Pore-filling Method Research Articles

Development of durable anion-exchange membranes using polyfluorene–based electrolytes and pore-filling method for direct formate fuel cells

Highly durable ether-linkage-free polyfluorene–based electrolytes with different ion exchange capacities (IECs) were synthesized, followed by the preparation and evaluation of cast and pore-filling (PF) membranes as anion exchange membranes (AEMs). The performance of these membranes was tested in direct formate fuel cells (DFFCs). The membrane properties, including formate permeability, were investigated to clarify the relationship between membrane performance and the performance of DFFCs. The formate permeability of the membrane was drastically affected by the existence of OH− anion, as OH− ions induce larger membrane swelling. In addition, the PF method was more effective in reducing the formate permeation than the cast membranes. The PF membrane using the polyelectrolyte with a low IEC value showed 20-fold lower formate permeability compared to that of the original cast membrane, leading to a higher improvement in open-circuit voltage (OCV), from 0.55 to 0.95 V in DFFCs. For the first time, a quantitative correlation between the formate permeability of AEMs and OCV values in DFFCs was established. From this correlation, formate permeation less than 0.03 mol L−1 h−1 is necessary to keep high OCV value. Using the developed membrane, we also demonstrated the high stability of DFFC at 80 °C for 5 days.

Imidazolium-Based Anion Exchange Membranes for Electrochemically Converted Liquid Organic Hydrogen Carrier

Liquid organic hydrogen carrier (LOHC) is a technology that uses renewable energy for hydrogen transportation, storage and utilization. LOHC have advantages that can store and utilize hydrogen rapidly in the lack of transportation infrastructure. A membrane-based LOHC system is a promising technology due to the dynamic operation using electrochemistry. Anion exchange membranes are widely used as electrolyte for electrochemical devices. The performance of LOHC could be determined by the properties of anion exchange membranes. Thus, high anion conducting ionomers must be developed for the superior conversion rates on the electrochemical reduction of liquid toluene to methylcyclohexane. In this study, anion exchangeable polymers containing imidazolium salt as anion-conducting group were synthesized to achieve good conduction of hydroxide ions and their chemical stability. Anion exchange membranes were prepared by a pore-filling method using porous polyethylene substrate. The pore-filling anion exchange membranes were characterized in terms of ion conductivity, areal resistance, ion exchange capacity, water uptake, swelling ratio and mechanical strength. Acknowledgment This research was supported in part by the Korea Institute of Science and Technology (No. 2E31871) and by 2021 Green Convergence Professional Manpower Training Program of the Korea Environmental Industry and Technology Institute funded by the Ministry of Environment.

Bipolar Membranes Containing Iron-Based Catalysts for Efficient Water-Splitting Electrodialysis.

Water-splitting electrodialysis (WSED) process using bipolar membranes (BPMs) is attracting attention as an eco-friendly and efficient electro-membrane process that can produce acids and bases from salt solutions. BPMs are a key component of the WSED process and should satisfy the requirements of high water-splitting capability, physicochemical stability, low membrane cost, etc. The water-splitting performance of BPMs can be determined by the catalytic materials introduced at the bipolar junction. Therefore, in this study, several kinds of iron metal compounds (i.e., Fe(OH)3, Fe(OH)3@Fe3O4, Fe(OH)2EDTA, and Fe3O4@ZIF-8) were prepared and the catalytic activities for water-splitting reactions in BPMs were systematically analyzed. In addition, the pore-filling method was applied to fabricate low-cost/high-performance BPMs, and the 50 μm-thick BPMs prepared on the basis of PE porous support showed several times superior toughness compared to Fumatech FBM membrane. Through various electrochemical analyses, it was proven that Fe(OH)2EDTA has the highest catalytic activity for water-splitting reactions and the best physical and electrochemical stabilities among the considered metal compounds. This is the result of stable complex formation between Fe and EDTA ligand, increase in hydrophilicity, and catalytic water-splitting reactions by weak acid and base groups included in EDTA as well as iron hydroxide. It was also confirmed that the hydrophilicity of the catalyst materials introduced to the bipolar junction plays a critical role in the water-splitting reactions of BPM.

