Exhibited Proton Conductivities Research Articles

Lanthanide‐Based Metal‐Organic‐Frameworks for Proton Conduction and Magnetic Properties

AbstractThe coexistence of proton conductivity and magnetic properties in metal organic frameworks (MOFs) is simply an attractive prospect to design and create multifunctional molecular materials. However, the simultaneity of interesting magnetic properties (e.g. magnetocaloric effect, slow magnetic relaxation or magnetic ordering) and proton conduction in a MOF is very implausible to be observed, as chemical and structural necessities are absolutely poles apart for either of the properties. In this context, lanthanide‐based metal‐organic frameworks (LMOFs) have emerged as an intriguing class of materials to observe such coexistence in few cases. In this perspective, the advantages of combining lanthanide ions and organic acids as ligands to construct a proton‐conductive magnetic metal organic framework are briefly discussed. The current status of this specific research area regarding some fascinating LMOFs exhibiting proton conductivity and magnetic properties is reviewed in detail. Also, a future perspective of such materials is discussed.

Effect of humidification on the grain boundary conductivity and space-charge effects in yttrium-doped barium cerate

Yttrium-doped barium cerate (BCY) exhibits proton conductivity in the nominal absence of water (pH2O ≤ 10−4 atm) below 450 °C (J. Mater. Chem. A 7 (2019) 18,135–18142). Under these conditions, the well-known instability of this material against carbon dioxide and humidity can be minimized, potentially allowing its application even in hydrocarbon-based atmospheres. Nonetheless, electrochemical transport properties of grain boundaries of BCY are still not well understood. Hence, we compare specific grain boundary conductivity and space-charge properties of BaCe0·9Y0·1O3-δ (BCY10) in both wet and low humidity by means of impedance spectroscopy in the temperature range 100–300 °C. In H2, specific grain boundary conductivity increases in nominally dry conditions, while the bulk remains practically humidity independent. Conversely, in O2, both bulk and specific grain boundary conductivities are higher in wet. The space-charge properties highlight that low levels of humidity, pH2O ~10−4 atm, are sufficient to maintain functional performance, while providing enough stability. This work offers a significant advance to the knowledge of the transport properties of this family of materials at low temperatures, with special emphasis to conditions of low humidity, for potential future applications in proton-conducting electrolyte membranes.

Long-Range Proton Transport in Films from a Reflectin-Derived Polypeptide.

Protein- and peptide-based proton conductors have been extensively studied because of their important roles in biological processes and established potential for bioelectronic device applications. However, despite much progress, the demonstration of long-range proton transport for such materials has remained relatively rare. Herein, we fabricate, electrically interrogate, and physically characterize films from a reflectin-derived polypeptide. The electrical measurements indicate that device-integrated films exhibit proton conductivities with values of ∼0.4 mS/cm and sustain proton transport over distances of ∼1 mm. The accompanying physical characterization indicates that the polypeptide possesses characteristics analogous to those of the parent protein class and furnishes insight into the relationship between the polypeptide's electrical functionality and structure in the solid state. When considered together, our findings hold significance for the continued development and engineering of not only reflectin-based materials but also other bioinspired proton conductors.

Studies on the Genesis and Proton Conductivity of Imidazole-Based Linear and Open-Framework Zinc Phosphites.

Three new zinc phosphites, [HIm]2[Zn3(HPO3)4] (1), [Zn2(HPO3)2Im2] (2), and [Zn(HPO3)Im] (3) (Im = imidazole), have been synthesized from the hydro/solvothermal reaction of zinc acetate, dimethyl phosphite, and imidazole by varying the temperature and solvent of the reaction medium. The structure of 1 is built from vertex-sharing of four HPO3-capped Zn3P3 units and adopts an open framework with 12-ring channels stabilized by HIm cations via N-H···O hydrogen bonds. For 2, the inorganic skeleton is comprised of alternating ZnO4 and HPO3 tetrahedra, while the coordinatively associated ZnN2O2 fragments occupy the 12-ring hexagonal channels. Compound 3 adopts a ladder-type one-dimensional structure and exhibits N-H···O hydrogen-bonding interactions to afford a supramolecular assembly. A plausible rationale on the genesis of 1-3 has been put forth by reacting the preformed inorganic zinc phosphites Zn{OP(O)(OMe)H}2 or [Zn2(HPO3)2(H2O)4]·H2O with imidazole as the structure-directing ligand. Alternating-current impedance measurements reveal that 1 and 3 exhibit proton conductivities on the order of 10-3-10-4 S cm-1 between 25 and 100 °C under 35 and 77% relative humidity in repeated impedance cycles (Ea = 0.22-0.35 eV). On the contrary, the conduction property is completely impaired in 2 under similar conditions.

