Boosting the proton conduction using protonated imidazole for advanced ion conducting membrane

Preparation of water-soluble imidazole-functionalized pillar[5]arenes: The activities of antibacterial and antioxidant, catalytic reduction of 4-nitrophenol

Macrocyclic supramolecular materials such as pillar[n]arenes play a prominent role in enhancing antibacterial activity through host-guest interactions. Herein, the water-soluble pillar[5]arene imidazole-1 and pillar[5]arene imidazole-2 were prepared, and their structure and chemical compositions were analyzed through multiple characterization methods. Afterward, the prepared imidazole-functionalized pillar[5]arenes were examined for antibacterial activity against Escherichia coli, Enterococcus faecalis, Staphylococcus aureus, and Salmonella typhimurium bacteria. Also, the antioxidant activities of the prepared imidazole-functionalized pillar[5]arenes were investigated using 2,2-Diphenyl-1-picrylhydrazyl. In addition, the catalytic activities of pillar[5]arene imidazole-1 and pillar[5]arene imidazole-2 by reduction of 4-nitrophenol were studied, indicating the catalytic reduction of 4-nitrophenol was 93.0 % for the pillar[5]arene imidazole-1 catalyst at 18 min. Comparison of the reactivity of pillar[5]arene imidazole-1 with that of pillar[5]arene imidazole-2 shows an increase in antibacterial and catalytic activity. This study summarized that using suitable catalysts, catalytic reduction aims to convert the most harmful and toxic organic compound 4-nitrophenol into non-toxic 4-aminophenol and popularize it in industry.

Proton Exchange Membrane with Dual-Active-Center Surpasses the Conventional Temperature Limitations of Fuel Cells

High temperature-proton exchange membrane fuel cells (HT-PEMFC) call for ionomers with low humidity dependence and elevated-temperature resistance. Traditional perfluorosulfonic acid (PFSA) ionomers encounter challenges in meeting these stringent requirements. Herein, this study reports a perfluoroimide multi-acid (PFMA) ionomer with dual active centers achieved through the incorporation of sulfonimide and phosphonic acid groups into the side chain. The fluorocarbon skeleton and multi-acid side chain structure facilitate the segregation of hydrophilic and hydrophobic microphases, augmenting the short-range ordering of hydrophilic nanodomains. Furthermore, the introduction of a rigid segment-benzene ring is employed to decrease side chain flexibility and raise the glass transition temperature. Notably, the prepared membrane exhibits a conductivity of 41 mS cm-1 at 40% relative humidity, showcasing a 1.8 times improvement over that of PFSA. Additionally, the power output of the H2-air fuel cell based on this membrane reaches 1.5 W cm-2 at 105 °C, marking a substantial 2.3 times enhancement compared to the PFSA. This work demonstrates the unique advantages of perfluorinated ionomers with multiple protogenic groups in the development of high-performance high-temperature electrolyte materials.

Triazole-rich 3D metal-organic framework incorporated solid electrolytes for superior proton conductivity and durability in fuel cells

Insufficient proton conductivity and oxidative stability of sulfonated hydrocarbons hinder their applicability as proton exchange membrane electrolytes in fuel cells. In this regard, fabrication of proton conducting mixed-matrix membranes (PC-MMMs) can be a superior approach to obtain desirable properties. In this work, a triazole ligand (1H-1,2,4 triazole) was coordinated to a zinc metal node to create a 3D metal-organic framework (MOF) and incorporated as an additive in a sulfonated poly(ether ether ketone) matrix at 1, 3, and 5 weight percentage to fabricate PC-MMMs by the casting process. Several characterization tools such as electrochemical impedance spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy were used to characterise these membranes and study their potential application as electrolyte(s) in PEMFCs (proton exchange membrane fuel cells). Membranes were also tested for water uptake, ion-exchange capacity and oxidative stability in Fenton's reagent. The performance of the polymeric composite membrane containing a 3 wt% MOF was then assessed in a H2/O2 single cell as it demonstrated the highest proton conductivity of 0.04 S cm-1 among all the compositions and a maximum current density of 1191 mA cm-2. The membrane was also subjected to an OCV hold test for 12 hours to study the chemical durability over a period of time. This report establishes that the inclusion of a triazole based MOF enhances the proton conductivity, performance, and thermal and chemical durability of composite membranes which can be considered as a promising electrolyte material at intermediate temperatures after a proper optimisation of different cell parameters.

Proton Conduction Mechanism for Anhydrous Imidazolium Hydrogen Succinate Based on Local Structures and Molecular Dynamics

Anhydrous organic crystalline materials incorporating imidazolium hydrogen succinate (Im-Suc), which exhibit high proton conduction even at temperatures above 100 °C, are attractive for elucidating proton conduction mechanisms toward the development of solid electrolytes for fuel cells. Herein, quantum chemical calculations were used to investigate the proton conduction mechanism in terms of hydrogen-bonding (H-bonding) changes and restricted molecular rotation in Im-Suc. The local H-bond structures for proton conduction were characterized by vibrational frequency analysis and compared with corresponding experimental data. The calculated potential energy surface involving proton transfer (PT) and imidazole (Im) rotational motion showed that PT between Im and succinic acid was a rate-limiting step for proton transport in Im-Suc and that proton conduction proceeded via the successive coupling of PT and Im rotational motion based on a Grotthuss-type mechanism. These findings provide molecular-level insights into proton conduction mechanisms for Im-based (or -incorporated) H-bonding organic proton conductors.