High temperature proton exchange membranes based on polybenzimidazoles for fuel cells

Eaton’s reagent in polybenzimidazole synthesis

The polycondensations of 3,3′-diaminobenzidine with two acids, 4,4′-oxybis(benzoic acid) and hexafluoroisopropylidene bis(benzoic acid), were conducted in Eaton’s reagent at the unusually high temperature of 180°C and under microwave irradiation at 90°C. Both protocols resulted in soluble polybenzimidazoles, OPBI and CF3PBI, of high molecular weights in very short reaction times. The synthesized polybenzimidazoles exhibited high thermostability and excellent mechanical properties. The influence of the reaction conditions on the polymer structure and molecular weights was studied. The “microwave effect” was demonstrated by comparison of the polycondensations conducted under microwave irradiation and conventional heating.

Polymer and Composite Membranes for Proton-Conducting, High-Temperature Fuel Cells: A Critical Review

Polymer fuel cells operating above 100 °C (High Temperature Polymer Electrolyte Membrane Fuel Cells, HT-PEMFCs) have gained large interest for their application to automobiles. The HT-PEMFC devices are typically made of membranes with poly(benzimidazoles), although other polymers, such as sulphonated poly(ether ether ketones) and pyridine-based materials have been reported. In this critical review, we address the state-of-the-art of membrane fabrication and their properties. A large number of papers of uneven quality has appeared in the literature during the last few years, so this review is limited to works that are judged as significant. Emphasis is put on proton transport and the physico-chemical mechanisms of proton conductivity.

Hierarchical Porous Polybenzimidazole Microsieves: An Efficient Architecture for Anhydrous Proton Transport via Polyionic Liquids

Liquid-induced phase-separation micromolding (LIPSμM) has been successfully used for manufacturing hierarchical porous polybenzimidazole (HPBI) microsieves (42-46% porosity, 30-40 μm thick) with a specific pore architecture (pattern of macropores: ∼9 μm in size, perforated, dispersed in a porous matrix with a 50-100 nm pore size). Using these microsieves, proton-exchange membranes were fabricated by the infiltration of a 1H-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide liquid and divinylbenzene (as a cross-linker), followed by in situ UV polymerization. Our approach relies on the separation of the ion conducting function from the structural support function. Thus, the polymeric ionic liquid (PIL) moiety plays the role of a proton conductor, whereas the HPBI microsieve ensures the mechanical resistance of the system. The influence of the porous support architecture on both proton transport performance and mechanical strength has been specifically investigated by means of comparison with straight macroporous (36% porosity) and randomly nanoporous (68% porosity) PBI counterparts. The most attractive results were obtained with the poly[1-(3H-imidazolium)ethylene]bis(trifluoromethanesulfonyl)imide PIL cross-linked with 1% divinylbenzene supported on HPBI membranes with a 21-μm-thick skin layer, achieving conductivity values up to 85 mS cm^-1 at 200 °C under anhydrous conditions and in the absence of mineral acids.

Cobaltocenium-containing polybenzimidazole polymers for alkaline anion exchange membrane applications

A novel cobaltocenium-containing polybenzimidazole polymer was used for alkaline anion exchange membranes.

On the nanosecond proton dynamics in phosphoric acid–benzimidazole and phosphoric acid–water mixtures

Combining ¹H-NMR, ¹⁷O-NMR, and high-resolution backscattering QENS hydrodynamic and structural proton transport in phosphoric acid is separated. The rate limiting steps for structural proton diffusion in mixtures of acid with Brønsted bases are found to occur below the nanosecond timescale.

Thin skinned asymmetric polybenzimidazole membranes with readily tunable morphologies for high-performance vanadium flow batteries

A series of thin skinned asymmetric polybenzimidazole membranes with readily tunable morphologies are fabricated for high-performance vanadium flow batteries.

Materials with high proton conductivity above 200 °C based on a nanoporous metal–organic framework and non-aqueous ionic media

MOF-based composite material features superior proton conductivity at temperatures above 200 °C in dry atmosphere.

Why do proton conducting polybenzimidazole phosphoric acid membranes perform well in high-temperature PEM fuel cells?

This ¹H-NMR, ³¹P-NMR, thermo-gravimetrical analysis, and conductivity study elucidates how hygroscopicity, acidity, and proton transport of phosphoric acid are affected by acid–base interactions with (benz)imidazole present in proton conducting high-temperature PEM fuel cell membranes.

Nitrile functionalized graphene oxide for highly selective sulfonated poly(arylene ether nitrile)-based proton-conducting membranes

The incorporation of 4-(3-aminophenoxy)phthalonitrile grafted graphene oxide into SPEN proton-conducting membrane was proved to be an effective way to improve the interfacial interaction and proton conductivity performance.

Proton conduction mechanisms in the phosphoric acid–water system (H4P2O7–H3PO4·2H2O): a 1H, 31P and 17O PFG-NMR and conductivity study

The exceptionally high structural proton conductivity in neat phosphoric acid (H₃PO₄), which is closely related to the topology of its frustrated hydrogen bond network, is a singularity in that its contribution to the total ionic conductivity decreases with both increasing and decreasing water content.

