Proton Conductivity Properties Research Articles

Construction and Comparative Research of Two MOFs Proton Conducting Materials Containing Nitro Groups.

In field of electrochemistry, there has been a growing interest in the potential applications of proton-conducting metal-organic frameworks (MOFs). Therefore, how to design and synthesize MOFs with high proton conductivity is considered crucial. In this study, two examples of nitro-containing Cd-based MOFs, MOF-1 {[Cd3(TIPE)1.5(NO3)5Cl(H2O)2]·17H2O}n and MOF-2 {[Cd(TIPE)0.5(nip)]·10H2O}n (TIPE=1,1,2,2-tetrakis(4-(1H-imidazole-1-yl)phenyl)ethene, H2nip=5-Nitroisophthalic Acid), had been successfully designed and synthesized, and their proton-conducting properties were thoroughly investigated. Notably, both materials displayed peak proton conductivity at 98% RH and 90 °C, exhibiting values of 9.13 × 10-3 and 3.00 × 10-3 S∙cm-1 for MOF-1 and MOF-2, respectively. The plausible proton conduction pathways and mechanisms were elucidated through structural analyses, water vapor adsorption studies, and the determination of activation energy (Ea) values. It was found that the difference in proton conductivity between MOF-1 and MOF-2 was mainly associated with the different water absorption rates of the samples. The uniqueness of this study was that for the first time conducted an in-depth study of the role of nitrate in proton conduction, providing new ideas for designing materials with excellent proton conductivity.

Continuous Graded Catalyst Layers for PEM Fuel Cells with Improved Humidity Range Tolerance

Abstract Grading electrodes is a promising approach to reduce ohmic and mass transport-related voltage losses in proton exchange membrane fuel cells. In graded electrodes, the ionomer and/or catalyst are spatially non-uniformly distributed to optimize performance over a wide operating range. In this study, through-plane ionomer gradients were fabricated with a simple wet-layer deposition technique that can readily be adapted in a roll-to-roll process. The presence of ionomer gradients was verified using scanning transmission electron microscopy and the profiles were found to be continuous despite using only two coating steps. Single cell tests revealed that the gradients outperform conventional electrodes and maintain the optimal performance for different relative humidities. These improvements were traced back to enhanced mass transport and protonic conduction properties identified by detailed electrochemical analysis. This manufacturing approach for electrodes offers an accessible toolbox to produce versatile and specialized multi-layered catalyst layers for different applications.

Controllable Synthesis and Ultrahigh Proton Conduction of a Hydrogen-Bond Network.

The functionalization of polyoxometalates with organic ligands provides a new-style strategy to accurately incorporate polyoxometalates with advanced functional organic moieties on their surfaces, the development of which has attracted increasing research interest due to the potential applications. A germanium tungstate Na2(H3O)6[{RuIV(bpy)}2{WO2(C2O4)}2(GeW11O39)2]·27H2O (bpy = 2,2'-bipyridine) with two ligands covalently modified was triumphantly synthesized, using the conventional one-pot hydrothermal method. It was systematically characterized by thermogravimetric analysis (TGA), elemental analysis, infrared (IR) spectroscopy, single-crystal X-ray diffraction, X-ray photoelectron spectroscopy (XPS), powder diffraction (PXRD), scanning electronic microscopy (SEM), and ultraviolet-visible (UV-vis) spectroscopy. The two-dimensional (2D) layered structure was established through hydrogen bonding and Na+ bridges. Impedance measurements indicate that it displays outstanding proton conduction properties, with a splendid conductivity up to 1.24 × 10-2 S·cm-1 under 353 K and 90% relative humidity (RH), owing to the rich interlayer hydrogen-bond network formed by the organic ligands ({RuC10H8N2}4+ and {WC2O4}4+), hydrated protons (H3O+), and crystal waters.

Conversion of Carbon Dioxide into Molecular-based Porous Frameworks.

