High Acid Uptake Research Articles

Cross-Linked Polybenzimidazoles Containing Porous Organic Cages for High-Temperature Proton Conduction

We prepared a series of porous organic cages (POCs) with cross-linked polybenzimidazole membranes. Because of the introduction of the POC with numerous amine groups and ultramicroporous structures in the polymers, which enhanced the PA interactions and increased free volume, the POC-PBI membranes exhibited better proton conductivity and higher acid uptake. 20%-POC-OPBI showed the highest conductivity at 47.2 mS cm−1, followed by OPBI at 27.2 mS cm−1.

Poly(N-vinyl triazole-b-N-vinyl imidazole) Grafted on MWCNTs as Nanofillers to Improve Proton Conducting Membranes

Carbon nanotubes (CNTs) are of particular interest because of their ability to enhance the mechanical strength in the material; however, processing difficulties of CNTs often restrict utilization up to its full potential. To resolve this, in the current study, we have developed a simple and efficient method to functionalize the surface of a multiwalled carbon nanotube (MWCNT) with precise functional polymer chains, which were covalently grafted on the surface of the MWCNT, and delved into an application to demonstrate this material as an efficient nanofiller in developing a proton conducting membrane (PEM) from polybenzimidazole (PBI). At first, the MWCNT surface was converted to a polymerizable surface by attaching a trithiocarbonate based chain transfer agent (CTA). Then, a N-heterocyclic block copolymer, namely poly-N-vinyl-1,2,4-triazole-b-poly-N-vinyl imidazole (pNVT-b-pNVI), was grown from the CTA anchored surface with a one-pot surface initiated reversible addition–fragmentation chain transfer (SI-RAFT) technique. Grafting of block copolymer chain was confirmed by GPC, NMR, TGA, TEM, FESEM, and EDX studies. To the best of our knowledge, this will be the first report of a growing block copolymer structure grafted covalently on the surface of the MWCNT. The novelty of the work was further enhanced by incorporating pNVT-b-pNVI-g-MWCNT as a nanofiller into the oxypolybenzimidazole (OPBI) membrane to obtain homogeneous nanocomposite membranes with excellent thermomechanical and tensile properties, thermal stability, superior proton conduction when doped with phosphoric acid (PA), and PA holding capacity. The nanocomposite membrane with 2.5 wt % nanofiller loading displayed a tensile stress of 1.8 MPa and a strain of 176% at break. The basic N-heterocyclic rings dangling from the block copolymer chains grafted on the MWCNT surface allowed formation of strong H-bonding, acid–base interaction with PA, which is responsible for high acid uptake and superior PA retention, and also exhibited proton conductivity as high as 0.164 S cm–1 at 180 °C, which is a 2.6-fold increment when compared with a pristine OPBI membrane. This significant increase in conductivity is attributed to the proton conducting nanochannel pathway generated along the polymer-g-MWCNT surface.

High-temperature PEMs based on polybenzimidazole and new nanoparticles for fuel cell application

The aim of the present work is employing BaCe0.85Yb0.15O3-δ nanoparticles for improving textural properties and performances of proton exchange membranes based on polybenzimodazole (PBI) at high operation temperature. The novel proton conducting membrane nanocomposites are prepared by using various weight percent amounts of BaCe0.85Yb0.15O3-δ nanomaterial by dispersing into polybenzimidazole using solution casting method. The nanocomposites membranes properties are studied using AC impedance spectroscopy, scanning electron microscope (SEM) coupled with energy dispersive X-ray (EDX) spectroscopy and thermo gravimetric analysis (TGA). The prepared nanocomposites membranes reveal higher acid uptake, better protonic conductivity and thermal stability compared to pure PBI membranes. Highest acid uptake and protonic conductivity properties are obtained for phosphoric acid-doped PBI nanocomposites membranes while the inorganic compotent amount in the membrane composite is 5 wt.%. The prepared nanocomposites membranes are used in fuel cell sytems. Polarization property and power curves of the prepared membranes are studied at 180 °C. The results show that the obtained PBI/BaCe0.85Yb0.15O3-δ nanocomposites has excelent potentials as proton exchanger membranes for high temperature fuel cell systems.

Spectroscopic Study of Reinforced Cross-Linked Polymeric Membranes for Fuel Cell Application.

Acid-doped reinforced polymer electrolyte membranes for high-temperature polymer electrolyte membrane fuel cell applications (HT PEMFCs) are presented and spectroscopically studied. Fully aromatic polyethers are employed bearing main chain pyridine units as the proton accepting sites, which have two different substitution patterns of the pyridine units, namely, 2,5- or 2,6-pyridine. This fact enables control of the solubility and of the acid doping ability of the polymeric membranes. Reinforcement is accomplished via incorporation of a PTFE woven fabric during the casting procedure for fabrication of the membranes. High acid uptake of the reinforced membranes was maintained for the 2,6-pyridine-based copolymers with high pyridine unit content. Studies of the swelling behavior of these reinforced membranes revealed that they expand mainly along the z-axis, which helps to avoid extensive damage in case of humidity or temperature changes during the fuel cell operation. Additionally, spectroscopic techniques are employed, namely, X-ray photoelectron spectroscopy, X-ray photoelectron spectroscopy with depth profile, near-edge X-ray absorption fine structure, and reflection electron energy loss spectroscopy, for the in-depth study of the two copolymer membranes doped with phosphoric acid. Through these spectroscopic evaluations, modifications in the membranes’ chemical structure, orientation, composition, and electronic structure after the reinforcement and doping processes were elaborated and unveiled.

