Temperature Dependence Of Proton Conductivity Research Articles

Origin of the Temperature Dependence of Proton Conductivity in Phosphate Glass Prepared by Alkali-Proton Substitution Technique

The temperature dependence of proton conductivity in 36HO1/2−4NbO5/2−2BaO-4LaO3/2−4GeO2−1BO3/2−49PO5/2 glasses prepared through the alkali-proton substitution method was investigated in this study. The activation energy of proton conduction, E a , was found to exhibit an non-Arrhenius type temperature dependence. The origin of the temperature dependence of the proton conductivity caused by thermal expansion of the glass structure was discussed in terms of the effect of changes in the local environment surrounding the protons. These changes were elucidated using Raman spectroscopy, 1H- and 31P-NMR, infrared spectroscopy, and molecular modeling. Because protons form O-H bonds, they are sensitive to changes in the distance between two oxygen atoms, which affects the strength of the hydrogen bond, and concluded that there is a temperature dependence as observed.

Proton-conducting Organic-inorganic Sulfo-containing Membranes for Fuel Cell

Cross-linked organiс-inorganic sulfo-containing membranes of various compositions based on acrylic monomers (acrylonitrile, acrylic acid, 3-sulfopropylacrylate potassium salt, ethylene glycol diacrylate) and sol-gel systems of tetraethoxysilane have been developed. Synthesis of the polymer matrix was carried out by UV-initiated polymerization of the monomer mixture and the inorganic component was formed in situ while conducting the sol-gel process of the precursor. FTIR, SEM, EDS, DMA, impedance spectroscopy were used to characterize the synthesized materials. The influence of inorganic component content on the properties of the membranes was investigated. DMA results show that an increase in silica content leads to a decrease in packing density and an increase in structural heterogeneity in sulfo-containing polyacrylate/silica membranes. The highest values of proton conductivity 1.12 ꞏ 10−2 Sm/cm at 60 °C were found in membranes containing 3 wt.%. of the added sol-gel system. Further increase of silica content does not increase the proton conductivity of the membranes. The proton transfer activation energies in the membranes were calculated from the temperature dependence of proton conductivity. The obtained cross-linked sulfo-containing organic-inorganic materials can be used for the development of proton-conducting membranes for fuel cells.

Magnetic aligned sulfonated carbon nanotube/Nafion composite membranes with anisotropic mechanical and proton conductive properties

Nafion composite membranes with various amounts of sulfonated multi-walled carbon nanotubes (Su-CNTs) were prepared either in or without a strong magnetic field. Interestingly, it is found that being recast in a strong magnetic field, the tensile strength at break and proton conductivity of Su-CNTs/Nafion composite membranes parallel to the magnetic field direction were higher than those perpendicular to magnetic field. Remarkably, such anisotropic mechanical property and proton conductivity of Su-CNTs/Nafion composite membranes strongly depend on water uptake and temperature, in particular the content of Su-CNTs. Quite a different dependence of the proton conductivity of the composite membranes on Su-CNT content, relative humidities and temperatures is well explained for the anisotropic proton conductivity of the Su-CNTs/Nafion membrane recast in a strong magnetic field, which is attributed to the preferential proton transporting along ionic water channels mainly coalesced by the orientated Su-CNTs at a specific water uptake. For Nafion composite membranes with 5 wt.% Su-CNTs, the proton conductivity along the direction of treating magnetic field approaches to 0.216 S/cm, which is $$\sim$$ 46% higher than that perpendicular to the magnetic field at 95 $$^{\circ }$$ C. The present work provides a deep insight of the humidity and temperature dependence of proton conductivity of Su-CNTs/Nafion composite membranes and a new strategy for fabrication proton exchange membranes with high proton conductivity as well as good mechanical property.

New phase transition in superprotonic phase of inorganic solid acid Cs2(HSO4)(H2PO4)

The crystal structure, the thermal analysis and the proton conduction in the superprotonic phase of Cs2(HSO4)(H2PO4) have been investigated from 113K to 423K. A new structure model has been proposed in terms of the temperature change of XRD patterns. A phase transition was found in the superprotonic phase on the basis of the XRD and the thermal analysis in the low-temperature region. The phase transition shows a glass-transition-like behavior. The temperature dependence of proton conductivity has been discussed in relation to this transition.