Anion exchange composite membranes composed of poly(phenylene oxide) containing quaternary ammonium and polyethylene support for alkaline anion exchange membrane fuel cell applications

Novel anion exchange composite membranes with controlled thicknesses have been developed by a simple pore-filling method using poly(phenylene oxide) containing a quaternary ammonium group as an anion conducting polymer electrolyte and a polyethylene porous substrate support for alkaline anion exchange membrane fuel cell applications. The thickness optimization could be done by controlling the viscosity of the polymer electrolyte solution. The resulting composite membrane prepared using 5 centipoise (cP) viscous polymer electrolyte solution composed of the co-solvent system such as dimethylacetamide (DMAc) and ethanol showed a uniformly thin structure of about 40 μm thickness. Among the composite membranes developed here, the membrane with the optimized thickness exhibited high tensile strength (45.6 MPa), and a low contact angle (13.19°) indicative of a hydrophilic surface, as well as high hydroxide conductivity (38.9 mS/cm) due to the combined effect of the reinforcement of the robust PE substrate and the sound impregnation of aminated poly(phenylene oxide). Membrane electrode assembly using A-PPO30E200 revealed excellent cell performance (peak power density:153 mW/cm2 at 0.43 V) than those of commercial FAA-3-50 Fumatech anion exchange membrane (peak power density:114 mW/cm2 at 0.43 V) under the operating condition of 60 °C and 100% RH.

Design of Robust Thermal and Anion Dual-Responsive Membranes with Switchable Response Temperature

In this study, poly(ionic liquids/ N-isopropylacrylamide) (PIL/NIPAM) modified poly(ether sulfone) microporous membranes were prepared using a pore-filling method. Due to the anion-sensitive wettability of the PIL and the thermal-sensitive phase transformation of PNIPAM, the permeability of the modified membranes showed robust anion and thermal dual-responsive behaviors. In addition, the response temperature of the membranes could be adjusted precisely from 30 to 55 °C by anion exchange, which was attributed to the cooperative interaction of the PIL and PNIPAM. The switchable response temperature and the dual-responsive performances of the membranes were demonstrated by measuring the water fluxes under various conditions. The results indicated that the membrane permeabilities increased when exchanging the counteranions (CAs) from hydrophilic to hydrophobic ones; the thermal response behaviors were also obvious, and the sensitivity increased when increasing the hydrophobicity of the CA (the fluxes could be adjusted from 0 to 3800 mL/m2 mmHgh by controlling the temperature and CAs). At last, filtration tests were designed with the membranes, and the results indicated that by controlling the temperature and/or CA species, three different poly(ethylene glycol) molecules could be easily separated according to their molecule sizes in a single step.

Fabrication of an Anion-Exchange Membrane by Pore-Filling Using Catechol-1,4-Diazabicyclo-[2,2,2]octane Coating and Its Application to Reverse Electrodialysis.

We have successfully exploited the Michael-type addition reaction between catechol and DABCO (1,4-diazabicyclo-[2,2,2]octane) molecules under alkaline conditions for the formation of new quaternary ammonium (QA) groups in an anion-exchange membrane. The anion-exchange membranes (AEMs) were prepared using the pore-filling method by addition of electrolytes (vinyl benzyl trimethylammonium chloride (VBTMA), dopamine methacrylamide (DMA) bearing a catechol group, and ethylene glycol diacrylate as a cross-linker) to a porous substrate. The formation of new QA groups by the reaction of DABCO with catechol components was confirmed by characterization of new peaks in the Fourier transform infrared spectra of the AEMs. The DABCO-bound AEM demonstrated a significant decrease in area resistance (0.4 Ω·cm2) and increase in permselectivity (94%). Furthermore, the electrochemical properties of the AEMs could be controlled by altering the concentrations of VBTMA and DMA and the formation of new bonds between DMA and DABCO. The calculated theoretical (4.31 W/m2) and practical (1.52 W/m2) power densities during a reverse electrodialysis (RED) process employing the membrane with the best properties (E2C1-DMA0.5-DABCO) were by 33 and 18% higher than those of a system utilizing a commercial membrane, Neosepta AMX (3.25 and 1.29 W/m2). Therefore, the AEM synthesized in this study is a good candidate for use in RED applications.

Luminescent PEO Coatings on Aluminum

Results show the possibilities of pore filling approach to modify alumina coatings with various materials in order to enhance coating optical (or other) properties and develop new functional materials; as well as demonstrate novel alumina phase transition detection approach. Luminescent PEO coatings were produced on aluminum surface using pore-filling method. Three stage process was developed to modify alumina coating in order to enhance its luminescent properties. Eu3+ recharging to Eu2+ followed by significant (up to 10 times) total luminescence intensity increase was observed, Eu ion presence evaluated in final coating by measuring fast decay kinetics. Structure of obtained coatings was analyzed using XRD and FTIR spectroscopy indicating presence of η-alumina phase.