Nanostructured Polymer Composite Electrolytes with Self-Assembled Polyoxometalate Networks for Proton Conduction

Nanostructured Polymer Composite Electrolytes with Self-Assembled Polyoxometalate Networks for Proton Conduction

Effect of sulfonic acid‐functionalized polysilsesquioxane on new semifluorinated sulfonated polytriazole composites and investigation of proton exchange membrane properties

AbstractA new semifluorinated sulfonated copolytriazole is synthesized, maintaining a particular degree of sulfonation of 80% following the click reaction of two terminal azides 1,4‐bis‐[{2′‐trifluromethyl 4′‐(4″‐azidophenyl)phenoxy}]phenyl, and 4,4′‐diazido‐2,2′‐stilbenedisulfonic acid disodium salt with equal molar amounts of two dialkyne monomers namely, 1,3‐diethynylbenzene and 3,5‐bis(prop‐2‐ynyloxy)benzoic acid and designated as PTEHCSH‐80. Further, the copolytriazole is used to prepare polymer composites employing the sol‐gel reaction of the starting precursor sol 3‐(trihydroxylsilyl) propane‐1‐sulfonic acid. The weight percentage (wt%) of the filler is varied from 0 to 10 wt%, and a series of polymer composite films are prepared and abbreviated as PTEHCSH‐80/X (where X is wt% of the filler, X = 0. 2.5, 5.0, 7.5, 10.0). All the polymer composites are characterized through FTIR spectroscopic techniques. The composite films revealed various desirable properties such as high thermochemical and dimensional and mechanical stabilities in their corresponding acid form. Moreover, the composites exhibited proton conductivities ranging from 62 to 98, 117 to 182, and 131 to 195 mS/cm at three different temperatures 30°C, 80°C, and 90°C, respectively, in a hydrated state.

Synthesis of 2,2′-hindered pyridine containing semifluorinated polytriazoles and investigation for low-temperature proton exchange membrane application with enhanced oxidative stability

A series of new sulfonated copolytriazoles were prepared from a novel fluorinated diazide monomer with pyridine moiety to enhance both the oxidative stability and proton conductivity of proton exchange membranes. These proton donor–acceptor based copolymers and homopolymers were synthesized by click cycloaddition polymerization of the dialkyne monomer 1,2,4,5-tetrafluoro-3,6-bis(prop-2-yn-1-yloxy)benzene (TFAK) with or without the pyridine containing diazide monomer 2,2′-bis(4-(4-azidophenoxy)-3-(trifluoromethyl)phenyl)pyridine (PYFAZ) and the sulfonated diazide monomer 4,4′-diazido-2,2′-stilbenedisulfonic acid disodium salt (DSSAZ). 1H, 13C, and 19F NMR, in addition to FTIR analyses, confirm the formation of polytriazoles with a graded degree of sulfonation between 70% and 100%. The solution cast membranes were flexible and showed high chemical, thermal and mechanical properties. Inclusion of pyridine moiety proved to play a significant role in increasing peroxide stability by quenching hydroxyl and hydroperoxide radicals and forming pyridine-N-oxide, which was analyzed by EPR and FTIR spectroscopy. The presence of pyridine moiety also enhanced proton conductivity owing to the presence of the weakly basic nitrogen in pyridine that acts as a proton hopping site. AFM and HR-TEM images of the membranes indicated the formation of phase-separated morphology and that became more pronounced with the increase in the degree of sulfonation. The membranes obtained from PYFTSH-90 copolymer exhibited proton conductivity of 125 mS cm−1 at 80 °C, which is comparable to Nafion-117. The proton conductivity of PYFTSH-90 was further increased to 139 mS cm−1 at 90 °C. Thus, three significant objectives have been fulfilled in this work, namely (i) high proton conductivity, (ii) high hydrolytic stability, and (iii) high peroxide stability. These properties demonstrate that these copolymer membranes are potentially highly suitable for application in low-temperature proton exchange membrane fuel cell (PEMFC).