Proton exchange membrane fuel cell of polybenzimidazole electrolyte doped with phosphoric acid and antimony chloride

Abstract The proton conductivity of phosphoric acid (PA) doped polybenzimidazole (PBI) membrane is improved through imbibing antimony pentachloride before doping PA. The antimony involvement diminishes the temperature dependence of proton conductivity in the targeted temperature range 160–260 °C. Among the compositions being prepared, the most conductive one exhibits 8.08 × 10−2 S cm−1 at 180 °C, with a small temperature sensitivity 6.3 × 10−5 S cm−1 °C−1. Several membrane-electrode assemblies (MEAs) have been prepared with the Pt/C catalyst layers to evaluate the practicality of co-doped PBI membrane. After proper activation, the hydrogen/air cell generates substantial electric power, denoted by its peak value over 500 mW cm−2 at 180 °C. Impedance analysis indicates carbon monoxide poisoning affects overall MEA kinetics, as evidenced in the rising resistances of electrolyte, cathode, and anode. But the poisoned performance due to 3% CO/H2 fuel can be rejuvenated after the fuel is switched back to pure hydrogen in one or two hours.

Proton Conductivity in Doped Aluminum Phosphonate Sponges

Proton-conducting networks (NETs) were prepared successfully by the insertion of phosphonated nanochannels into organic-inorganic hybrid materials that contain Al(3+) as the connector and hexakis(p-phosphonatophenyl)benzene (HPB) as the linker. Noncomplexed phosphonic acid groups remain in the framework, which depends on the ratio of both compounds, to yield a proton conductivity in the region of 10(-3) S cm(-1). This conductivity can be further improved and values as high as Nafion, a benchmark proton-exchange membrane for fuel cell applications, can be obtained by filling the network pores with intrinsic proton conductors. As a result of their sponge-like morphology, aluminum phosphonates adsorb conductive small molecules such as phosphonic acids, which results in a very high proton conductivity of approximately 5 × 10(-2) S cm(-1) at 120 °C and 50 % relative humidity (RH). Contrary to Nafion, the doped networks show a remarkably low temperature dependence of proton conductivity from external humidification. This effect indicates a transport mechanism that is different to the water vehicle mechanism. Furthermore, the materials exhibit an activation energy of 40 kJ mol(-1) at 15 % RH that starts to diminish to 10 kJ mol(-1) at 80 % RH, which is even smaller than the corresponding values obtained for Nafion 117.

Proton Transport Pathways in an Acid–Base Complex Consisting of a Phosphonic Acid Group and a 1,2,3-Triazolyl Group

The proton transport pathways in an acid-base complex consisting of a phosphonic acid group and a 1,2,3-triazolyl group were studied using density functional theory (DFT) calculations in terms of stable configurations and transition states of the molecular or ionic dimers and trimers and verified by proof-of-concept experiments including experimental measurements of overall conductivity and (1)H NMR and FTIR spectroscopy of the methylphosphonic acid (MPA) and 1,2,3-triazole (Tri) complex as well as overall proton conductivity of polymeric blend of poly(vinylphosphonic acid) (PVPA) and poly(4-vinyl-1H-1,2,3-triazole) (PVTri). From the DFT calculations of dimers and trimers composed of ethylphosphonic acid (EPA), Tri, and their deprotonated counterparts, it was concluded that the intermolecular hydrogen bonds of the transition states corresponding to proton transport are much shorter than those of stable configurations, but the O-H and N-H bonds are much longer than those of stable configurations. The tautomerization activation energy decreases from 0.927-1.176 eV in Tri-Tri dimers to 0.336-0.444 eV in the EPA-Tri dimers. From the proof-of-concept experiments, about a 50 fold increase in overall conductivity was observed in the MPA-Tri complex consisting of 10% (molar ratio) MPA compared to pure Tri, and the calculated activation energy is consistent with the experimental activation energy evaluated from temperature dependence of proton conductivity of pure Tri and the MPA-Tri complex. In addition, the fast proton exchange between MPA and Tri, consistent with the DFT calculations, was verified by (1)H NMR and FTIR spectroscopy. Finally, a polymeric blend of PVPA and PVTri was prepared, and its proton conductivity at about 2.1 mS·cm(-1) in anhydrous state at 100 °C was observed to be significantly higher than that of PVPA or of poly(VPA-co-1-vinyl-1,2,4-triazole). The proton conductivity of the polymeric PVPA and PVTri blend in humidity state is in the same range as that of NAFION 117.