Constructing Straight Polyionic Liquid Microchannels for Fast Anhydrous Proton Transport

Polymeric ionic liquids (PILs) have triggered great interest as all solid-state flexible electrolytes because of safety and superior thermal, chemical, and electrochemical stability. It is of great importance to fabricate highly conductive electrolyte membranes capable to operate above 120 °C under anhydrous conditions and in the absence of mineral acids, without sacrificing the mechanical behavior. Herein, the diminished dimensional and mechanical stability of poly[1-(3H-imidazolium)ethylene]bis(trifluoromethanesulfonyl)imide has been improved thanks to its infiltration on a polybenzimidale (PBI) support with specific pore architecture. Our innovative solution is based on the synergic combination of an emerging class of materials and sustainable large-scale manufacturing techniques (UV polymerization and replication by microtransfer-molding). Following this approach, the PIL plays the proton conduction role, and the PBI microsieve (SPBI) mainly provides the mechanical reinforcement. Among the resulting electrolyte membranes, conductivity values above 50 mS·cm^-1 at 200 °C and 10.0 MPa as tensile stress are shown by straight microchannels of poly[1-(3H-imidazolium)ethylene]bis(trifluoromethanesulfonyl)imide cross-linked with 1% of dyvinylbenzene embedded in a PBI microsieve with well-defined porosity (36%) and pore diameter (17 μm).

Investigation of thermal and tensile properties of poly(benzimidazole-imide) composites incorporating salicylic acid–functionalized multiwalled carbon nanotubes

This work describes a novel aromatic poly(benzimidazole-imide) (PBII) with amino salicylic acid (ASA) segments in the main chain by melt/solid polymerization method under solvent-free conditions and its composites reinforced with ASA-functionalized multiwalled carbon nanotubes (MWCNTs-ASA). The polymer was obtained in high yield with an amorphous morphology, was soluble in various organic solvents, such as N,N′-dimethylacetamide, N,N′-dimethylformamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide, and could afford flexible and tough film via solution casting. MWCNT-ASA/PBII composite films were also prepared by casting a solution of precursor polymer containing different fractions of MWCNTs-ASA into a thin film (1, 2, and 5 wt%). The cast films exhibited good mechanical properties with tensile strengths of 90.00–128.3 MPa, elongation at break of 4.6–7.9%, and tensile modulus of 1.6–2.9 GPa. They were reasonably stable up to a temperature above 400°C for the PBII and above 450°C for the composites. Structural and morphological evaluation of the composites was carried out by Fourier transform infrared spectroscopy and X-ray diffraction. Dispersion of MWCNT-ASA in the polymer matrix was investigated by field emission scanning and transmission electron microscopy.

High Performance Palladium Supported on Nanoporous Carbon under Anhydrous Condition

Due to the high cost of polymer electrolyte fuel cells (PEFCs), replacing platinum (Pt) with some inexpensive metal was carried out. Here, we deposited palladium nanoparticles (Pd-NPs) on nanoporous carbon (NC) after wrapping by poly[2,2'-(2,6-pyridine)-5,5'-bibenzimidazole] (PyPBI) doped with phosphoric acid (PA) and the Pd-NPs size was successfully controlled by varying the weight ratio between Pd precursor and carbon support doped with PA. The membrane electrode assembly (MEA) fabricated from the optimized electrocatalyst with 0.05 mgPd cm-2 for both anode and cathode sides showed a power density of 76 mW cm-2 under 120 °C without any humidification, which was comparable to the commercial CB/Pt, 89 mW cm-2 with 0.45 mgPt cm-2 loaded in both anode and cathode. Meanwhile, the power density of hybrid MEA with 0.45 mgPt cm-2 in cathode and 0.05 mgPd cm-2 in anode reached 188 mW cm-2. The high performance of the Pt-free electrocatalyst was attributed to the porous structure enhancing the gas diffusion and the PyPBI-PA facilitating the proton conductivity in catalyst layer. Meanwhile, the durability of Pd electrocatalyst was enhanced by coating with acidic polymer. The newly fabricated Pt-free electrocatalyst is extremely promising for reducing the cost in the high-temperature PEFCs.

In-Situ Measurement of High-Temperature Proton Exchange Membrane Fuel Cell Stack Using Flexible Five-in-One Micro-Sensor

In the chemical reaction that proceeds in a high-temperature proton exchange membrane fuel cell stack (HT-PEMFC stack), the internal local temperature, voltage, pressure, flow and current nonuniformity may cause poor membrane material durability and nonuniform fuel distribution, thus influencing the performance and lifetime of the fuel cell stack. In this paper micro-electro-mechanical systems (MEMS) are utilized to develop a high-temperature electrochemical environment-resistant five-in-one micro-sensor embedded in the cathode channel plate of an HT-PEMFC stack, and materials and process parameters are appropriately selected to protect the micro-sensor against failure or destruction during long-term operation. In-situ measurement of the local temperature, voltage, pressure, flow and current distributions in the HT-PEMFC stack is carried out. This integrated micro-sensor has five functions, and is favorably characterized by small size, good acid resistance and temperature resistance, quick response, real-time measurement, and the goal is being able to be put in any place for measurement without affecting the performance of the battery.

Improved Electrodes for High Temperature Proton Exchange Membrane Fuel Cells using Carbon Nanospheres

This work evaluates the use of carbon nanospheres (CNS) in microporous layers (MPL) of high temperature proton exchange membrane fuel cell (HT-PEMFC) electrodes and compares the characteristics and performance with those obtained using conventional MPL based on carbon black. XRD, hydrophobicity, Brunauer-Emmett-Teller theory, and gas permeability of MPL prepared with CNS were the parameters evaluated. In addition, a short life test in a fuel cell was carried out to evaluate performance under accelerated stress conditions. The results demonstrate that CNS is a promising alternative to traditional carbonaceous materials because of its high electrochemical stability and good electrical conductivity, suitable to be used in this technology.