Construction of Strandberg‐Type Polyoxometalate‐Based Inorganic‐Organic Hybrid Material with Water‐Assisted Proton Conductivity

AbstractPolyoxometalates (POMs) were widely applied in the field of proton conduction due to their rapid charge transfer capability and large proton capacity. The Strandberg‐type POM has small size and large charge density, can form functional organometallic compounds with metal ions. In this study, by using [P2Mo5O23]6− coordinate with the cobalt ion with cytosine as the structure‐directing agent, a compound of Co1.5(C4H6N3O)3[P2Mo5O23]⋅8.5H2O was synthesized, which showed one‐dimensional chain structure and exhibits proton conductivity of 3.62 × 10−4 S cm−1 at 98 °C and 97% RH. The amino group and nitrogen atoms in the cytosine can form hydrogen bond with the coordination water molecules. Meanwhile, the hydrogen bond network can also be formed between the water molecules, which is one of the main factors for proton conduction performance. The compound Co1.5(C4H6N3O)3[P2Mo5O23]⋅8.5H2O exhibited the corresponding activation energies and conduction mechanisms at different temperature intervals, by analyzing the temperature‐dependent PXRD spectrum under high‐humidity conditions, which showed the hydrogen bond network of the crystal during the temperature changes affects its proton conduction performance.

Thermal stability and proton conductivity of densely proton injected phosphate glasses containing rare-earth elements

• Effects of rare-earth element species in proton conducting phosphate glasses were studied. • Tg and glass structures were almost identical irrespective of the rare-earth element species. • Thermal stability was found to be significantly dependent on the rare-earth element species. • Surprisingly, the glass containing dy was stable up to 600 °C. • The glass containing dy exhibited proton conductivity of 4 × 10 −3 Scm −1 at 550 °C. Sodium ions in 25NaO 1/2 –3MgO–7 Ln O 3/2 –3GeO 2 –62PO 5/2 (mol%, Ln = La, Nd, Gd, Dy, Y, Yb) glasses were electrochemically substituted with protons with a substitution rate higher than 90% by using an Alkali-Proton Substitution (APS) technique.. Effects of rare-earth element species on various properties were investigated, such as the glass transition temperature (Tg), structure, thermal stability, and proton conductivity. Whereas Tg and glass network structures were almost mutually identical irrespective of the rare-earth element species, their thermal stability as evaluated from the onset temperature of weight loss during heating was found to be significantly dependent on the rare-earth element species. The glass containing Dy after APS exhibited the highest thermal stability among the glasses: it was stable up to 600 °C, which is ca. 370 °C higher than its Tg, without crystallization. Thermal stability depending on the rare-earth element species was related to the difference in the structure between the glass and the crystalline phase that precipitated from the glass. The proton conductivity was almost independent of the rare-earth element species. Therefore, the glass containing Dy which exhibited the highest thermal stability among the glasses exhibited the highest proton conductivity of 4 × 10 −3 Scm −1 at 550 °C.