A facile method for the preparation of poly(vinylidene fluoride) membranes filled with cross-linked sulfonated polystyrene

Pores of poly(vinylidene fluoride) (PVDF) membranes were filled with tetrabutylammonium 4-vinylbenzene sulfonate (TVS), a cross-linking agent, and a radical initiator in dimethyl sulfoxide, followed by radical polymerization and subsequent replacement of tetrabutylammonium ions by protons. This pore-filling method using an organic-soluble sulfonate monomer was very efficient and convenient, as it avoids the highly acidic sulfonation step. The dimensional changes in the length of the PVDF membranes filled with cross-linked sulfonated polystyrene were similar to Nafion 212, but their water uptakes were higher and they exhibited greatly improved mechanical moduli and elongations. Proton conductivities of the modified membranes were also higher than Nafion 212 under identical conditions.

Polytetrafluoroethylene (PTFE)/silane cross-linked sulfonated poly(styrene–ethylene/butylene–styrene) (sSEBS) composite membrane for direct alcohol and formic acid fuel cells

A novel polymeric electrolyte membrane for direct alcohol fuel cells (DAFCs) and direct formic acid fuel cells (DFAFCs) was developed using a pore-filling method. This composite consisted of a porous polytetrafluoroethylene (PTFE) microporous substrate filled with silane-crosslinked sulfonated poly(styrene–ethylene/butylene–styrene) (sSEBS). This composite membrane was characterized using field emission scanning electron microscopy, Fourier-transform infrared spectrometry, thermal gravimetric analysis, and differential scanning calorimetry. The thermal and mechanical stabilities of this composite membrane were good. The methanol and ethanol permeabilities of this composite membrane were lower than Nafion 117, and these two membranes had comparable ionic conductivities. The power densities in direct methanol fuel cells with this composite electrolyte were higher than with the Nafion electrolyte. A peak power density of 91.4mWcm−2 was achieved at 70°C when the cell was fed with 0.5M methanol. A direct ethanol fuel cell using this composite exhibited a peak power density of 16.5mWcm−2 at 60°C. In a DFAFC, a peak power density of 81.4mWcm−2 was achieved with this composite and 3M fuel at 60°C. Long-term cell performance was sustained during a 180-h continuous operation using this pore-filled PTFE/sSEBS composite electrolyte. This PTFE/sSEBS composite membrane has potential for use in proton-exchange DAFC and DFAFC applications.

Development of bench and full-scale temperature and pH responsive functionalized PVDF membranes with tunable properties

Temperature and pH responsive polymers (poly(N-isopropylacrylamide) (PNIPAAm), and polyacrylic acid, PAA) were synthesized in one common macrofiltration PVDF membrane platform by pore-filling method. The microstructure and morphology of the PNIPAAm–PVDF, and PNIPAAm–FPAA–PVDF membranes were studied by attenuated total reflectance Fourier transform infrared (ATR-FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The membrane pore size was controlled by the swelling and shrinking of the PNIPAAm at the temperature around lower critical solution temperature (LCST). The composite membrane demonstrated a rapid and reversible swelling and deswelling change within a small temperature range. The controllable flux makes it possible to utilize this temperature responsive membrane as a valve to regulate filtration properties by temperature change. Dextran solution (Mw=2,000,000g/mol, 26nm diameter) was used to evaluate the separation performance of the temperature responsive membranes. The ranges of dextran rejection are from 4% to 95% depending on the temperature, monomer amount and pressure. The full-scale membrane was also developed to confirm the feasibility of our bench-scale experimental results. The full-scale membrane also exhibited both temperature and pH responsivity. This system was also used for controlled nanoparticles synthesis and for dechlorination reaction.

A reversible water electrolyser with porous PTFE based OH− conductive membrane as energy storage cells

An OH− conductive anion exchange membrane was prepared by a pore-filling method with porous polytetrafluoroethylene and a quaternary ammonium polymethacrylate ionomer. The composite membrane exhibited less swelling ratios of thickness and area variation and stronger tensile strength than the pristine polymethacrylate membrane. The ionic conductivity of the composite membrane was not as good as the pristine polymethacrylate ionomer membrane. However, the composite membrane was ultra-thin therefore it leaded to a smaller ionic resistance of the MEA and improved current densities. In fuel cell mode, the peak power densities were respectively 0.114 and 0.163 W cm−2 at 20 and 45 °C. In water electrolyser mode, at a current density of 100 mA cm−2 the cell voltages were about 1.61 V and 1.52 V respectively at 22 °C and 50 °C. In the water electrolyser mode, the degradation rate was only 0.0379 mV h−1 after 120 h at a current density of 100 mA cm−2 at 22 °C.

