Sulfonated Poly(aryl sulfone)s Containing Ferrous and Ferric Ion Scavenger 1H-Imidazo[4,5-F][1,10]-phenanthroline Groups for Highly Durable Proton Exchange Membranes

Proton exchange membranes prepared from poly­(aryl sulfone)­s still need to overcome the drawbacks of chemical stability in acidic environments and low electrical conductivity due to water loss at high temperatures. Herein, we synthesized densely sulfonated poly­(aryl sulfone) proton exchange membranes containing a 1H-imidazo­[4,5-F]­[1,10]-phenanthroline moiety on the side chain with a metal ion coordination function. The coordination of 1H-imidazo­[4,5-F]­[1,10]-phenanthroline groups to metal ions can effectively prevent the formation of •OH radicals from homolytic cleavage of H2O2 catalyzed by metal ions. Since the conditions for the continuous formation of •OH radicals are fundamentally eliminated, the antioxidant stability of the membrane material is greatly improved. Mesoscale microscopic simulations showed that 1H-imidazo­[4,5-F]­[1,10]-phenanthroline has the effect of inducing phase separation, endowing the proton exchange membrane with a larger hydrophilic structural domain and possibly constructing a better connected channel for proton transport. Notably, these membranes can efficiently capture the Fe2+ and Fe3+ ions to form stable [Fe­(phen)3]2+ and [Fe­(phen)3]3+ interconnection points, respectively, which could not only enforce the water retention and the mechanical properties of the membranes but also serve as a catalyzed point to prevent H2O2 from undergoing homolytic cleavage and forming •OH radicals

Synthesis of Bis(amine anhydride)s for Novel High <i>T</i>_gs and Organosoluble Poly(amine imide)s by Palladium-Catalyzed Amination of 4-Chlorophthalide Anhydride

Two novel bis(amine anhydride)s, N,N-bis(3,4-dicarboxyphenyl)aniline dianhydride (I) and N,N-bis(3,4-dicarboxyphenyl)-p-tert-butylaniline (II), were synthesized from the palladium-catalyzed amination reaction of N-methyl-protected 4-chlorophthalic anhydride with arylamines, followed by alkaline hydrolysis of the intermediate bis(amine−phthalimide)s and subsequent dehydration of the resulting tetraacids. The X-ray structures of anhydride I and II were determined. The obtained dianhydride monomers were reacted with various aromatic diamines to produce a series of novel polyimides. Because of the incorporation of bulky, propeller-shaped triphenylamine units along the polymer backbone, all polyimides exhibited good solubility in many aprotic solvents while maintaining their high thermal properties. These polymers had glass transition temperatures in the range of 298−408 °C. Thermogravimetric analysis showed that all polymers were stable, with 10% weight loss recorded above 525 °C in nitrogen. The tough polymer films, obtained by casting from solution, had tensile strength, elongation at break, and tensile modulus values in the range of 95−164 MPa, 8.8−15.7%, and 1.3−2.2 GPa, respectively. The CO2 permeability coefficients (PCO2) and permeability selectivity of CO2 to CH4 (PCO2/PCH4) of these polyimide membranes were in the range of 7.8−274 barrer and 19.2−45.3, respectively

Heat-Treated Nonprecious Catalyst Using Fe and Nitrogen-Rich 2,3,7,8-Tetra(pyridin-2-yl)pyrazino[2,3-<i>g</i>]quinoxaline Coordinated Complex for Oxygen Reduction Reaction in PEM Fuel Cells

Pyrolyzed Fe/N/C catalysts were synthesized using a newly designed and synthesized 2,3,7,8-tetra(pyridin-2-yl)pyrazino[2,3-g]quinoxaline (TPPQ) organic compound as the nitrogen-containing ligand. The structure of TPPQ was deliberately designed to discourage the agglomeration of Fe during heat treatment as well as to provide a concentrated source of nitrogen. Catalysts were prepared by first coordinating TPPQ with Fe, forming Fe–TPPQ complexes, followed by impregnation onto carbon black (KJ600) and pyrolysis at 900 °C. Catalysts with 0.5%, 1%, 2%, 4%, and 8% initial iron content were prepared, and their physical characteristics were determined by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy analysis. Electrocatalytic activity toward the oxygen reduction reaction was evaluated and compared for all catalysts. The best performing catalyst was found to be the catalyst using 2% initial iron content. Evidence of iron metal and carbide particle formation was found for catalysts with initial iron content higher than 2%

