Sorption of Carbon Dioxide and Nitrogen on Porous Hyper-Cross-Linked Aromatic Polymers: Effect of Textural Properties, Composition, and Electrostatic Interactions.

Porous hyper-cross-linked aromatic polymers are one of the emerging classes of porous organic polymers with the potential for industrial application. Four different porous polymeric materials have been prepared using different precursors (indole, pyrene, carbazole, and naphthalene), and the composition and textural properties were analyzed. The materials were characterized in detail using different physicochemical techniques like scanning electron microscopy, transmission electron microscopy, nitrogen adsorption at 77 K, Fourier transform infrared spectroscopy, X-ray diffraction, etc. The effect of textural properties and nitrogen species on carbon dioxide and nitrogen adsorption capacities and selectivity was studied and discussed. The carbon dioxide and nitrogen adsorption capacities were measured using a volumetric gas adsorption system. The adsorption data were fitted into different adsorption models, and the ideal absorbed solution theory was used to calculate adsorption selectivity. Among the studied samples, POP-4 shows the highest carbon dioxide and nitrogen adsorption capacities. While POP-1 shows maximum CO2/N2 selectivity of 78.0 at 298 K and 1 bar pressure. It is observed that ultra-micropores, which are present in the prepared materials but not measured during conventional surface area measurement via nitrogen adsorption at 77 K, play a very important role in carbon dioxide adsorption capacity and determining the carbon dioxide selectivity over nitrogen. Surface nitrogen also increases the CO2 selectivity in the dual mode by increasing carbon dioxide adsorption via the acid-base interaction as well as by decreasing nitrogen adsorption due to N-N repulsion.

Fabrication of Alkaline Electrolyzer Using Ni@MWCNT as an Effective Electrocatalyst and Composite Anion Exchange Membrane.

Here, we report the synthesis of nickel nanoparticles thermally encapsulated in multiwalled carbon nanotubes (MWCNTs) and its utility in alkaline water splitting by combining with composite thermoset anion-exchange membrane. Ni@MWCNT displayed both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). It provided 10 mA cm-2 current density at an overpotential of 300 mV for OER and 254 mV for HER on a glassy carbon electrode, respectively. Base-catalyzed N-methly-4-piperidone-formaldehyde-based prepolymer was grafted on to poly(vinyl alcohol) and cross-linked via thermal annealing followed by quaternization using methyl iodide to obtain thermoset anion exchange membrane (NMPi). Composite NMPi membranes were synthesized using additives tetraethyl orthosilicate (TEOS) and zirconium oxychloride. The water splitting performance on the fabricated membrane electrode assembly was tested and compared with commercially available Neosepta membrane. The obtained faradic efficacy of the water splitting was 94.33% for ZrO2-NMPi membrane followed by 80.23%, 77.70%, and 65.10% for SiO2-NMPi, NMPi, and Neosepta membranes, respectively. The best membrane ZrO2-NMPi achieved maximum current density of ∼0.776 A cm-2 in 5 M KOH electrolyte at 80 °C and 2 V applied constant voltage. The excellent alkaline stability of MEA indicates its potential utility in hydrogen generation applications.

Low-Voltage Nongassing Electroosmotic Pump and Infusion Device with Polyoxometalate-Encapsulated Carbon Nanotubes.

A low-voltage nongassing electroosmotic pump was assembled by sandwiching a silica frit between two carbon paper electrodes that were dip-coated with a paste consisting of phosphomolybdic acid/phosphotungstic acid (PMA/PTA)-encapsulated multiwalled carbon nanotubes (MWCNTs) and Nafion. The PMA/PTA encapsulation was a combined effect of their thermomigration and nanocapillary action in MWCNTs. The encapsulated MWCNTs retained desirable redox and charge transfer characteristics of PMA/PTA. The stable voltammogram in 1 M H2SO4 solution exhibited 77% charge retention. A total of three different possible pump configurations, namely, PUMP-I = PMA//SiO2//PMA, PUMP-II = PTA//SiO2//PTA, and PUMP-III = PMA//SiO2//PTA were put together. They are in the sequence of the anode, silica frit, and cathode. All pumps showed a linear dependence on the flow rate with a minimum operating voltage of 1 V, which is well below the thermodynamic potential of water splitting. PUMP-I provided an electroosmotic flux of 43.57 µLmin-1 V-1 cm-2 that matched the requirement of an infusion device like an insulin pump. The device was fabricated and its applicability has been demonstrated by delivering ∼1.8 mL of water at a 10 ± 2 µLmin-1 flow rate at 2 V constant applied voltage over a period of 3 h. Such a wearable device can be programed to deliver model insulin or pain medication drugs for chronic diseases.