Fe-based catalysts for oxygen reduction in proton exchange membrane fuel cells with cyanamide as nitrogen precursor and/or pore-filler

Fe/N/C catalysts for oxygen reduction reaction were synthesized via impregnation or ballmilling. The role of cyanamide (CM) as nitrogen precursor and/or pore-filler for a highly microporous carbon (Black Pearls 2000) was investigated. The use of CM in this work resulted in two main differences compared with phenanthroline from our previous work; (i) ballmilling the precursors did not result in improved activity of the resulting catalysts, and (ii) the activity after the first pyrolysis in argon was relatively high, but did not increase after a second pyrolysis in NH 3. These differences may be explained by TGA measurements of both pore-fillers, where complete gasification of CM is observed at temperatures above 750 °C in Ar, while pyrolysis of phenanthroline in Ar results in 20 wt% residual carbon-based material. Consequently, when using CM as pore-filler with a highly microporous carbon support, the maximum microporous surface area and nitrogen content is reached after only a single pyrolysis in Ar. The most active catalyst prepared with CM was obtained by pyrolysing in Ar at 950 °C a catalyst precursor containing 1 wt% Fe, 80 wt% CM and Black Pearls 2000. This catalyst possessed about 1/6th the catalytic activity of best reported using phenanthroline as a pore-filler. Changing the carbon support had effects on the activity and stability of the catalysts. The catalysts made with a non-porous furnace black (N330) or carbon nanotubes as a carbon support were more stable but less performing than those using carbon supports having high microporous surface area like Black Pearls 2000 or Ketjenblack. The desirable properties for a pore-filler molecule used in the synthesis of Fe/N/C-catalysts by the pore-filling method are discussed.

Solid Dispersions of Carvedilol with Porous Silica

Solid dispersion particles of carvedilol (CAR) were prepared with porous silica (Sylysia 350) by the solvent evaporation method in a vacuum evaporator to ensure an effective pore-filling procedure. Two sets were prepared, each with various amounts of CAR in solid dispersions, and with the pore-filling process differing each time. Set A was prepared by a one-step filling method and set B by a multiple-step pore-filling method of CAR into porous silica. The solid dispersions were then characterized using thermal analysis, X-ray diffraction, and nitrogen adsorption experiments. The results showed that the drug release can be significantly improved compared with the dissolution of the drug in its pure crystalline or amorphous state. Drug release from solid dispersion was faster when the drug content in the solid dispersion was low, which enabled the drug to be finely dispersed along the hydrophilic carrier's surface. The results also showed that a multiple-step pore-filling procedure is more effective for drug loading as indicated by the absence of a crystalline drug state, greatly reduced porosity, and improved wettability and physical stability of the amorphous CAR.

Mesoporous Si-MCM-48 membrane prepared by pore-filling method

Mesoporous MCM-48 membranes were prepared on asymmetric zirconia tubular support with an average pore size of 0.2 μm by hydrothermal method. The support should be pretreated with H2O as a pore-filling substance to prevent the sol solution from infiltrating into the support pores. The SEM showed that the MCM-48 membrane was composed of tightly-connected spherical crystal. The single gas N2 and H2 permeation experiments confirm that crack-free membrane could be prepared by pore-filling method. N2 permeance of MCM-48 membrane, synthesized by secondary growth, can reach 5.66×10−7 mol/Pa·s·m2, and the H2/N2 separation factor was 3.47 under trans-membrane pressure of 0.05 MPa.

Iron-based Catalysts for Oxygen Reduction in PEM Fuel Cells: Expanded Study Using the Pore-filling Method

Fe/N/C catalysts for the oxygen reduction reaction (ORR) in PEM fuel cells were synthesized via a new method. A catalyst precursor was first prepared by filling the pores of a microporous carbon black with a mixture of pore-filler (organic molecules) and iron precursor by means of planetary ballmilling. The resulting catalyst precursor was then pyrolysed either in NH3 only or, first in Ar and then in NH3. Various pore-fillers and carbon blacks were investigated. The ORR activity in fuel cell is influenced by (i) the type and mass ratio of the pore-filler and the nominal loading of iron in the catalyst precursor and (ii): the micropore surface area and nitrogen content in the catalyst. The highest kinetic activity obtained in fuel cell at 0.8 V iR-free is 429 A g-1 using 1 wt% nominal iron loading, phenanthroline as the pore-filler and Black Pearls 2000 as the microporous carbon black