Molecular dynamics in (NH4)3H(SeO4)2 at superionic phase transitions: Raman spectroscopy study

This article presents detailed temperature Raman spectra changes at two superprotonic phase transitions of (NH4)3H(SeO4)2. The study of temperature evolution of Raman spectra has shown great changes at low temperature phase transitions at T 3 and T 4, whereas only very small changes have been observed at the two superionic transformations at T 1S and T 2S. The stretching vibration frequencies of proton donor and acceptor selenate tetrahedra have been found to change slightly in the temperature range 295–341 K with a slope change at T 1S and T 2S. A slope change in temperature dependence of proton conductivity has also been observed at the same temperatures.

Proton Conducting Membranes Based on Poly(2,2′‐imidazole‐5,5′‐bibenzimidazole)

AbstractPoly(2,2′‐imidazole‐5,5′‐bibenzimidazole) (PBI‐imi) was synthesized via the polycondensation between 3,3′,4,4′‐tetraaminobiphenyl and 4,5‐imidazole‐dicarboxylic acid. Effects of the reaction conditions on the intrinsic viscosity of the synthesized polymers were studied. The results show that the molecular weight of the polymers increases with increasing monomer concentration and reaction time, and then levels off. With higher reaction temperature, the molecular weight of the polymer is higher. With the additional imidazole group in the backbone, PBI‐imi shows improved phosphoric acid doping ability, as well as a little higher proton conductivity when compared with widely used poly[2,2′‐(m‐phenylene)‐5,5′‐bibenzimidazole] (PBI‐ph).Whereas, PBI‐imi and PBI‐ph have the similar chemical oxidation stability. PBI‐imi/3.0 H3PO4 composite membranes exhibit a proton conductivity as high as 10–4 S cm–1 at 150 °C under anhydrous condition. The temperature dependence of proton conductivity of acid doped PBI‐imi can be modeled by an Arrhenius equation.

H 3PO 4-doped 1,2,4-triazole-polysiloxane proton conducting membrane prepared by sol–gel method

The development of anhydrous proton exchange membrane is critical for the polymer electrolyte membrane fuel cell (PEMFC) operating at intermediate temperature (100–200 °C). In the present work, H 3PO 4-doped 1,2,4-triazole-polysiloxane proton conducting membrane is successfully prepared by sol–gel reaction. The molecular structure of the PGA-xH 3PO 4 is confirmed via Fourier-transform infrared spectroscopy (FTIR). Thermogravimetry (TG) analysis shows that the samples were thermally stable up to approximately 250 °C. The fracture surface morphology of the materials is characterized by scanning electron microscopy (SEM). The temperature dependence of proton conductivity of all the membranes exhibits an Arrhenius behavior. The proton conductivities of these membranes increase with dopant concentration and the temperature. In an anhydrous state, the proton conductivity of PGA-1H 3PO 4, PGA-2H 3PO 4 and PGA-3H 3PO 4 is 1.48 × 10 − 3 , 1.07 × 10 − 2 ,1.43 × 10 − 2 S cm − 1 at 200 °C, respectively. According to FTIR results, the added H 3PO 4 is presumed to break up the hydrogen-bonding network of pure PGA, facilitating ring-reorientation and thus Grotthus mechanism proton transport. In PGA-2H 3PO 4, the extra H 3PO 4 may act as a bridge providing effective proton conduction. Therefore the proton conductivity of PGA-2H 3PO 4 is greatly improved compared with PGA-1H 3PO 4.

