction Ag(2)O(s) + H(2)O + 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 10(4) 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 Ag(2)O 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.

A miniature, nongassing electroosmotic pump operating at 0.5 V.

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.

A miniature, single use, skin-adhered, low-voltage, electroosmotic pumping-based subcutaneous infusion system.

A programmable, skin-attached, 36 × 30 × 8 mm system for subcutaneous infusion of 1.2 mL of a drug solution is described. The system is intended to be replaced daily. It comprises a 20 × 14 × 8 mm electronic controller and power source, an 8 mm diameter 2 mm thick electroosmotic pump, a two-compartment reservoir for a pumped water and a drug solution, an adhesive tape for attachment to the skin, and a 6 mm long 27 gauge needle. Its removable electronic controller programs the dose rate and dose and is re-used. The electroosmotic pump consists of a porous ceramic membrane sandwiched between a pair of Ag/Ag2O plated carbon paper electrodes. It operates below 1.23 V, the thermodynamic threshold for water electrolysis without gassing. The flow rate can be adjusted between 4 and 30 µL min(-1) by setting either by the voltage (0.2-0.8 V) or the current (30-200 µA). For average flow rates below 4 µL min(-1), the pump is turned on and off intermittently. For example, a flow rate of 160 µL day(-1), i.e., 0.13 µL min(-1) for basal insulin infusion in type 1 diabetes management, is obtained when 10 s pulses of 75 µA is applied every 15 min. High flow rates of 10-30 µL min(-1), required for prandial insulin administration, are obtained when the pump operates at 50-200 µA. To prevent fouling by the drug, only pure water passes the pump; the water pushes a drop of oil, which, in turn, pushes the drug solution.