Increased nanopore filling: Effect on monolithic all-solid-state dye-sensitized solar cells

A vacuum pore-filling method is described to fabricate solid-state dye-sensitized solar cells (DSSCs) based on nanocomposite polymer electrolytes. Scanning electron microscopy and energy dispersive x-ray spectrometry analyses suggest that incomplete pore filling of the nanostructured TiO2 electrodes is a major efficiency-limiting factor in the fabrication process of solid-state DSSC. Application of the vacuum method resulted in DSSC with much improved energy conversion efficiencies when compared to devices made via conventional drop-casting technique. The energy conversion efficiency gain increased steadily with increasing TiO2 film thicknesses. It is expected that the vacuum pore-filling technique will be applicable to a wide range of hole-transport materials.

Anodic alumina films formed in sulfamic acid solution

The formation of anodic oxide films on aluminium in 5% aqueous solution of sulfamic acid is investigated. The investigations were carried out in galvanostatic conditions and at different temperatures and durations. The porosity of porous alumina samples grown under different conditions is determined by the pore-filling method and scanning electron microscopy. The effect of the current density, temperature and duration of the anodic oxidation on the morphology of the porous Al2O3-films is studied.

The influence of the anodization temperature and voltage on the porosity of the anodization layer on aluminium

The pore-filling method is a known process for measuring the porosity of porous anodic oxide layers on aluminium. This method has been used to study the relationship between the anodizing conditions and the porosity of the porous anodic film. In a series of experiments, the influence of the anodization voltage and temperature on the porosity, of an anodization layer formed in 15 wt.% sulphuric acid was investigated. From these results a mathematical equation was deduced that gives the porosity as a function of the anodization voltage and temperature. In the second part of the study the height of the voltage jump, on which the thickness of the barrier layer at the start of the re-anodization process depends, was investigated as a function of the anodization voltage. A linear relationship was found between the voltage jump and the anodization voltage.

Nickel-based heterogeneous catalysts for olefin oligomerization: I. Support and anion effects

Using the pore-filling method, a series of catalysts were prepared by impregnation of various inorganic oxides (silica, alumina and silica-alumina) with aqueous solutions of nickel nitrate, sulphate or chloride. Calcination in air at 5OO°C completely decomposed the nitrate ions and partially removed the chloride ions, whereas the sulphate ions remained entirely in the catalysts. The catalysts thus pretreated were tested in the liquid-phase oligomerization of propene at 40°C and a pressure of 0.4 MPa. The catalysts derived from nickel nitrate deposited on silica or alumina exhibited no activity, whereas all the others were active. The NiCl 2/Al 2O 3 catalyst turned out to be the most active and selective. The influence of the nature and the amount of associated ions (sulphate, chloride) on the activity and selectivity for propene oligomerization was investigated and their role is discussed in terms of support acidity.

Surface and catalytic properties of gamma-irradiated CuO/Al 2O 3 solids

Copper/aluminum mixed oxide solid, having the composition 0.25 CuO:Al 2O 3, was prepared by impregnating Al(OH) 3 with cupric nitrate using a pore-filling method, followed by heating in air at 300°C. The obtained solid was exposed to different doses of γ-irradiation, viz. 20, 40, 80, 120 and 160 Mrad. The surface area ( S BET), the total pore volume ( V p) and mean pore radius ( r ) of various treated solids were investigated by N 2 adsorption at 77 K. The catalytic oxidation of CO by O 2 on different irradiated catalysts was carried out at 95–145°C and a total pressure of 2 torr using a static technique. The results obtained revealed that γ-irradiation effected a decrease of 15–40% in the S BET and a decrease of 18–33% in the V' p of the treated solids. The doses up to 120 Mrad induced no important effect in the value of r which was found to increase (76%) by the exposure to a dose of 160 Mrad. In contrast, the irradiation process effected a considerable increase of 250–500% in the catalytic activity of the treated catalysts, depending on the dose employed and the temperature of the catalytic reaction. The activation energy of the catalytic reaction remained almost unchanged (9 ± 1 kcal/mol -1), indicating that the catalytic reaction took place via the same mechanism over different irradiated catalysts. These results were attributed to an increase in the concentration of the catalytically active sites, Cu 2+ cations, via desorption of strongly-bound chemisorbed oxygen and removal of OH groups from the outermost surface layers of the catalyst by absorption of γ-ray dose.