Polybenzimidazole containing benzimidazole side groups for high-temperature fuel cell applications

Promoted Li+ Desolvation by the Reconstruction of Hydrogen-Bond Network in Functional Separator to Stabilize the Lithium Metal Anode Interface

High energy density lithium metal batteries (LMBs) are challenged by unstable interface reactions, leading to the continuous deterioration of parasitic reactions. To overcome this problem, here, new strategies are designed for promoting Li+ desolvation (PLD) separators with modulated hydrogen-bond network to stabilize the interfacial reaction. Experimental and computational results show that the difference in the electron cloud density distribution on the separator surface not only breaks the hydrogen-bond network of the conventional carbonate electrolyte, thus capturing the strongly dissolved ethylene carbonate (EC) but also realizes the promoted desolvation process of the outer Helmholtz plane (OHP). As a result, the Li+ desolvation barrier of the PLD separator decreases from 81.15 kJ to 73.01 kJ mol-1. The long cycle life of the assembled Li/Li symmetric cell with PLD separator can be extended to 4500 h at 3 mA cm-2/1.5 mAh cm-2. Notably, the LFP/Li full cell with the PLD separator even achieves a specific capacity of 94.2 mAh g-1 at a high rate of 7C. These results demonstrate that the PLD separator is capable of stabilizing interfacial reactions and enhancing the performance of high-rate LMBs, providing new ideas for further rational development in this field.

Characterization and Photofragmentation Studies of the Benzimidazole Homodimer: Evidence for Excited-State Charge-Coupled Proton Transfer

The spectroscopic characterization of the benzimidazole (BIM) homodimer was carried out in a molecular beam in the ground state as well as in the cationic state using the R2PI and RIDIR methods. Primarily, interest in the dimer was due to the observation of a proton-transferred BIM fragment at energies well below its thermodynamic threshold (i.e., barely above the ionization energy of the dimer where fragmentation was not expected). The detailed photofragmentation studies of the homodimer combined with spectroscopic observations and quantum chemical computations of the excited states established that the proton transfer from one subunit to the other occurs via conical intersections connecting the locally excited state, the charge-transfer state, and the ground state. In this study, we have also determined the N-H···N hydrogen bond dissociation energy in the ground state and in the cationic state to be 10.36 ± 0.14 and 27.55 ± 0.20 kcal mol^-1, respectively. Incidentally, this happens to be the first such report on the dissociation energy of the N-H···N hydrogen bond.

Polybenzimidazole/Nafion hybrid membrane with improved chemical stability for vanadium redox flow battery application

In order to increase the chemical stability of polybenzimidazole (PBI) membrane against the highly oxidizing environment of a vanadium redox flow battery (VRFB), PBI/Nafion hybrid membrane was developed by spray coating a Nafion ionomer onto one surface of the PBI membrane. The acid–base interaction between the sulfonic acid of the Nafion and the benzimidazole of the PBI created a stable interfacial adhesion between the Nafion layer and the PBI layer. The hybrid membrane showed an area resistance of 0.269 Ω cm² and a very low vanadium permeability of 1.95 × 10⁻⁹ cm² min⁻¹. The Nafion layer protected the PBI from chemical degradation under accelerated oxidizing conditions of 1 M VO₂⁺/5 M H₂SO₄, and this was subsequently examined in spectroscopic analysis. In the VRFB single cell performance test, the cell with the hybrid membrane showed better energy efficiency than the Nafion cell with 92.66% at 40 mA cm⁻² and 78.1% at 100 mA cm⁻² with no delamination observed between the Nafion layer and the PBI layer after the test was completed.

Novel polybenzimidazole (PBI)/Nafion hybrid membranes for the VRFB are made by spray coating a Nafion layer to protect PBI from chemical degradation.

Conformational preferences of monohydrated clusters of imidazole derivatives revisited

IR-UV double resonance spectroscopy was used to identify the conformers of monohydrated benzimidazole andN-methylbenzimidazole in a supersonic jet. A new OH–N bound conformer relevant to histidine containing proteins was discovered. The long standing differences in the literature about the relative energies and abundance of the monohydrated imidazole derivatives have also been resolved.

Synthesis of N-substituted poly(benzimidazole ketone ketone)s containing pyridine rings

Poly( N-arylenebenzimidazole ketone ketone pyridine)s have been prepared via N–C coupling reaction that removed the N–H sites from the novel bis(benzimidazoyl) derivatives with activated aromatic difluorides in sulfolane. The reaction was carried out at 210°C in the presence of anhydrous potassium carbonate. The structures of the polymers were characterized by means of Fourier transform infrared and proton nuclear magnetic resonance spectroscopies and elemental analysis. All resulting polymers showed essentially amorphous patterns. Differential scanning calorimetry and thermogravimetric measurements showed that the polymers had high glass transition temperatures (>179°C), good thermostability, and high decomposition temperatures (>401°C). These novel polymers also showed easy solubility.

Synthesis and characterization of para- and meta-polybenzimidazoles for high-temperature proton exchange membrane fuel cells

In this article, two polybenzimidazoles (PBIs) were synthesized by the polycondensation reaction of 3,3′-diaminobenzidine with terephthalic acid ( p-PBI) or isophthalic acid ( m-PBI) for application in high-temperature proton exchange membrane fuel cells. Two kinds of purification (P1, P2) were applied to clean the polymers. The chemical structure of PBI polymers was confirmed using Fourier transform infrared (FTIR) spectroscopy. Polymers after P1 can be soluble and cast into film only from hot sulfuric acid solution (H2SO4), whereas both polymers after P2 were soluble in dimethylacetamide solution. Polymer films cast from H2SO4 were investigated using FTIR. The thermal stabilities of PBIs and PBI films were studied using the thermogravimetric analysis and the first derivative of the TG method. The temperature of 5% weight loss ( T5%) for both PBIs ranges from 136 to 312°C under nitrogen atmosphere, depending on the dicarboxylic acid used and the kind of purification. The PBI films exhibited T5% at 55°C because of the protonation of nitrogen atom in PBI by hydrogen atom of hydroxyl group in H2SO4. Electrical behavior of the two polymers was tested using electrochemical impedance spectroscopy for gold (Au)/PBI/Au architecture. For both measured polymers, Nyquist plots are presented with fittings based on circuit models.