Ion-Exchange-Induced Selective Etching for the Synthesis of Amino-Functionalized Hollow Mesoporous Silica for Elevated-High-Temperature Fuel Cells

Advancements of Polyvinylpyrrolidone-Based Polymer Electrolyte Membranes for Electrochemical Energy Conversion and Storage Devices

Polymer electrolyte membranes (PEMs) play vital roles in electrochemical energy conversion and storage devices, such as polymer electrolyte membrane fuel cell (PEMFC), redox flow battery, and water electrolysis. As the crucial component of these devices, PEMs need to possess high ion conductivity and electronic insulation, remarkable mechanical and chemical stability, and outstanding isolation function for the materials on both sides of the cathode and anode. Polyvinylpyrrolidone has received widespread attention in the research of PEMs owing to its tertiary amine basic groups and exceptional hydrophilic properties. This review focuses on the application status of polyvinylpyrrolidone-based PEMs in PEMFC, vanadium redox flow battery, and alkaline water electrolysis, and describes in detail the key scientific problems in these fields, providing constructive suggestions and guidance for the application of polyvinylpyrrolidone-based PEMs in electrochemical energy conversion and storage devices.

Chiral Nanochannels of Ordered Mesoporous Silica Constructed by a Pillar[5]arene-Based Host-Guest System

The separation of racemic compounds by chiral nanochannels has attracted extensive attention. However, the fabrication of high-performance chiral nanochannels is still a challenge owing to the difficulty in magnifying the weak chiral interaction to macroscopic properties of materials. Herein, by introducing a l-alanine-pillar[5]arene host to achiral ordered mesoporous silica (OMS), chiral OMS nanochannels were fabricated, which exhibited excellent selectivity (ee value up to 90.2%) to separate racemic drugs with promising reusability and stability. Besides, it was identified that enantioselective separation took place through a molecular-recognition-adsorbed transport mechanism. This work highlights the great potential of chiral OMS nanochannels as a platform for enantioselective separation.

Novel proton conducting core-shell PAMPS-PVBS@Fe2TiO5 nanoparticles as a reinforcement for SPEEK based membranes

In this study, new nanocomposite membranes from sulfonated poly (ether ether ketone) (SPEEK) and proton-conducting Fe₂TiO₅ nanoparticles are prepared by the solution casting method. Sulfonated core–shell Fe₂TiO₅ nanoparticles are synthesized by redox polymerization. Therefore, 4-Vinyl benzene sulfonate (VBS) and 2-acrylamide-2-methyl-1-propane sulfonic acid (AMPS) are grafted on the surface of nanoparticles through radical polymerization. The different amounts of hybrid nanoparticles (PAMPS@Fe₂TiO₅ and PVBS@Fe₂TiO₅) are incorporated into the SPEEK matrix. The results show higher proton conductivity for all prepared nanocomposites than that of the SPEEK membrane. Embedding the sulfonated Fe₂TiO₅ nanoparticles into the SPEEK membrane improves proton conductivity by creating the new proton conducting sites. Besides, the nanocomposite membranes showed improved mechanical and dimensional stability in comparison with that of the SPEEK membrane. Also, the membranes including 2 wt% of PAMPS@Fe₂TiO₅ and PVBS@Fe₂TiO₅ nanoparticles indicate the maximum power density of 247 mW cm⁻² and 226 mW cm⁻² at 80 °C, respectively, which is higher than that of for the pristine membrane. Our prepared membranes have the potential for application in polymer electrolyte fuel cells.

Advancement toward Polymer Electrolyte Membrane Fuel Cells at Elevated Temperatures

Elevation of operational temperatures of polymer electrolyte membrane fuel cells (PEMFCs) has been demonstrated with phosphoric acid-doped polybenzimidazole (PA/PBI) membranes. The technical perspective of the technology is simplified construction and operation with possible integration with, e.g., methanol reformers. Toward this target, significant efforts have been made to develop acid-base polymer membranes, inorganic proton conductors, and organic-inorganic composite materials. This report is devoted to updating the recent progress of the development particularly of acid-doped PBI, phosphate-based solid inorganic proton conductors, and their composite electrolytes. Long-term stability of PBI membranes has been well documented, however, at typical temperatures of 160°C. Inorganic proton-conducting materials, e.g., alkali metal dihydrogen phosphates, heteropolyacids, tetravalent metal pyrophosphates, and phosphosilicates, exhibit significant proton conductivity at temperatures of up to 300°C but have so far found limited applications in the form of thin films. Composite membranes of PBI and phosphates, particularly in situ formed phosphosilicates in the polymer matrix, showed exceptionally stable conductivity at temperatures well above 200°C. Fuel cell tests at up to 260°C are reported operational with good tolerance of up to 16% CO in hydrogen, fast kinetics for direct methanol oxidation, and feasibility of nonprecious metal catalysts. The prospect and future exploration of new proton conductors based on phosphate immobilization and fuel cell technologies at temperatures above 200°C are discussed.

Bi-Functional Composting the Sulfonic Acid Based Proton Exchange Membrane for High Temperature Fuel Cell Application

Although sulfonic acid (SA)-based proton-exchange membranes (PEMs) dominate fuel cell applications at low temperature, while sulfonation on polymers would strongly decay the mechanical stability limit the applicable at elevated temperatures due to the strong dependence of proton conduction of SA on water. For the purpose of bifunctionally improving mechanical property and high-temperature performance, Nafion membrane, which is a commercial SA-based PEM, is composited with fabricated silica nanofibers with a three-dimensional network structure via electrospinning by considering the excellent water retention capacity of silica. The proton conductivity of the silica nanofiber–Nafion composite membrane at 110 °C is therefore almost doubled compared with that of a pristine Nafion membrane, while the mechanical stability of the composite Nafion membrane is enhanced by 44%. As a result, the fuel cell performance of the silica nanofiber-Nafion composite membrane measured at high temperature and low humidity is improved by 38%.