ConspectusThe conversion of carbon dioxide (CO2) to value-added functional materials is a major challenge in realizing a carbon-neutral society. Although CO2 is an attractive renewable carbon resource with high natural abundance, its chemical inertness has made the conversion of CO2 into materials with the desired structures and functionality difficult. Molecular-based porous materials, such as metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs), are designable porous solids constructed from molecular-based building units. While MOF/COFs attract wide attention as functional porous materials, the synthetic methods to convert CO2 into MOF/COFs have been unexplored due to the lack of synthetic guidelines for converting CO2 into molecular-based building units.In this Account, we describe state-of-the-art studies on the conversion of CO2 into MOF/COFs. First, we outline the key design principles of CO2-derived molecular building units for the construction of porous structures. The appropriate design of reactivity and the positioning of bridging sites in CO2-derived molecular building units is essential for constructing CO2-derived MOF/COFs with desired structures and properties. The synthesis of CO2-derived MOF/COFs involves both the transformation of CO2 into building units and the formation of extended structures of the MOF/COFs. We categorized the synthetic methods into three types as follows: a one-step synthesis (Type-I); a one-pot synthesis without workup (Type-II); and a multistep synthesis which needs workup (Type-III).We demonstrate that borohydride can convert CO2 into formate and formylhydroborate that serve as a bridging linker for MOFs in the Type-I and Type-II synthesis, representing the first examples of CO2-derived MOFs. The electronegativity of coexisting metal ions determines the selective conversion of CO2 into formate and formylhydroborate. Formylhydroborate-based MOFs exhibit flexible pore sizes controlled by the pressure of CO2 during synthesis. In pursuit of highly porous structures, we present the Type-I synthesis of MOFs from CO2 via the in situ transformation of CO2 into carbamate linkers by amines. The direct conversion of diluted CO2 (400 ppm) in air into carbamate-based MOFs is also feasible. Coordination interactions stabilize the intrinsically labile carbamate in the MOF lattice. A recent study demonstrates that the Type-III synthesis using alkynylsilane precursors enables the synthesis of highly porous and stable carboxylate-based MOFs from CO2, which exhibit catalytic activity in CO2 conversion. We also extended the synthesis of MOFs from CO2 to COFs. The Type-III synthesis using a formamide monomer affords stable CO2-derived COFs showing proton conduction properties. The precise design of CO2-derived building units enables expansion of the structures and functionalities of CO2-derived MOF/COFs. Finally, we propose future challenges in this field: (i) expanding structural diversity through synthesis using external fields and (ii) exploring unique functionalities of CO2-derived MOF/COFs, such as carriers for CO2 capture and precursors for CO2 transformation. We anticipate that this Account will lay the foundation for exploring new chemistry of the conversion of CO2 into porous materials.

High-performance proton exchange membrane derived from N-heterocycle poly(aryl ether sulfone)s with ether-free hydrophilic blocks and exhibiting good stability and proton-conducting performance

The trade-off issue between proton conduction properties and stability is a constraint on the commercial application of non-fluorinated proton exchange membranes for fuel cells. To alleviate the issue, the multi-block N-heterocycle poly(aryl ether sulfone)s with ether-free hydrophilic blocks (b-SPDPESs), which is composited by diphenyl sulfone moieties and biphthalazindione structures with dense pendant benzenesulfonic groups, are developed to prepare high-performance membranes. The self-assembly effect of block copolymers not only improves the membrane stability but also constructs regular proton conduction channels. Moreover, the conduction channel consists of hydrophilic blocks without ether bonds, which effectively improves the tolerance of the membrane to radicals. The hydrogen-bond network between sulfonic groups and N-heterocycles in the channel improves the proton conduction efficiency, inhibits the swelling of the membrane, and improves the stability of the membrane. As a result, the swelling degree of b-SPDPESs membrane is only 15.8 %, the proton conductivity is as high as 238 mS cm−1, the membrane aging broken time at 80 °C is between 4 and 6.6 h, and the fuel cells loading the membranes and feeding with hydrogen and air perform the max power density of between 0.65 and 1.25 W cm−2. Modulating the sequence structure of chains and constructing multiblock polymers containing ether-free N-heretrocyclic blocks with sulfonic groups improve the stability of membranes while ensuring their proton conductivity.

Porous Metal Phosphonate Frameworks: Construction and Physical Properties.