Synthesis and properties of poly[2,2′-(4,4′-(2,6-bis(phenoxy) benzonitrile))-5,5′-bibenzimidazole] for proton conducting membranes in fuel cells

Poly[2,2′-(4,4′-(2,6-bis(phenoxy) benzonitrile))-5,5′-bibenzimidazole] (PBI-CN) was synthesized via the polycondensation of 3,3′,4,4′-tetraaminobiphenyl and 2,6-bis(4-carboxyphenoxy) benzonitrile. The introduction of the nitrile group to the main chain of PBI-CN can provide both strong polarity and a reactive site for further reaction. The effects of different reaction conditions on the intrinsic viscosity of the synthesized polymer are discussed, which is consistent with the regular pattern. After appropriate purification of starting materials and optimization of polymerization conditions, the synthesized polymer can exhibit higher intrinsic viscosity, which means higher molecular weight. The solubility, chemical oxidation stability, thermal degradation behavior, acid doping ability, and proton conductivity of the synthesized polymers were studied. Compared with poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] (PBI-ph), the introduction of –C≡N and –O– group in PBI-CN provides the polymer with better acid doping ability and chemical oxidation stability, while the solubility and thermal stability decrease a little. The proton conductivity of PBI-CN/3.5H3PO4 composite membranes can reach ∼10−3 S cm−1 at 170 °C under anhydrous condition. The temperature dependence of proton conductivity of the acid doped membranes can be modeled by an Arrhenius relation.

Preparation and Characterisation of Proton Exchange Membranes Based on Crosslinked Polybenzimidazole and Phosphoric Acid

AbstractCrosslinked polybenzimidazole (PBI) was synthesised via free radical polymerisation between N‐vinylimidazole and vinylbenzyl substituted PBI. The degree of crosslinking increases with increasing content of the crosslinker. The phosphoric acid doping behaviour, mechanical properties, proton conductivity and acid migration stability of crosslinked PBI and linear PBI are discussed. The results show that the acid doping ability decreases with increasing degree of crosslinking of PBI. The introduction of N‐vinylimidazole in PBI is beneficial to its oxidation stability. The mechanical stability of crosslinked PBI/H3PO4 membrane is better than that of linear PBI/H3PO4 membrane. The proton conductivity of the acid doped membranes can reach ∼10–4 S cm–1 for crosslinked PBI/H3PO4 composite membranes at 150 °C. The temperature dependence of proton conductivity of the acid doped membranes can be modelled by an Arrhenius relation. The proton conductivity of crosslinked PBI/H3PO4 composite membranes is a little lower than that of linear PBI/H3PO4 membranes with the same acid content. However, the migration stability of H3PO4 in crosslinked PBI/H3PO4 membranes is improved compared with that of linear PBI/H3PO4 membranes.

Mechanisms of proton conduction and gating in influenza M2 proton channels from solid-state NMR.

The M2 protein of influenza viruses forms an acid-activated tetrameric proton channel. We used solid-state nuclear magnetic resonance spectroscopy to determine the structure and functional dynamics of the pH-sensing and proton-selective histidine-37 in M2 bound to a cholesterol-containing virus-envelope-mimetic membrane so as to better understand the proton conduction mechanism. In the high-pH closed state, the four histidines form an edge-face π-stacked structure, preventing the formation of a hydrogen-bonded water chain to conduct protons. In the low-pH conducting state, the imidazoliums hydrogen-bond extensively with water and undergo microsecond ring reorientations with an energy barrier greater than 59 kilojoules per mole. This barrier is consistent with the temperature dependence of proton conductivity, suggesting that histidine-37 dynamically shuttles protons into the virion. We propose a proton conduction mechanism in which ring-flip-assisted imidazole deprotonation is the rate-limiting step.