Hybrid organic-inorganic materials on the basis of acrylic monomers and TEOS prepared by simultaneous UV-curing and sol-gel process

In this work cross-linked hybrid organic-inorganic membranes consisting of polymeric matrix functionalized with sulfonic groups and uniformly distributed silica domains have been successfully synthesized through in situ polymerization strategy via photo-initiated copolymerization of acrylic monomers (acrylonitrile AN, acrylamide AAm, 3-sulfopropyl acrylate potassium salt SPAK) and simultaneous formation of silica counterpart using TEOS-based sol-gel system. N,N′-methylenebis(acrylamide) (MBA) was used as a cross-linker. The ratio between monomers was maintained stable, whereas the amount of added sol-gel system was varied. The influence of inorganic component content on properties of hybrid polymer-inorganic membranes was investigated. Chemical composition, thermal properties, structure and morphology of the obtained hybrid membranes were investigated by ATR-FTIR, TGA, DSC, SEM and EFTEM. Proton conductivity of the synthesized membranes was high (7.6 to 13.5 mS/cm) and increases with an increase of silica content. The prepared membranes were thermally stable up to 90 °C, and exhibited proton conductivity and swelling coefficients sufficient for possible use as proton-conducting membranes.

Nano-ordered aromatic/alicyclic polybenzimidazole blend membranes

In the present work, polybenzimidazole (PBI) containing aliphatic (cyclohexane based, ARB-0, I.V. = 1.5 dL/g) and aromatic (terephthalic acid based, ARB-100, I.V. = 3.46 dL/g) backbones were synthesized. On blending the two polymers, PBIs with tunable mechanical and proton conductivity were achieved. ARB-0 exhibited proton conductivity of 114 mS/cm whereas ARB-100 marked a high value of 220 mS/cm at 160 °C. ARB-100 resulted in high tensile modulus of 11 GPa meanwhile ARB-0 exhibited 2 GPa only. The corresponding elongations were 2 and 27% respectively. The aliphatic-aromatic blends resulted in good elongation, modulus and conductivity. The aromatic rich blend composition (ARB-67) displayed maximum proton conductivity (240 mS/cm) and morphology exhibited local ordering behavior due to aliphatic-aromatic intra-chain interactions.

Polybenzimidazole as proton conducting filler in polydimethylsiloxane: Enhanced oxidative stability and membrane properties

ABSTRACTIn this work, pyridine‐based low‐molecular‐weight polybenzimidazole (LMP) was synthesized (inherent viscosity: 0.52 dL g−1) by controlling the reaction time. The synthesized LMP was incorporated into polydimethylsiloxane (PDMS) matrix to impart proton conductivity. The composite membrane containing 30 wt % of LMP exhibited proton conductivity of 16 mS cm−1 at 100–120 °C. The LMP chains were bundled and formed clusters (aggregates) in the PDMS matrix as observed in field emission scanning electron microscopy. This is attributed to nonpolar (siloxane)–polar (polybenzimidazole) repulsion. An impressive weight loss of 8.6% was observed after 120 h Fenton's test that indicates the high oxidative stability of composite membranes. However, elongation of composite membranes was decreased compared to that of pristine PDMS, which is attributed to the incorporation of rigid LMP chains. The resultant composite membranes exhibited moderate proton conductivity, low moisture absorption, and good thermal stability. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48151.

Synthesis, Characterization and Performance Evaluation of Hybrid Multiblock Copolymers for Proton Exchange Membrane Fuel Cells

Present research has been conducted for a new series of multiblock copolymers based on hydrophobic oligomer poly (arylene ether sulfone) containing 6F-bisphenol A and hydrophilic oligomer sulfonated poly (arylene ether ketone) containing pendant carboxylic acid group with varying hydrophobic block length. The ionic liquid is embedded into the synthesized multiblock copolymers to fabricate the hybrid multiblock membranes via solution casting method. The copolymers are characterized by 1H NMR, FT-IR and gel permeation chromatography (GPC) techniques. The thermal stability of the membranes has been investigated through thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) thermograms. The ionic synergism between the I.L and the acidic groups present in the multiblock copolymer provides a free pathway for the protons to travel and the resulting hybrid membranes exhibit proton conductivity in the range of (0.03 - 0.16) S/cm at 80 °C. Compared with pristine membranes, the hybrid membranes exhibit improved oxidative and mechanical stability. Moreover, the scanning electron microscopy (SEM) investigation depicts better phase separation in hybrid membranes than pristine membranes by forming ionic clusters. The membranes have been tested in H2/O2 fuel cell and their performance is compared with the state-of-art Nafion 117 membrane. For hybrid membranes, with the addition of I.L, the voltage and power densities values increased up to 0.59 V and 0.23 Wcm-2, respectively. These investigations suggest that the synthesized multiblock membranes are promising candidate for proton exchange membrane fuel cells.