ConspectusPorous metal phosphonate frameworks (PMPFs) as a subclass of metal-organic frameworks (MOFs) have promising applications in the fields of gas adsorption and separation, ion exchange and storage, catalysis, sensing, etc. Compared to the typical carboxylate-based MOFs, PMPFs exhibit higher thermal and water stability due to the strong coordination ability of the phosphonate ligands. Despite their robust frameworks, PMPFs account for less than 0.51% of the porous MOFs reported so far. This is because metal phosphonates are highly susceptible to the formation of dense layered or pillared-layered structures, and they precipitate easily and are difficult to crystallize. There is a tendency to use phosphonate ligands containing multiple phosphonate groups and large organic spacers to prevent the formation of dense structures and generate open frameworks with permanent porosity. Thus, many PMPFs are composed of chains or clusters of inorganic metal phosphonates interconnected by organic spacers. Using this feature, a wide range of metal ions and organic components can be selected, and their physical properties can be modulated. However, limited by the small number of PMPFs, there are still relatively few studies on the physical properties of PMPFs, some of which merely remain in the description of the phenomena and lack in-depth elaboration of the structure-property relationship. In this Account, we review the strategies for constructing PMPFs and their physical properties, primarily based on our own research. The construction strategies are categorized according to the number (n = 1-4) of phosphonate groups in the ligand. The physical properties include proton conduction, electrical conduction, magnetism, and photoluminescence properties. Proton conductivity of PMPFs can be enhanced by increasing the proton carrier concentration and mobility. The former can be achieved by adding acidic groups such as -POH and/or introducing acidic guests in the hydrophilic channels. The latter can be attained by introducing conjugate acid-base pairs or elevating the temperature. Semiconducting PMPFs, on the other hand, can be obtained by constructing highly conjugated networks of coordination bonds or introducing large conjugated organic linkers π-π stacked in the lattice. In the case of magnetic PMPFs, long-range magnetic ordering occurs at very low temperatures due to very weak magnetic exchange couplings propagated via O-P-O and/or O(P) units. However, lanthanide compounds may be interesting candidates for single-molecule magnets because of the strong single-ion magnetic anisotropy arising from the spin-orbit coupling and large magnetic moments of lanthanide ions. The luminescent properties of PMPFs depend on the metal ions and/or organic ligands. Emissive PMPFs containing lanthanides and/or uranyl ions are promising for sensing and photonic applications. We conclude with an outlook on the opportunities and challenges for the future development of this promising field.

Anisotropic Superprotonic Conduction in a Layered Single-Component Hydrogen-Bonded Organic Framework with Multiple In-Plane Open Channels.

Hydrogen-bonded organic frameworks (HOFs) are promising proton conductive materials because of their inherent and abundant hydrogen-bonding sites. However, most superprotonic-conductive HOFs are constructed from multiple components to enable favorable framework architectures and structural integrity. In this contribution, layered HOF-TPB-A3 with a single component is synthesized and exfoliated. The exfoliated nanoplates exhibited anisotropic superprotonic conduction, with in-plane proton conductivities reaching 1.34×10-2 S cm-1 at 296 K and 98% relative humidity (RH). This outperforms the previously reported single-component HOFs and is comparable with the state-of-the-art multiple-component HOFs. The high and anisotropic proton conductive properties can be attributed to the efficient proton transport along multiple open channels parallel to their basal planes. Moreover, an all-solid-state (ASS) proton rectifier device is demonstrated by combining HOF-TPB-A3 and a hydroxide ion-conducting layered double hydroxide (LDH). This work suggests that single-component HOFs with multiple open channels offer more opportunities as versatile platforms for proton conductors, making them promising candidates for conducting media in protonic devices.

Dual-Template-Directed Zero-Dimensional Bismuth Chlorides: Structures, Luminescence, Photoinduced Chromism, and Enhanced Proton Conductivity.

Zero-dimensional (0D) hybrid organic-inorganic bismuth halides have attracted immense scientific interest as promising candidates for lead-free materials. Here, by using a typical solvothermal method, two mixed-cation-phase 0D hybrid bismuth chlorides of [HPDA][H2PDA]BiCl6 (1) and [Hbzim][H2PA]BiCl6 (2) (PDA = bis(4-pyridyl)amine, bzim = benzimidazole, PA = 2-picolylamine) have been assembled based on a series of organic amine guests. Both compounds exhibit interesting photoluminescence phenomena, in which compound 1 exhibits a double emission property of blue fluorescence and yellow-green phosphorescence simultaneously, while compound 2 exhibits wide-band yellow-green emission under visible light excitation. The luminescence mechanism is explained by experiments and theoretical calculations. In view of the fact that halometallate units and the conjugated nitrogen heterocyclic systems can act as electron donors and electron acceptors, respectively, both compounds exhibit free radical-driven photochromism induced by electron transfer under xenon lamp irradiation at room temperature. In addition, benefiting from abundant hydrogen bond networks in structures, the two compounds show significant temperature-dependent proton conduction behavior in the range of 298-343 K, and the proton conductivity of both compounds is significantly improved after light irradiation. Our study demonstrates two novel hybrid mixed-cation-phase 0D hybrid bismuth halides with photoluminescence, photochromism, and photomodulated proton conduction properties, which enriches the dual-template-directed metal halide system and provides a feasible scheme for the synthesis of photoresponsive smart materials.

