Rajaram K. Nagarale

Phosphonic acid functionalized aminopropyl triethoxysilane–PVA composite material: organic–inorganic hybrid proton-exchange membranes in aqueous media

Poly(vinyl alcohol)–silica composite proton-exchange membranes were prepared by a sol–gel process in acidic conditions using aminopropyltriethoxysilane as an inorganic precursor and functionalized with phosphonic acid. Phosphorylation of the membranes was confirmed by Fourier transform infrared (FTIR) spectroscopy and ion-exchange capacity (IEC) studies. These membranes were extensively characterized for their thermal and mechanical stabilities, physicochemical and electrochemical properties using thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), water uptake studies, proton conductivity and methanol permeability measurements. The silica content in the membrane matrix and the time allowed for the phosphorylation were optimized as functions of the membrane properties. It was observed that the PVA–silica composite acts as an excellent methanol barrier possessing good hydrophilicity and proton conductivity. Moreover, from estimation of the selectivity parameter among all the synthesized membranes, 50% silica composition and 3 h of phosphorylation resulted in the best proton-exchange membrane, which exhibited about 20% more suitability in comparison to Nafion 117 membrane for direct methanol fuel cell applications.

Nongassing long-lasting electro-osmotic pump with polyaniline-wrapped aminated graphene electrodes.

An efficient nongassing electro-osmotic pump (EOP) with long-lasting electrodes and exceptionally stable operation is developed by using novel flow-through polyaniline (PANI)-wrapped aminated graphene (NH2-G) electrodes. The NH2-G/PANI electrode combines the excellent oxidation/reduction capacity of PANI with the exceptional conductivity and inertness of NH2-G. The flow rate varies linearly with voltage but is highly dependent on the electrode composition. The flow rates at a potential of 5 V for pristine NH2-G and PANI electrodes are 71 and 100 μL min(-1) cm(-2), respectively, which increase substantially by the use of NH2-G/PANI electrode. It increased from 125 to 182 μL min(-1) cm(-2) as the fraction of aniline increased from 66.63 to 90.90%. The maximum flux obtained is 40 μL min(-1) V(-1) cm(-2) with NH2-G/PANI-90.9 electrodes. The assembled EOP remained exceptionally stable until the electrode columbic capacity was fully utilized. The prototype shown here delivered 8.0 μL/min at a constant applied voltage of 2 V for over 7 h of continuous operation. The best EOP produces a maximum stall pressure of 3.5 kPa at 3 V. These characteristics make it suitable for a variety of microfluidic/device applications.

Low voltage non-gassing electro-osmotic pump with zeta potential tuned aluminosilicate frits and organic dye electrodes

A novel low-voltage non-gassing electro-osmotic pump using organic-dye electrodes and aluminosilicate frits is demonstrated. Good control of the flow rate is achieved by tuning the zeta potential of the frits in the range of −32.7 mV to −52 mV by varying the aluminum concentration of the aluminosilicate microparticles. The flow rate delivered by the pump is linearly dependent on the zeta potential. The aluminosilicate frits with a maximum zeta potential of −52 mV engendered a maximum flow rate of 27 ± 1.5 μL min−1 V−1 cm−2. In a continuous operation lasting 11 h, the assembled electro-osmotic pump (EOP) can deliver 7.3 mL of a test solution at 60 μA current density. The flow resulted from concerted shifting of protons generated at the anode by electro-oxidation. The consumption of protons at the cathode was accompanied by decomposition of the dye. The non-gassing pump was operated at 0.5 V, which is well below the thermodynamic potential of water electrolysis. The obtained flow rate and pumped volume is sufficient to deliver a bolus of insulin for diabetes management.