Polybenzimidazole-nanocomposite membranes: Enhanced proton conductivity with low content of amine-functionalized nanoparticles

In this work, a pyridine based polybenzimidazole (PPBI) is synthesized (I.V. 3.3 dL/g) from pyridine dicarboxylic acid and hydrochloride salt of diaminobenzidine. The polymer is characterized by FTIR and 13C CP-MAS NMR. The resultant PPBI possesses high storage modulus of >10 GPa, tensile modulus of ∼1 GPa and tensile strength of ∼150 MPa. Amine functionalized silica nanoparticles in different degrees of amine grafting (LAC-low amine content/HAC-high amine content) are successfully incorporated into PPBI to result nanocomposite membranes. Both the neat PPBI and nanocomposites exhibit significant affinity towards phosphoric acid as indicated by the high acid uptake in short time (5 h). Proton conductivity of nanocomposites is increased by the addition of LAC/HAC nanoparticles (>250 mS/cm at 140 °C). The HAC nanoparticle enriched nanocomposite (HAC 7) reveals self-assembly of amino-silica nanoparticles due to base-base repulsion (imidazole-amine). Hydrophobicity of nanocomposite membranes is increased with increase in LAC/HAC content which is attributed to the strengthening of hydrogen bonding between PPBI and nanoparticles.

(Invited) Crosslinked High Temperature Polymer Electrolyte Membranes

High temperature polymer electrolyte membranes containing basic units that are able to interact with strong protic acids providing ionically conductive composite membrane have shown respectable performance and long operational stability. Further increase of the operation temperature and even an increase on the obtained conductivity values would facilitate the construction of efficient systems providing both electricity and heat, increasing thus the total efficiency. Initial attempts to stabilize the HTPEM electrolyte membranes through covalent crosslinking have proven that the operation temperature can be shifted up to 220oC 1,2. Different crosslinking methodologies have been tested to stabilize either PBI or aromatic polyethers bearing pyridine units3,4. In the present work we focused on the optimization of the crosslinking methodology using side double bonds and we also develop new crosslinking methodologies leading to wholly aromatic crosslinked structures. Different type of crosslinkers have been used, controlling thus the acid doping ability of the final membranes while the use of dopable crosslinkers that enable the high acid uptake and retention. Moreover, depending on the chemical structure of the crosslinked membranes, a significant increase of the conductivity values of the final acid doped composite membranes was obtained. High temperature operation as the one achieved here enables the use of liquid feed like methanol in a compact methanol reformer-high temperature PEM fuel Cell setup that is under construction and testing5.

Amino‐Functional Polybenzimidazole Blends with Enhanced Phosphoric Acid Mediated Proton Conductivity as Fuel Cell Electrolytes

A new amino‐functional polybenzimidazole copolymer is synthesized by homogeneous solution condensation polymerization from a novel monomer, N,N′‐bis(2,4‐diaminophenyl)‐1,3‐diaminopropane. The copolymer readily dissolves in organic solvents and shows good film forming characteristics. To balance the phosphoric acid uptake and to obtain mechanically robust membranes, the amino‐functional polybenzimidazole derivative is blended with high molecular weight poly[2,2′‐(m‐phenylene)‐5,5′‐bisbenzimidazole] at different ratios. Due to the high acid uptake, the homogenous blend membranes show enhanced proton conductivity at temperatures well above 100 °C as also confirmed by the fuel cell polarization data. image

Novel nanocomposite membranes based on polybenzimidazole and Fe2TiO5 nanoparticles for proton exchange membrane fuel cells

In this work, Fe2TiO5 nanoparticles were used for improving the proton conductivity, and water and acid uptake of polybenzimidazole (PBI)-based proton exchange membranes. The nanocomposite membranes have been prepared using different amounts of Fe2TiO5 nanoparticles and dispersed into a PBI membrane with the solution-casting method. The prepared membranes were then physico-chemically and electrochemically characterized for use as electrolytes in high-temperature PEMFCs. The PBI/Fe2TiO5 membranes (PFT) showed a higher acid uptake and proton conductivity compared with the pure PBI membranes. The highest acid uptake (156 %) and proton conductivity (78 mS/cm at 180 °C) were observed for the PBI nanocomposite membranes containing 4 wt% of Fe2TiO5 nanoparticles (PFT4). The PFT4 composite membrane showed 380 mW/cm2 power density and 760 mA/cm2 current density in 0.5 V at 180 °C at dry condition. The above results indicated that the PFT4 nanocomposite membranes could be utilized as proton exchange membranes for high-temperature fuel cells.