Structural Landscape and Proton Conduction of Lanthanide 5-(Dihydroxyphosphoryl)isophthalates.

Metal phosphonate-carboxylate compounds represent a promising class of materials for proton conduction applications. This study investigates the structural, thermal, and proton conduction properties of three groups of lanthanide-based compounds derived from 5-(dihydroxyphosphoryl)isophthalic acid (PiPhtA). The crystal structures, solved ab initio from X-ray powder diffraction data, reveal that groups Ln-I, Ln[O3P-C6H3(COO)(COOH)(H2O)2] (Ln = La, Pr), and Ln-II, Ln2{[O3P-C6H3(COO)(COOH)]2(H2O)4}·2H2O (Ln = La, Pr, Eu), exhibit three-dimensional frameworks, while group Ln-III, Ln[O3P-C6H3(COO)(COOH)(H2O)] (Ln = Yb), adopts a layered structure with unbonded carboxylic groups oriented toward the interlayer region. All compounds feature carboxylic groups and coordinating water molecules. Impedance measurements demonstrate that these materials exhibit water-mediated proton conductivity, initially following a vehicle-type proton-transfer mechanism. Upon exposure to ammonia vapors from a 14 or 28% aqueous solution, compounds from groups II and III adsorb ammonia and water, leading to an enhancement in proton conductivity consistent with a Grotthuss-type proton-transfer mechanism. Notably, group II of the studied compounds undergoes the formation of a new expanded phase through the internal reaction of carboxylic groups with ammonia, coexisting with the as-synthesized phase. This postsynthetic modification results in a significant increase in proton conductivity, from approximately ∼5 × 10-6 to ∼10-4 S·cm-1 at 80 °C and 95% relative humidity (RH), attributed to a mixed intrinsic/extrinsic contribution. Remarkably, the NH3(28%)-exposed Yb-III compound achieves an enhancement in proton conductivity, reaching ∼ 5 × 10-3 S·cm-1 at 80 °C and 95% RH, primarily through an extrinsic contribution.

Metalo Hydrogen-Bonded Organic Frameworks Constructed by Coordinated Chains for Magnetic and Proton-Conductive Bifunctionality.

Metalo hydrogen-bonded organic frameworks (MHOFs) have received growing interest in designing crystalline functional materials. However, reports on bifunctional MHOFs showing magnetic and proton-conductive properties are extremely limited and their design is challenging. Herein, we investigated the magnetic and proton-conductive properties of two sulfonated CoHOF and MnHOF, {M(H2O)2(abs)2}n (M = Co2+ and Mn2+, Habs = 4-aminoazobenzene-4'-sulfonic anion), constructed by coordination chains. The supramolecular frameworks sustained by H bonds between -SO3- and coordinated water show directional ladder-type H bonds with hydrophilic nanochannels, leading to high proton conduction with exceptionally high conductivity around 10-2 S cm-1 at 100 °C under 97% relative humidity. In particular, the maximum σ value of CoHOF, 2.11 × 10-2 S cm-1, recorded the highest value among the reported proton-conducting materials showing slow magnetic relaxation. Meanwhile, the molecular structure of organosulfonate enables the magnetic isolation of high-spin Co2+ and Mn2+ centers in the frameworks. Magnetic measurements indicated that the MHOFs show field-induced single-ion magnet (SIM) properties, making these compounds rare magnetic-proton-conductive MHOFs. The work provides not only two unique MHOFs with SIM behavior and high proton conduction performance but also avenues for designing stable bifunctional MHOFs via a coordination chain approach.