Poly(vinyl alcohol)/sulfated β-cyclodextrin for direct methanol fuel cell applications

We report a composite membrane based on poly(vinyl alcohol) and sulfated β-cyclodextrin in this paper. TGA and SEM tests provide direct evidence of the thermal stability and the uniform structure of the composite membranes. The performances of the composite membranes are investigated in terms of swelling behavior, methanol permeability and proton conductivity as function of sulfated β-cyclodextrin content. We find that the introduction of sulfated β-cyclodextrin can reduce water uptake. The temperature dependence of proton conductivity reveals that the proton conducting activation energy of the composite membranes is similar to that of Nafion 115, in other words, both the vehicle and Grotthus mechanisms are assumed to be responsible for the composite membranes’ proton transfer. Methanol permeability decreases as the methanol feed concentration increases from 2 M to 20 M. Both proton conductivity and methanol permeability increases with increasing sulfated β-cyclodextrin. The selectivity of the composite membranes defined as the ratio of proton conductivity to methanol permeability obtains the maximum of 1.710 × 104 S s cm−3 at the composition of 17 wt.% sulfated β-cyclodextrin. The MEAs fabricate with these membranes are tested, no distinct change occurred to the composite membranes after the MEAs operating for 288 h. These data indicates the chemical and electrochemical stability of the membranes and their potential application in direct methanol fuel cells.

Synthesis and properties of novel sulfonated (co)polyimides bearing sulfonated aromatic pendant groups for PEFC applications

AbstractNovel sulfonated diamines bearing aromatic pendant groups, namely, 3,5‐diamino‐3′‐sulfo‐4′‐(4‐sulfophenoxy) benzophenone (DASSPB) and 3,5‐diamino‐3′‐sulfo‐4′‐(2,4‐disulfophenoxy) benzophenone (DASDSPB), were successfully synthesized. Novel side‐chain‐type sulfonated (co)polyimides (SPIs) were synthesized from these two diamines, 1,4,5,8‐naphthalene tetracarboxylic dianhydride (NTDA) and nonsulfonated diamines such as 4,4′‐bis(3‐aminophenoxy) phenyl sulfone (BAPPS). Tough and transparent membranes of SPIs with ion exchange capacity of 1.5–2.9 meq g−1 were prepared. They showed good solubility and high thermal stability up to 300 °C. They showed isotropic membrane swelling in water, which was different from the main‐chain‐type and sulfoalkoxy‐based side‐chain‐type SPIs. The relative humidity (RH) and temperature dependence of proton conductivity were examined. At low RH, the novel SPI membranes showed much higher conductivity than the sulfoalkoxy‐based SPIs. They showed comparable or even higher proton conductivity than Nafion 112 in water at 60 °C (>0.10 S cm−1). The membrane of NTDA‐DASDSPB/BAPPS (1/1)‐s displayed reasonably high proton conductivities of 0.05 and 0.30 S cm−1 at 50 and 100% RH, respectively, at 120 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2862–2872, 2006

Proton Conductivity of Acid Doped Styrene‐Maleic Imide Copolymer With Benzimidazole Side Group

AbstractSummary: Styrene‐maleic imide copolymer with benzimidazole side group was prepared from 2‐amino‐benzimidazole and styrene‐maleic anhydride copolymer. The structures of the new styrene‐maleic imide copolymers from both random and alternating styrene‐maleic anhydride copolymer were characterized by FTIR, DSC, and gel permeation chromatography (GPC). Styrene‐maleic imide copolymer has good solubility, excellent film forming ability, and is easy to prepare, though the solubility of styrene‐maleic imide copolymer decreases a little with increasing maleic imide. The proton conductivity of phosphoric acid doped styrene‐maleic imide copolymer was studied. The temperature dependence of proton conductivity in H3PO4 doped a‐styrene‐maleic imide copolymer can be fitted by a simple Arrhenius equation very well, while H3PO4 doped r‐styrene‐maleic imide copolymer has somewhat deviation from Arrhenius equation. The structure of alternating copolymer is more favorable for proton transport contributed by hopping mechanism. The proton conductivity of phosphoric acid doped styrene‐maleic imide copolymer can be improved by increasing the acid doping level or the imidazole content. magnified image