Role of acetyl group on proton conductivity in chitin system

Measurements of proton conductivity in chitin and chitosan have been carried out and proton conductivity is investigated. From the measurement of fuel cell based on the deacetylated chitin (chitosan) electrolyte, it was found that chitosan becomes the electrolyte of fuel cell. This result indicates that chitosan in humidified condition exhibits proton conductivity as seen in chitin. Moreover, proton conductivity in chitin is about 100 times higher than that in chitosan. These results indicate that acetyl group is an important factor for the appearance of higher proton conductivity in chitin system. In addition, the anisotropy of proton conductivity in chitosan is much larger than that in the orientated chitin. Considering that proton conductivity is caused by proton transfer in water bridges, these results indicate that chitin and chitosan possess quasi-three dimensional water bridges and quasi-two dimensional water bridges, respectively. It is deduced from these results that acetyl group is a key factor not only the appearance of higher proton conductivity but also the realization of quasi-three dimensional proton conductivity.

Understanding the effect of Ce and Zr on chemical expansion in yttrium doped strontium cerate and zirconate by high temperature X-ray analysis and density functional theory

Aliovalent cation-doped perovskite-type oxides (ABO3) exhibit proton conductivity originating from the hydration of oxide ion vacancies, which is accompanied by structural deformation, i.e. chemical expansion. The chemical expansion may lead to failure in electrochemical devices, and thus it is necessary to understand the causes of this process at the atomic scale. In this study, the chemical expansion behaviors of Y-doped strontium cerate and zirconate were comparatively investigated. High-temperature X-ray diffraction (HT-XRD) and thermogravimetric analysis (TGA) revealed that the cerate exhibits larger chemical expansion. Density Functional Theory (DFT) calculations revealed that this tendency can be accounted for by the different atomic distribution of the Y dopant between the cerate and zirconate, which results in differences in the size of the oxide ion vacancies to be hydrated as well as different elastic character.

Non-molecular monovalent metal organophosphonates and diphosphonates

The solid state chemistry of non-molecular monovalent metal organophosphonates and diphosphonates is relatively new and evolving research arena. The syntheses and structural characterization of about fifty such compounds are reported in the literature. They are a variety of mono- and di-phosphonates of inorganic monovalent cations, namely, alkali metal, thallium, cuprous, silver and mercurous ions and also ammonium ions. They have x:2 (x = 1–4) ratios of metal to phosphonate moieties and possess mostly layered and pillared-layered structures. Some of them function as solid Brönsted acids and exhibit proton conductivity.

Sulfophenylated Terphenylene Copolymer Membranes and Ionomers.

The copolymerization of a prefunctionalized, tetrasulfonated oligophenylene monomer was investigated. The corresponding physical and electrochemical properties of the polymers were tuned by varying the ratio of hydrophobic to hydrophilic units within the polymers. Membranes prepared from these polymers possessed ion exchange capacities ranging from 1.86 to 3.50 meq g-1 and exhibited proton conductivities of up to 338 mS cm-1 (80 °C, 95 % relative humidity). Small-angle X-ray scattering and small-angle neutron scattering were used to elucidate the effect of the monomer ratios on the polymer morphology. The utility of these materials as low gas crossover, highly conductive membranes was demonstrated in fuel cell devices. Gas crossover currents through the membranes of as low as 4 % (0.16±0.03 mA cm-2 ) for a perfluorosulfonic acid reference membrane were demonstrated. As ionomers in the catalyst layer, the copolymers yielded highly active porous electrodes and overcame kinetic losses typically observed for hydrocarbon-based catalyst layers. Fully hydrocarbon, nonfluorous, solid polymer electrolyte fuel cells are demonstrated with peak power densities of 770 mW cm-2 with oxygen and 456 mW cm-2 with air.

A Multifunctional Lanthanide Carbonate Cluster Based Metal-Organic Framework Exhibits High Proton Transport and Magnetic Entropy Change.