Fe/N/C Electrocatalysts for Oxygen Reduction Reaction in PEM Fuel Cells Using Nitrogen-Rich Ligand as Precursor

High temperature pyrolysis can significantly improve the activity and stability of Fe-based catalysts. However, unwanted iron nanoparticles, which are proven inactive to oxygen reduction reaction (ORR), will form under this procedure. Herein, a nitrogen-rich and hindrance multifunctional 6,7-di­(pyridin-2-yl)­pteridine-2,4-diamine (DPPD) monomer was deliberately designed and synthesized. High content of thermally stable nitrogen in DPPD can increase the degree of coordination with iron and provide a high content of active nitrogen after pyrolysis. Distorted nitrogen-rich ferrous complex polymers were successfully prepared to keep iron ions well separated and prevent them from aggregating during the heat treatment. Carbon-supported Fe-based catalysts with different initial iron loadings from 0.2 to 4.0 wt % were obtained. Transmission electron microscopy (TEM) revealed that there were no obvious nanocrystals observed, even the initial iron loading was up to 2.0 wt %. The electrochemical performance of the Fe-based catalysts was evaluated via cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The result shows that an Fe-based catalyst with 2.0 wt % initial iron loading is the best ORR catalyst in acid media among all the iron loadings. Typically, in basic media, the catalyst with 2.0 wt % initial iron loading exhibits comparable electrocatalytic activity to commercial Pt/C material via an efficient four-electron-dominant ORR pathway coupled with better methanol tolerance as well as durability. XPS measurements confirmed that the outstanding activity of the catalyst with 2.0 wt % initial iron loading was likely attributed to higher content of pyridinic nitrogen, providing the highest density of active site structures

Alkaline Metal Oxide Assisting the Ionothermal Method for Efficient Fe‑N<i>_X</i>/C Catalyst Preparation

Owing to low cost and high efficiency, nonprecious metal catalysts have been widely used in various types of fuel cells. To obtain a high-activity electrocatalyst, a simple method for the synthesis of iron-modified covalent triazine frameworks by the direct heating of a mixture of FeCl3, ZnCl2, ZnO, and m-phthalodinitrile is reported. The role and a possible evolution pathway of the oxygen of metallic oxides are well discussed. To further verify our assumption, the Fe3O4 microspherical nanomaterials were synthesized and the relative Fe-based catalyst (Fe-NX/C) was successfully obtained by the ionothermal polymerization method. Fe-NX/C exhibits an extraordinary oxygen reduction reaction (ORR) performance in acidic solution, with a half-wave potential of only 25 mV negative shifts compared with Pt/C, while the power density is approximately 56% of that of Pt/C catalysts under the proton exchange membrane fuel cell testing condition. This work represents a new strategy to synthesize high-performance Fe-based catalysts toward ORR

Biologically Inspired Highly Durable Iron Phthalocyanine Catalysts for Oxygen Reduction Reaction in Polymer Electrolyte Membrane Fuel Cells

In the present work, we have designed and synthesized a new highly durable iron phtalocyanine based nonprecious oxygen reduction reaction (ORR) catalyst (Fe-SPc) for polymer electrolyte membrane fuel cells (PEMFCs). The Fe-SPc, with a novel structure inspired by that of naturally occurring oxygen activation catalysts, is prepared by a nonpyrolyzing method, allowing adequate control of the atomic structure and surface properties of the material. Significantly improved ORR stability of the Fe-SPc is observed compared with the commercial Fe-Pc catalysts. The Fe-SPc has similar activity to that of the commercial Fe-Pc initially, while the Fe-SPc displays 4.6 times higher current density than that of the commercial Fe-Pc after 10 sweep potential cycles, and a current density that is 7.4 times higher after 100 cycles. This has been attributed to the incorporation of electron-donating functional groups, along with a high degree of steric hindrance maintaining active site isolation. Nonprecious Fe-SPc is promising as a potential alternative ORR electrocatalyst for PEMFCs