Design and assembly of conductive covalent organic frameworks for proton exchange membrane application

To develop proton exchange membranes (PEMs) with robust structure stability and remarkable proton conductivity and explore their application in PEMs fuel cells have significant implications for realizing reduced carbon emission and environmental pollution. Covalent organic frameworks (COFs), as crystalline porous polymer material composed of organic monomers and connected by covalent bond, possess specific framework, inherent porosity, adjustable functional group and eminent thermal/chemical structure stability. Therefore, COFs display prominent superiorities in constructing rigid ordered proton transfer channels and improving fuel cell performance long‐term durability. In this review, the proton conduction properties of extrinsic proton‐conductive COFs (incorporating carriers into the pore), intrinsic proton‐conductive COFs (introducing conductive groups on the backbone) and combined extrinsic/intrinsic proton‐conductive COFs in the form of pressed pellets are discussed in detail. Meanwhile, proton‐conductive COFs related PEMs, including COFs‐related polymer‐based composite membranes, COFs‐based composite membranes and self‐supporting COFs membranes are also systematically summarized. In addition, the existing challenges are analyzed and future outlooks are addressed.

[Ce2(H2PO3)(C2O4)4](C6N2H16)·H3O·3H2O: A lanthanide phosphite-oxalate compound with high proton conductivity

A new cerium phosphite-oxalate, [Ce2(H2PO3)(C2O4)4](C6N2H16)·H3O·3H2O (1), was prepared under solvothermal condition using 1-ethylpiperazine as template. Single-crystal X-ray diffraction proves that compound 1 has a new three-dimensional (3D) structure constructed with CeO9 polyhedra, [C2O42−] ligands and [H2PO3−] groups. View along the b-axis, 1-ethylpiperazine cations and water molecules alternately located in the adjacent 12-ring channels. Impedance analysis shows that the proton conductivity of 1 is up to 9.17 × 10−4 S cm−1 at 75 °C and 98 % relative humidity (RH). Stability test reveals that proton conduction has good persistence at the highest temperature and humidity. This suggests that compound 1 possesses promising proton conductivity property, making it into a potential candidate material for proton exchange membranes.

Proton-conductive properties of a stable three-dimensional aluminum(III)-organic framework constructed by porphyrinlcarboxylate

The proton conductivity (σ) of the highly stable metal-organic frameworks (MOFs) built by carboxylic acid ligand and aluminum metal has not been fully investigated. Herein, a three-dimensional aluminum-based MOF, [(AlOH)2TCPP]n (namely Al-TCPP) with exceptional structural stability was solvothermally synthesized using an organic multifunctional bridging ligand, meso-tetra(4-carboxyphenyl)porphine (H4TCPP) with a large stiff ring structure and Al(NO3)3⋅9H2O as raw materials. The dependency of σ on temperature and relative humidity (RH) was surveyed using the AC impedance test after the MOF's thermal, water, and chemical stabilities, as well as nitrogen and H2O vapor adsorptions, were all characterized. Experimental results demonstrated that this highly stable MOF with a high specific surface area exhibited impressive proton conductivity, with an optimal σ of 3.2 × 10-4 S/cm under 100 °C/98% RH. Furthermore, the proton-conducting mechanism inside the framework was highlighted using computed activation energy and structural analysis. This study provides new inspiration for designing and searching for high-performance proton-conductive materials.

UiO‐66‐NH2 anchored sulfonated polyphenylene sulfide proton exchange membrane with high proton conductivity and low methanol permeability

AbstractThis study loaded different amounts of UiO‐66‐NH2 onto sulfonated polyphenylene sulfide fibers (SPPS), successfully loading UiO‐66‐NH2 on SPPS fibers confirmed by energy dispersive x‐ray spectroscopy, x‐ray diffraction, and Fourier transform infrared spectroscopy. The UiO‐66‐NH2‐X@SFM were then impregnated in Nafion solution to obtain UiO‐66‐NH2‐X@SFM/Nafion composite membranes. The thermal stability, dimensional stability, mechanical properties, proton conductivity, methanol resistance, and other properties of the UiO‐66‐NH2‐X@SFM/Nafion composite membranes were subsequently comprehensively characterized. The proton conductivity of the UiO‐66‐NH2‐8@SFM/Nafion composite membrane at 80°C and 100% RH was measured to be 0.286 S cm−1, which exhibited a significant enhancement of 1.75 times compared with the original membrane. Simultaneously, the composite membrane demonstrated a remarkable reduction in methanol permeation rate. At 40°C and 100% RH, the UiO‐66‐NH2‐8@SFM/Nafion composite membrane has a selectivity of up to 20.7 × 104 S s cm−3 and a single cell density of 88.3 m W cm−2 at 60°C and 100% RH.