A novel multifunctional, three-dimensional (3D) lanthanide carbonate cluster based metal-organic framework (MOF) with the general formula {[Gd2(CO3)(ox)2(H2O)2]·3H2O} n (1) has been synthesized via self-assembly of gadolinium (Gd) carbonate and oxalate under hydrothermal conditions. Single-crystal X-ray diffraction reveals that the compound 1 consists of the Gd carbonate cluster with oxalic acid ligands, which form a 3D framework structure with an ordered one-dimensional (1D) pore channel along the a-axis. The coordination water molecules of Gd3+ ions point to the interior of the pore and form a 1D hydrogen bond pathway with oxygen atoms in adjacent oxalic acid that is stable at high temperature (up to 150 °C). The compound 1 features multiple hydrogen-bonding walls and good thermal stabilities, and shows the highest proton conductivity of 1.98 × 10-3 S cm-1 at T = 150 °C and in room air without additional humidity. Magnetic investigations of compound 1 demonstrate that weak antiferromagnetic couplings between adjacent Gd3+ ions bring about large cryogenic magnetocaloric effects. Remarkably, the maximum entropy change (-Δ Sm) of compound 1 reaches 58.5 J kg-1 K-1 at 2 K for a moderate field change (Δ H = 7 T). Moreover, the isomorphous MOFs: {[Ln2(CO3)(ox)2(H2O)2]·3H2O} n (Ln3+ = Ce3+(2), Pr3+(3), Nd3+(4), Tb3+(5)) also are structurally and functionally characterized, and compounds 2-5 exhibit proton conductivity above 10-3 S cm-1 in room air and without additional humidity.

Eco-friendly cellulose based solid electrolyte with high performance and enhanced low humidity performance by hybridizing with aluminum fumarate MOF

Abundant yet undeveloped, cellulose and various derivatives of cellulose are materials that we see and touch every day. Here, we report a novel polymer proton conducting electrolyte synthesized by chemical modification of hydroxypropyl cellulose, which opens a new possibility of utilizing a renowned environmental friendly material for environmentally friendly applications. The modified cellulose by attaching sulfonic acid functional groups exhibits proton conductivity of 172 mS/cm at room temperature under 100% relative humidity with negligible electron or hole leakage through the membrane. By hybridizing the modified cellulose with aluminum fumarate metal-organic-framework (A520), dehydration of the cellulose based electrolyte membrane is significantly moderated to enhance low humidity conductivity by more than an order of magnitude. The A520 hybridized sulfonated cellulose is utilized as the electrolyte for all-solid-state supercapacitor, which demonstrated specific capacitance as high as 135.14 F/g at 75% relative humidity with stable performance even at low humidity.

Characterization and fuel cell performance of divinylbenzene crosslinked phosphoric acid doped membranes based on 4-vinylpyridine grafting onto poly(ethylene-co-tetrafluoroethylene) films

The effect of divinylbenzene (DVB) as crosslinker on the graft polymerization of 4-vinylpyridine (4VP) from poly(ethylene-co-tetrafluoroethylene) (ETFE) films was studied. The resulted films were doped with phosphoric acid (PA) and characterized for mechanical, surface, thermal properties, and fuel cell performance. The crosslinked membrane obtained from grafting a mixture of 4VP with 1% DVB improved the polymerization kinetics and resulted in about 50% graft level depending on graft conditions. The crosslinked membranes were also found to have better mechanical properties compared to its noncrosslinked counterpart. The resulted membrane exhibited proton conductivity as high as 75 mS/cm under 50% relative humidity (RH) at 120 °C, besides almost doubling the power output of fuel cell compared to a noncrosslinked membrane. To the best of our knowledge, DVB crosslinked 4VP based ETFE membranes were, for the first time, tested in practical fuel cell test station correlating their performance to operating temperature. Furthermore, surface properties of produced membranes were additionally correlated to the degree of crosslinking. Humidity dependence is less pronounced in the produced membranes resulting in strong potential for testing at intermediate temperature (80–120 °C) polymer electrolyte membrane fuel cells.