Alkaline all iron redox flow battery with a polyethylene/poly(styrene-co-divinylbenzene) interpolymer cation-exchange membrane.

This work describes the suitability of a polyethylene styrene-DVB based interpolymer cation exchange membrane for use in a highly alkaline redox flow battery (RFB) with a [Fe(TEA)OH]2-/[Fe(TEA)OH]- and Fe(CN)6 3-/Fe(CN)6 4- redox couple. The alkaline stability of the membrane for 1440 h was evaluated in 5 N NaOH containing a 200 mM Fe(CN)6 3-/Fe(CN)6 4- redox couple. It was assessed according to the changes in the electrochemical and physicochemical properties. The performance of the membrane was evaluated over 40 charge-discharge cycles at a current density of 5 mA cm-2 current in a designed RFB cell. The obtained average coulombic efficiency (CE) was 92%, energy efficiency (EE) was 75%, voltage efficiency (VE) was 82% and volumetric efficiency was 34%. Under identical experimental conditions, the values of CE, EE, and VE for Nafion®-112 were 99%, 75%, and 76%, respectively. These results indicate the suitability of the polyethylene styrene-DVB based interpolymer cation exchange membrane for use in an alkaline RFB.

A non-gassing electroosmotic pump with sandwich of poly(2-ethyl aniline)-Prussian blue nanocomposite and PVDF membrane.

Low voltage, non-gassing electroosmotic pump (EOP) was assembled with poly(2-ethyl aniline) (EPANI)-Prussian blue nanocomposite electrode and commercially available hydrophilic PVDF membranes. The nanocomposite material combines excellent oxidation/reduction capacity of EPANI with exceptional stability by shuttling of proton between Prussian blue nanoparticles and EPANI redox matrix. The flow rate was highly dependent on the electrode composition but it was linear with applied voltage. The flow rate at 5 V for different nanocomposite, EPANI, EPANI-A, EPANI-B, and EPANI-C were 127.29, 187.41, 148.51, and 95.47 µL/min cm2 , respectively, which increases substantially with increase in the Prussian blue content. The obtained best electro osmotic flux was 43 µL/min/V/cm2 for EPANI-A. It was higher than most of the EOP assembled using polyquinone and polyanthraquinone redox polymers. The assembled EOP remained exceptionally stable until the electrode charge capacity was fully utilized. The best EOP produces a maximum stall pressure of 1.2 kPa at 2 V. These characteristics make it suitable for a variety of microfluidic/device applications.

Graphitic carbon coupled poly(anthraquinone) for proton shuttle flow-in-a-cell application.

Coupled electron and proton transport are an integral part of non-gassing electro-osmotic pumps (EOP). The kinetics of the electrode limits the kinetics of the electron transfer and hence the flow. This is observed in the present study with newly synthesized graphitic carbon covalently coupled to poly(anthraquinone) (PAQ). When EOP with identical electrodes were assembled, proton shuttle maintained the reversible flow, which was linearly dependent on the ks values. A Laviron plot was used to calculate the electron-transfer rate constant ks and transfer coefficient α, and their linear dependency on content of graphitic carbon was observed. The best ks value obtained was 0.67 s-1 for 15PAQ. The sandwich-type flow-in-a-cell showed the best result of ∼40 µL min-1 cm-1 V-1 electro-osmotic flux for 15PAQ. It reveals that a balanced combination of graphitic carbon and PAQ is the prime requirement for high-performance electrode materials to be used in microfluidic devices and energy 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.

Mixed-valence metal oxide nanoparticles as electrochemical half-cells: substituting the Ag/AgCl of reference electrodes by CeO(2-x) nanoparticles.

Cations of mixed valence at surfaces of metal oxide nanoparticles constitute electrochemical half-cells, with potentials intermediate between those of the dissolved cations and those in the solid. When only cations at surfaces of the particles are electrochemically active, the ratio of electrochemically active/all cations is ~0.1 for 15 nm diameter CeO(2-x) particles. CeO(2-x) nanoparticle-loaded hydrogel films on printed carbon and on sputtered gold constitute reference electrodes having a redox potential similar to that of Ag/AgCl in physiological (0.14 M) saline solutions. In vitro the characteristics of potentially subcutaneously implantable glucose monitoring sensors made with CeO(2-x) nanoparticle reference electrodes are undistinguishable from those of sensors made with Ag/AgCl reference electrodes. Cerium is 900 times more abundant than silver, and commercially produced CeO(2-x) nanoparticle solutions are available at prices well below those of the Ag/AgCl pastes used in the annual manufacture of ~10(9) reference electrodes of glucose monitoring strips for diabetes management.