Multi-Substituted Phosphonated and Sulfonated Polymer Materials: Characterization and Blends with Basic Polymers

The growing demand for energy, limited resources, and climate warming call for alternative sustainable energy production. A promising candidate is the proton-exchange membrane fuel cell (PEMFC) using a proton conducting polymer as an electrolyte membrane. The most common proton-exchange membranes are based on sulfonated polymers, such as Nafion®. Since their proton conduction is driven by hydronium ions (H3O+) and hence require water, the operating temperature is limited to 100°C. Unlike in sulfonated polymer materials, the proton conduction in materials with phosphonic acid groups occurs via a hopping process and does not require water.1 This study introduces a highly substituted phosphonated and sulfonated polymer based on poly(pentafluorostyrene), which makes the material adaptable in anhydrous and hydrous operating conditions since the phosphonic acid and sulfonic acid units can conduct cooperatively. The phosphonic acid group is introduced via the nucleophilic aromatic substitution Michaelis-Arbuzov reaction. The Para-Fluoro-Thiol reaction was used to introduce sulfonic acid groups into the polymer backbone. In the past, both reaction steps were well investigated.2,3 The highly substituted polymer material was blended with a basic polymer to circumvent water solubility and investigated according to its proton conductivity, thermal stability, and mechanical properties.(1) Kumar, A. J. Mater. Chem. A 2020, 8 (43), 22632–22636. DOI: 10.1039/d0ta07732a.(2) Atanasov, V.; Oleynikov, A.; Xia, J.; Lyonnard, S.; Kerres, J. Journal of Power Sources 2017, 343, 364–372. DOI: 10.1016/j.jpowsour.2017.01.085.(3) Delaittre, G.; Barner, L. Polym. Chem. 2018, 9 (20), 2679–2684. DOI: 10.1039/c8py00287h.

Self-assembly of cis-trans Ta/W mixed-addendum POMs based on hexalacunary [H2P2W12O48]12− building blocks

The synthesis of Ta-substituted polyoxometalates has always been an attractive but challenging goal. Three novel tantalum-containing 12-tungsto-2-phosphates were successfully prepared using the water bath method. The monomer, K11Li[P2W12(TaO2)6O56]·19H2O (1), is composed of {P2W12} and 6 {Ta(O2)} building blocks, similar to [P2W12(NbO2)6O56]12−. Monomer 1 polymerized to form two cis-trans dimers, K13Li6H-cis-[P2W12Ta4(TaO2)2O59]2·61H2O (2) and KNa3Li4H12-trans-[P2W12Ta4(TaO2)2O59]2·37H2O (3). Compounds 1–3 can serve as a structural motif to manufacture additional fascinating molecular clusters, promoting the advancement of POM chemistry. In contrast to [P2W12(NbO2)6O56]12−, compound 1 exhibits exceptional stability, evidenced by ESI-MS, IR, and NMR spectroscopy. In addition, 2 and 3 exhibit high proton conductivity and superior water adsorption properties.

A pyrazine-2,3-dicarboxylic acid hybrid arsenotungstate with decent proton conduction property

A pyrazine-2,3-dicarboxylic acid hybrid arsenotungstate K5Ba5H{Ba[AsW11O37(pzdc)2]2}·22H2O (1, H2pzdc = pyrazine-2,3-dicarboxylic acid) has been synthesized. This compound displayed a dimeric polyanion which consisted of two ancient official cap-shaped [AsW11O37(pzdc)2]9– subunits linked together via a Ba2+ cation. The [AsW11O37(pzdc)2]9– subunit is fused together by a trivacant [AsW9O33]9– fragment and two {WO2(pzdc)} groups. And the [Ba(AsW9O33)2]16– subunit can be simplified into the ferrocene-like structure. What is particularly interesting is that one N and one O atom of the pzdc2– ligand can directly chelate with the W atom to construct the infrequent W–O–C–C–N five-membered ring. Compound 1 exhibits good proton conduction property with the conductivity of 1 can reach up to 2.37× 10–3 S cm-1 at 70 °C under 95% relative humidity.

Improved Proton Conductivity of Chitosan-Based Composite Proton Exchange Membrane Reinforced by Modified GO Inorganic Nanofillers.

