Novel polyimides containing benzimidazole for temperature proton exchange membrane fuel

In Silico Demonstration of Fast Anhydrous Proton Conduction on Graphanol

Development of new materials capable of conducting protons in the absence of water is crucial for improving the performance, reducing the cost, and extending the operating conditions for proton exchange membrane fuel cells. We present detailed atomistic simulations showing that graphanol (hydroxylated graphane) will conduct protons anhydrously with very low diffusion barriers. We developed a deep learning potential (DP) for graphanol that has near-density functional theory accuracy but requires a very small fraction of the computational cost. We used our DP to calculate proton self-diffusion coefficients as a function of temperature, to estimate the overall barrier to proton diffusion, and to characterize the impact of thermal fluctuations as a function of system size. We propose and test a detailed mechanism for proton conduction on the surface of graphanol. We show that protons can rapidly hop along Grotthuss chains containing several hydroxyl groups aligned such that hydrogen bonds allow for conduction of protons forward and backward along the chain without hydroxyl group rotation. Long-range proton transport only takes place as new Grotthuss chains are formed by rotation of one or more hydroxyl groups in the chain. Thus, the overall diffusion barrier consists of a convolution of the intrinsic proton hopping barrier and the intrinsic hydroxyl rotation barrier. Our results provide a set of design rules for developing new anhydrous proton conducting membranes with even lower diffusion barriers.

Sulfonated Polysulfone/TiO2(B) Nanowires Composite Membranes as Polymer Electrolytes in Fuel Cells

New proton conducting membranes based on sulfonated polysulfone (sPSU) reinforced with TiO₂(B) nanowires (1, 2, 5 and 10 wt.%) were synthesized and characterized. TiO₂(B) nanowires were synthesized by means of a hydrothermal method by mixing TiO₂ precursor in aqueous solution of NaOH as solvent. The presence of the TiO₂(B) nanowires into the polymer were confirmed by means of Field Emission Scanning Electron Microscopy, Fourier transform infrared and X-ray diffraction. The thermal study showed an increase of almost 20 °C in the maximum temperature of sPSU backbone decomposition due to the presence of 10 wt.% TiO₂(B) nanowires. Water uptake also is improved with the presence of hydrophilic TiO₂(B) nanowires. Proton conductivity of sPSU with 10 wt.% TiO₂(B) nanowires was 21 mS cm⁻¹ (at 85 °C and 100% RH). Under these experimental conditions the power density was 350 mW cm⁻² similar to the value obtained for Nafion 117. Considering all these obtained results, the composite membrane doped with 10 wt.% TiO₂(B) nanowires is a promising candidate as proton exchange electrolyte in fuel cells (PEMFCs), especially those operating at high temperatures.

The effects of long and bulky aromatic pendent groups with flexible linkages on the thermal, mechanical and electrical properties of the polyimides and their nanocomposites with functionalized silica

A novel diamine bis(4-aminophenyl)bis{3,4[(4-(8-quinolyloxymethyl carbonyl)]}methane, containing two long/bulky aromatic pendent chains was synthesized by incorporating aromatic and hetero aromatic groups with flexible linkages. Flexible, stretchable, thermally stable and processable polyimides were prepared by reacting this newly synthesized diamine with commercial tetracarboxylic acid dianhydrides like 3,3',4,4'-benzophenone tetra carboxylic acid dianhydride (BTDA) and 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic Anhydride (BPADA). Nanocomposites of polyimides were prepared using aromatic amine functionalized silica as a filler by solution casting method. The current work investigates the effects of incorporating long/bulky aromatic side chains and flexible linkages on the thermal, mechanical, electrical and optical properties of the polyimides and nanocomposites. The polyimides showed good thermal stability (T 10% = 364 & 388), high flame resistance, low glass transition temperatures (T g = 130 °C & 156 °C), very low dielectric constants (2.5 & 2.8 at 1 MHz) and good optical transparency. The neat polyimides displayed good elongation at break (133-155%) but possessed low tensile strength. The chemically imidized polyimides showed good solubility in low and high boiling solvents. Nanocomposites of polyimides based on aromatic amine functionalized silica exhibited enhanced properties with T 10% values varying between 409-482 °C, T g between 165-280 °C and higher dielectric constants (3-5.7 at 1 MHz).