Studies on proton conductivity of acid doped polybenzimidazole/polyimide and polybenzimidazole/polyvinylpyrrolidone blends

Polybenzimidazole (PBI)/polyimide (PI) and PBI/polyvinylpyrrolidone (PVP) blends were prepared. All of these polymers are suitable for acid doping as a matrix because of the existence of the N-heterocycle in the polymers, which can eventually be used as proton conductors. The miscibility of PBI/PVP blend is confirmed by Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM), while the miscibility of PBI/PI is already reported in references. Temperature dependence of proton conductivity of acid doped PBI/PI and PBI/PVP blends are studied. As the temperature increases, proton conductivity of H3PO4 doped PBI/PVP blends increases. Temperature dependence of proton conductivity of the blends can still be fitted by a simple Arrhenius relation. The proton transport of the blend is similar to that of PBI. The methanol permeability of PBI/PI blends is also studied. Methanol permeability in PBI/PI, PI, and PBI membranes decreases with increasing methanol concentration. POLYM. ENG. SCI., 45:1395–1400, 2005. © 2005 Society of Plastics Engineers

Proton-Conductive Electrolyte Consisting of NH 4 PO 3 / TiP2 O 7 for Intermediate-Temperature Fuel Cells

A new proton-conductive electrolyte consisting of was synthesized for use in intermediate-temperature fuel cells, and its electrochemical properties were studied in the temperature range 150-300°C. For each composite electrolyte, the X-ray diffraction pattern was identical to that for and was not detected due to a change to an amorphous state at sintering temperature. The proton conductivity of the composite electrolyte was improved by increasing the molar ratio of under both dry and wet atmospheres. These results indicate that is responsible for high proton conductivity and that serves as a supporting matrix. However, under each atmosphere, the temperature dependence of proton conductivity showed non-Arrhenius-type behavior and was almost reversible. Higher proton conductivities were observed at 200-250°C and 150-200°C under dry and wet atmospheres, respectively. For the highest proton conductivity was determined to be at 250°C and at 200°C under dry and wet atmospheres, respectively. Fuel cells that used (electrolyte thickness 2.5 mm) as an electrolyte were fabricated and showed good performance at 250°C. The maximum power density was when dry hydrogen and dry oxygen were used as the fuel and oxidant, respectively. © 2004 The Electrochemical Society. All rights reserved.

Preparation and proton conductivity of poly(N‐methylbenzimidazole) doped with acid

AbstractTo increase the solubility and film forming ability of polybenzimidazole (PBI), poly(N‐methylbenzimidazole) (PNMBI) with different degrees of methylation was synthesized. Chemical structure, degree of substitution, and solubility of PNMBI was studied. PNMBI is easier to be doped with acid than PBI. The basicity of PNMBI was improved with the introduction of methyl groups on the imidazole moiety. Effects of methylation degree, H3PO4 content and temperature on proton conductivity of PNMBI doped H3PO4 was studied. Proton conductivity of H3PO4 doped PNMBI‐1.2 membranes increases with increasing doping level. Temperature dependence of proton conductivity of H3PO4 doped PNMBI‐1.2 membranes follows the Arrhenius law. With an increase in the degree of substitution, proton conductivity of H3PO4 doped PNMBI decreases dramatically. The proton transport mechanism was also discussed. The proton conductivity of PNMBI/H3PO4 is mainly contributed by proton hopping or Grotthuss mechanism. Copyright © 2004 John Wiley & Sons, Ltd.

Protonic conductivity of neutral and acidic silicotungstates

The salts of composition Me 4− x H x SiW 12O 40· nH 2O (Me=Na, K, Rb, Cs, NH 4) are synthesized; their thermal stability, temperature dependence of proton conductivity and structure of protonhydrate shell are studied. The proton conductivity is shown to depend on both the number of acidic protons and polarizability of salt-forming cation of alkaline metal. The presence of differently hydrated protons is discovered in both acidic and neutral salts of 12-silicotungstic acid.