Non-fluorinated chitosan-based proton exchange membranes (PEMs) have been attracting considerable interest due to their environmental friendliness and relatively low cost. However, low proton conductivity and poor physicochemical properties have limited their application in fuel cells. In this work, a reinforced nanofiller (sulfonated CS/GO, S-CS/GO) is accomplished, for the first time, via a facile amidation and sulfonation reaction. Novel chitosan-based composite PEMs are successfully constructed by the incorporation of the nanofiller into the chitosan matrix. Additionally, the effects of the type and amount of the nanofillers on physicochemical and electrochemical properties are further investigated. It is demonstrated that the chitosan-based composite PEMs incorporating an appropriate amount of the nanofillers (9 wt.%) exhibit good membrane-forming ability, physicochemical properties, improved proton conductivity, and low methanol permeability even under a high temperature and low humidity environment. When the incorporated amounts of S-CS/GO are 9 wt.%, the proton conductivity of the composite PEMs was up to 0.032 S/cm but methanol permeability was decreased to 1.42 × 10-7 cm2/s. Compared to a pristine CS membrane, the tensile strength of the composite membrane is improved by 98% and the methanol permeability is reduced by 51%.

New triazinephosphonate dopants for Nafion proton exchange membranes (PEM).

A new paradigm for energy is underway demanding decarbonized energy systems. Some of them rely on emerging electrochemical devices, crucial in hydrogen technologies, including fuel cells, CO2 and water electrolysers, whose applications and performances depend on key components such as their separators/ion-exchange membranes. The most studied and already commercialized Nafion membrane shows great chemical stability, but its water content limits its high proton conduction to a limited range of operating temperatures. Here, we report the synthesis of a new series of triazinephosphonate derivatives and their use as dopants in the preparation of new modified Nafion membranes. The triazinephosphonate derivatives were prepared by substitution of chlorine atoms in cyanuric chloride. Diverse conditions were used to obtain the trisubstituted (4-hydroxyphenyl)triazinephosphonate derivatives and the (4-aminophenyl)triazinephosphonate derivatives, but with these amino counterparts, only the disubstituted compounds were obtained. The new modified Nafion membranes were prepared by casting incorporation of the synthesized 1,3,5-triazinephosphonate (TPs) derivatives. The evaluation of the proton conduction properties of the new membranes and relative humidity (RH) conditions and at 60 °C, showed that they present higher proton conductivities than the prepared Nafion membrane and similar or better proton conductivities than commercial Nafion N115, in the same experimental conditions. The Nafion-doped membrane with compound TP2 with a 1.0 wt % loading showed the highest proton conductivity with 84 mS·cm-1.

A new nanocomposite membrane based on sulfonated polysulfone boron nitride for proton exchange membrane fuel cells: Its fabrication and characterization

Sulfonated polysulfone (SPSf) polymer is an alternative raw material in producing commercially used proton exchange membranes. On the other hand, hexagonal boron nitride (hBN) is one of the additives of interest for nanocomposite PEMs. In this study, nanocomposite membranes is fabricated and characterized with SPSf and hBN nanoparticles. The degree of sulfonation of the sulfonated polysulfone is determined by titration, and sulfonic acid bonds are investigated by Proton Nuclear Magnetic Resonance (1H NMR) analysis. SPSf is dissolved with dichloromethane, and hBN nanoparticles are added. After homogenizing the prepared solution with magnetic and ultrasonic stirrers, membranes are formed using Dr. Blade. 1H NMR, Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), X-Ray Diffractometer (XRD), and Thermogravimetric Analysis (TGA) analysis are examined the morphological, thermal, and organic compound structures of the membranes. Water uptake capacity, swelling ratio, proton conductivity, oxidative resistance, and mechanical properties of the membranes are determined. The highest water uptake capacity is obtained as 40.08 % in the membrane named SPSf-3 %hBN. Using hBN additive improved swelling ratio and thermal and mechanical strength properties. The proton conductivity values of polysulfone (PSf), SPSf, SPSf-1 %hBN, SPSf-2 %hBN, and SPSf-3 %hBN membranes are determined as 2.89, 6.84, 3.57, 10.8 and 5.12 mS cm−1, respectively. As a result of the analysis, it is observed that the nanocomposite membrane structure has both amorphous and crystalline homogeneous structure.