Synthesis and Properties of Poly(imides) and Poly(imides)/Ionic Liquid Composites Bearing a Benzimidazole Moiety

Three new aromatic poly(imides) containing benzimidazole units in the backbone were synthesized and characterized by several spectroscopic techniques. Flexible spacer groups were incorporated into the poly(imides) structure to improve their solubility in organic solvents and their oxidative stabilization. All poly(imides) were thermally stable (T_d5% > 512 °C) and had the ability to form dense flexible films. Novel composite films were successfully prepared by loading poly(imide) with ionic liquid ([Bmim]Br) at different concentrations up to 25 wt.%. The resulting materials were characterized according to their morphology and elemental composition (SEM-EDX), water uptake capability, contact angle, and oxidative degradation resistance. Results suggested that poly(imide)/ionic liquid composites would be excellent candidates for future proton conductivity measurements.

Mixed Rigid and Flexible Component Design for High-Performance Polyimide Films

To develop the polyimide (PI) which is closely matched to the coefficient of the thermal expansion (CTE) of copper, a series of PIs are prepared from 5,4′-diamino-2-phenyl benzimidazole (DAPBI), 4,4′-diaminodiphenyl ether (ODA), and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) using a sequential copolymerization, blade coating, and thermal imidization process. The physical properties of the PIs are effectively regulated and optimized by adjusting the ratio of the rigid DAPBI and flexible ODA components. By increasing the DAPBI content, thermal stability, dimensional stability, and mechanical properties, the resultant polymer is enhanced. PI-80 exhibits an excellent comprehensive performance, a glass transition temperature of 370 °C, and a tensile strength of 210 MPa. Furthermore, the CTE as calculated in the range 50–250 °C is ca. 19 ppm/K, which is equal to that of copper. A highly dimensionally stable, curl-free, and high T-style peel strength (6.4 N/cm) of copper/PI laminate was obtained by casting the polyamic acid onto copper foil (13 μm) and thermally curing at 360 °C, which indicates that it has the potential to be applied as an electronic film for flexible displays and flexible printed circuit boards. A structural rationalization for these remarkable properties is also presented.

Graphene oxide based nanohybrid proton exchange membranes for fuel cell applications: An overview

In the context of many applications, such as polymer composites, energy-related materials, sensors, 'paper'-like materials, field-effect transistors (FET), and biomedical applications, chemically modified graphene was broadly studied during the last decade, due to its excellent electrical, mechanical, and thermal properties. The presence of reactive oxygen functional groups in the grapheme oxide (GO) responsible for chemical functionalization makes it a good candidate for diversified applications. The main objectives for developing a GO based nanohybrid proton exchange membrane (PEM) include: improved self-humidification (water retention ability), reduced fuel crossover (electro-osmotic drag), improved stabilities (mechanical, thermal, and chemical), enhanced proton conductivity, and processability for the preparation of membrane-electrode assembly. Research carried on this topic may be divided into protocols for covalent grafting of functional groups on GO matrix, preparation of free-standing PEM or choice of suitable polymer matrix, covalent or hydrogen bonding between GO and polymer matrix etc. Herein, we present a brief literature survey on GO based nano-hybrid PEM for fuel cell applications. Different protocols were adopted to produce functionalized GO based materials and prepare their free-standing film or disperse these materials in various polymer matrices with suitable interactions. This review article critically discussed the suitability of these PEMs for fuel cell applications in terms of the dependency of the intrinsic properties of nanohybrid PEMs. Potential applications of these nanohybrid PEMs, and current challenges are also provided along with future guidelines for developing GO based nanohybrid PEMs as promising materials for fuel cell applications.

Synthesis and characterization of novel imidazolium-functionalized polyimides for high temperature proton exchange membrane fuel cells

PEMFCs based on novel imidazolium-functionalized polyimides (ImPI-x)s demonstrate high OCVs and high peak power density with low PA uptakes. Microphase separation of ImPI-x can also be observed by AFM.