Determination of Iron Active Sites in Pyrolyzed Iron-Based Catalysts for the Oxygen Reduction Reaction

Fe-based oxygen reduction reaction (ORR) catalyst materials are considered promising nonprecious alternatives to traditional platinum-based catalysts. These catalyst materials are generally produced by high-temperature pyrolysis treatments of readily available carbon, nitrogen, and iron sources. Adequate control of the structure and active site formation during pyrolysis methods is nearly impossible. Thus, the chemical nature, structure, and ORR mechanism of catalytically active sites in these materials is a subject of significant debate. We have proposed a method, utilizing CN^– ions as ORR inhibitors on Fe-based catalysts, to provide insight into the exact nature and chemistry of the catalytically active sites. Moreover, we propose two possible catalytically active site formation mechanisms occurring during high-temperature pyrolysis treatments, dependent on the specific type of precursor and synthesis methods utilized. We have further provided direct evidence of our proposed active site formations using ToF-SIMS negative and positive ion imaging. This knowledge will be beneficial to future work directed at the development of Fe-based catalysts with improved ORR activity and operational stabilities for fuel cell and battery applications

MXene/CNTs/Aramid Aerogels for Electromagnetic Interference Shielding and Joule Heating

It is a considerable challenge to develop a composite material with ultra-light and high electromagnetic interference (EMI) shielding efficiency for the next generation of electronic equipment. MXenes have received extensive attention in composite aerogel EMI shielding due to their abundant surface groups and ultra-high conductivity. However, the poor mechanical properties make them difficult to apply on a large scale. Here, we demonstrate a simple method to construct ultra-light conductive Ti3C2Tx MXene/aramid nanofibers (ANFs)/carbon nanotubes (CNTs) aerogels with a “sandwich” structure. CNTs and MXene absorb and reflect electromagnetic waves, while ANF aerogel provides good mechanical strength. Our composite aerogels with an extra-high EMI shielding efficiency of up to 69.0 dB at the X-band, despite their thickness and density being only 2 mm and 0.0428 g/cm3, respectively. At the same time, the composite aerogel with a low 0.0488 W/(m·K) thermal conductivity shows extraordinary flame resistance, heat preservation, and insulation ability. Besides, MXene/ANFs/CNTs aerogel can reach 104 °C in 3 s under an 8 V voltage and shows long-term Joule heating stability. This work provides a forward-looking idea for building multifunctional EMI shielding materials. The obtained aerogels have potential applications in aerospace, portable electronic devices, and defense industries

Performance Enhancement of Polymer Light-Emitting Diodes by Using Ultrathin Fluorinated Polyimide Modifying the Surface of Poly(3,4-ethylene dioxythiophene):Poly(styrenesulfonate)

Herein, an insulating fluorinated polyimide (F−PI) is utilized as an ultrathin buffer layer of poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) in polymer light-emitting diodes to enhance the device performance. The selective solubility of F−PI in common solvents avoids typical intermixing interfacial problems during the sequential multilayer spin-coating process. Compared to the control device, the F−PI modification causes the luminous and power efficiencies of the devices to be increased by a factor of 1.1 and 4.7, respectively, along with almost 3-fold device lifetime enhancement. Photovoltaic measurement, single-hole devices, and X-ray photoelectron spectroscopy are utilized to investigate the underlying mechanisms, and it is found that the hole injection barrier is lowered owing to the interactions between the PEDOT:PSS and F−PI. The F−PI modified PEDOT:PSS layer demonstrates step-up ionization potential profiles from the intrinsic bulk PEDOT:PSS side toward the F−PI-modified PEDOT:PSS surface, which facilitate the hole injection. Moreover, the insulating F−PI layer at the PEDOT:PSS surface is also favorable for the hole injection by blocking the electrons and strengthening the local electric field at the interface