Polybenzimidazole/strontium cerate nanocomposites with enhanced proton conductivity for proton exchange membrane fuel cells operating at high temperature

In this work, perovskite-type SrCeO3 nanoparticles were used for improving the properties of high temperature polybenzimodazole (PBI) based proton exchange membranes. Novel proton conducting membrane nanocomposites were prepared using different amounts of SrCeO3 nanopowders dispersed into by solution casting method.The nanocomposite membranes were studied by using AC impedance spectroscopy, scanning electron microscopy coupled with energy dispersive X-ray and thermo gravimetric analysis. The prepared nanocomposite membranes showed a higher acid uptake, proton conductivity and thermal stability compared with the pure PBI membranes. The highest acid uptake (190%) and proton conductivity (0.105S/cm at 180°C and 0% RH) were observed for phosphoric acide-dopped PBI nanocomposite membranes containing 8 wt% of SrCeO3 nanoparticles (PSC8). The PSC8 nanocomposite membranes were tested in a fuel cell and the polarization and power curves were obtained at different temperatures. The PSC8 showed 0.44W/cm2 power density and 0.88 A/cm2 current density in 0.5V at 180°C. The result obtained from our studies shows the enhanced potential of the PSC8 as proton exchange membranes for high temperature proton exchange membrane fuel cells.

Studies on the Use of N,N,N´,N´-Tetra(2-ethylhexyl) Diglycolamide (TEHDGA) for Actinide Partitioning. I: Investigation on Third-Phase Formation and Extraction Behavior

Diglycolamides have emerged as an interesting class of extractants for actinide partitioning from high-level waste (HLW). N,N,N´,N´-tetraoctyl diglycolamide (TODGA) has been extensively studied for lanthanide-actinide co-extraction behavior. The present work deals with a branched isomer of TODGA, that is, N,N,N´,N´-tetra(2-ethylhexyl) diglycolamide (TEHDGA). TEHDGA was studied for the extraction of 241Am and third-phase formation. The effect of using different phase modifiers on the prevention of the formation of a third phase during nitric acid extraction by TEHDGA along with the acid uptake behavior by TEHDGA in the presence of the modifiers was studied. The modifiers used for this purpose were di(n-hexyl)octanamide (DHOA), isodecanol, and n-decanol. The effect of the modifiers on the uptake of 241Am as a function of acid concentration and as a function of modifier concentration was also examined. DHOA was found to be a suitable modifier, in spite of its high acid uptake. The uptake of lanthanides Ce, La, Eu, Gd, and Nd and elements such as Fe, Ni, Mn, Mo, Ru, Sr, and Cs with DHOA-modified TEHDGA–n-dodecane solvent systems were investigated. The results obtained indicated that, while DHOA-modified TEHDGA/n-dodecane extracted lanthanides and actinides, it did not show any significant uptake of other elements. Thus, the TEHDGA-DHOA/n-dodecane solvent system can be used effectively for the partitioning of lanthanides and actinides from HLW.

Novel Polymer Electrolyte Membrane, Based on Pyridine Containing Poly(ether sulfone), for Application in High‐Temperature Fuel Cells

AbstractSummary: Novel poly(aryl ether sulfone) copolymers containing 2,5‐biphenylpyridine and tetramethyl biphenyl moieties were synthesized by polycondensation of 4‐fluorophenyl sulfone with 2,5‐(4′,4″ dihydroxy biphenyl)pyridine and tetramethyl biphenyl diol. Copolymers with different molecular weights and different monomer compositions were obtained. These copolymers exhibit excellent film‐forming properties, mechanical integrity, and high modulus up to 250 °C, high glass transition temperatures (above 280 °C) as well as high thermal stability up to 400 °C. In addition to the above properties required for PEMFC application, this novel material shows high oxidative stability and acid doping ability, enabling proton conductivity in the range of 10−2 S · cm−1 above 130 °C.Synthesis of copolymers with high acid uptake and ionic conductivity.magnified imageSynthesis of copolymers with high acid uptake and ionic conductivity.

The Sorption of Acids by Wool from Mixtures of Acids I—The Sorption of Hydrochloric Acid and Dichloroacetic Acid or Monochloroacetic Acid*

The amounts of dichloroacetic acid and hydrochloric acid sorbed by wool from mixtures containing various amounts of the two acids in aqueous solution were measured. Some tests were also carried out in which monochloroacetic acid was used instead of dichloroacetic. The results show that the dichloroacetate ion competes with the chloride ion for the sorption sites on the wool fibre, but its higher affinity causes a higher acid uptake than when hydrochloric acid alone is used at the same pH. The amount of acid sorbed can be calculated from the final concentrations of the two acids in the solution in equilibrium with the wool.