Vehikel‐Mechanismus, ein neues Modell zur Deutung der Leitfähigkeit schneller Protonenleiter
About: This article is published in Angewandte Chemie.The article was published on 2006-01-16. It has received 69 citations till now.
Citations
More filters
TL;DR: This is the first joint experimental/modeling study that unambiguously elucidates the proton-conduction mechanism at the molecular level in a highly conductive MOF.
Abstract: The water stable UiO-66(Zr)-(CO2H)2 MOF exhibits a superprotonic conductivity of 2.3×10(-3) S cm(-1) at 90 °C and 95 % relative humidity. Quasi-elastic neutron scattering measurements combined with aMS-EVB3 molecular dynamics simulations were able to probe individually the dynamics of both confined protons and water molecules and to further reveal that the proton transport is assisted by the formation of a hydrogen-bonded water network that spans from the tetrahedral to the octahedral cages of this MOF. This is the first joint experimental/modeling study that unambiguously elucidates the proton-conduction mechanism at the molecular level in a highly conductive MOF.
147 citations
TL;DR: The structure and the local proton mobility of poly(vinyl phosphonic acid) were studied by solid-state NMR under fast magic-angle spinning and it is demonstrated that the conductivity is greatly influenced by the presence of phosphonic Acid anhydride.
Abstract: The structure and the local proton mobility of poly(vinyl phosphonic acid) were studied by solid-state NMR under fast magic-angle spinning. At elevated temperatures, the signature of the hydrogen-bonded P−OH protons is observed in 1H magic-angle spinning (MAS) NMR as a single resonance at 10.5 ppm. Both 1H double-quantum NMR and variable-temperature experiments demonstrate that P−OH protons are mobile and thus able to contribute to proton conductivity. Below room temperature, two different types of hydrogen-bonded P−OH resonances are observed at 10.5 and 15 ppm, and 1H double-quantum NMR demonstrates that these protons are immobile on the NMR time scale. By means of first-principles calculations of a model polymer, we have assigned the additional hydrogen-bonded species at lower temperatures to phosphonic acid anhydride and charged anhydride. Also, in the 31P MAS NMR spectrum, two distinct resonances appear, arising from “normal” phosphonic acid and phosphonic acid anhydride. 31P double-quantum NMR experi...
141 citations
TL;DR: It is found that the gas response of the ammonia sensor increases linearly with the increase of NH3 gas concentration under 68-98 % RH and room temperature, and indicates excellent reversibility and selectivity toward NH3 versus N2, H2, O2, CO, CO2, benzene, and MeOH.
Abstract: This work reports the design and fabrication of a proton conductive 2D metal-organic framework (MOF), [Cu(p-IPhHIDC)]n (1) (p-IPhH3 IDC=2-(p-N-imidazol-1-yl)-phenyl-1 H-imidazole-4,5-dicarboxylic acid) as an advanced ammonia impedance sensor at room temperature and 68-98 % relative humidity (RH). MOF 1 shows the optimized proton conductivity value of 1.51×10-3 S cm-1 at 100 °C and 98 % RH. Its temperature-dependent and humidity-dependent proton conduction properties have been explored. The large amount of uncoordinated carboxylate groups between the layers plays a vital role in the resultant conductivity. Distinctly, the fabricated MOF-based sensor displays the required stability toward NH3 , enhanced sensitivity, and notable selectivity for NH3 gas. At room temperature and 68 % RH, it gives a remarkable gas response of 8620 % to 130 ppm NH3 gas and lower detection limit of 2 ppm towards NH3 gas. It is also found that the gas response of the ammonia sensor increases linearly with the increase of NH3 gas concentration under 68-98 % RH and room temperature. Moreover, the sensor indicates excellent reversibility and selectivity toward NH3 versus N2 , H2 , O2 , CO, CO2 , benzene, and MeOH. Based on structural analyses, activation energy calculations, water and NH3 vapor absorptions, and PXRD determinations, proton conduction and NH3 sensing mechanisms are suggested.
102 citations
TL;DR: Hydrated proton-conductive MOFs show not only high proton conductivity, which is comparable to that of a practical organic polymer, but also structural visibility of Proton conduction pathways inside the materials owing to their high crystallinity.
Abstract: Recent investigations into proton conduction in metal–organic frameworks (MOFs) indicate that MOFs are promising materials as a new class of proton conductors. Hydrated proton-conductive MOFs show not only high proton conductivity of approximately 10−2 S cm−1, which is comparable to that of a practical organic polymer, but also structural visibility of proton-conducting pathways inside the materials owing to their high crystallinity. Herein, studies on the design, synthesis, and proton-conductive properties of MOFs with hydrated proton-conductive systems are introduced.
101 citations
TL;DR: The proton conductivity of highly sulfonated poly(p-phenylene sulfone) polymers are water soluble and brittle in the dry state, but their transport properties together with their high hydrolytical and morphological stability renders this type of ionomer an interesting constituent of polymer electrolyte membrane (PEM) fuel cell membranes able to operate at high temperature and low humidification.
Abstract: Poly(phenylene) ionomers which contain merely sulfone units (–SO2–) connecting the phenyl rings and in which each phenyl ring is sulfonated (–SO3H) have been characterized with respect to their microstructural and transport properties. The high degree of sulfonation leads to the development of a microstructure characterized by very narrow hydrated, hydrophilic domains which are well connected on longer scales. These features together with high absolute water uptakes at given relative humidities and the high charge carrier concentration corresponding to the high ion exchange capacity (IEC ∼ 4.5 milli equivalent g−1) result in very high proton conductivities but also low water transport coefficients (water diffusion and presumably also electroosmotic drag and permeation). Compared to the transport properties of Nafion, these trends increase with increasing water content and with increasing temperature. For a relative humidity of RH = 30% and a temperature of T = 135 °C, the proton conductivity is found to be seven times higher than the conductivity of Nafion under the same conditions. Highly sulfonated poly(p-phenylene sulfone) polymers are water soluble and brittle in the dry state, but their transport properties together with their high hydrolytical and morphological stability renders this type of ionomer an interesting constituent of polymer electrolyte membrane (PEM) fuel cell membranes able to operate at high temperature and low humidification.
98 citations
References
More filters
TL;DR: In this paper, a Grotthus-type mechanism of conduction is proposed which involves intermolecular transfer steps (hopping) and inter-parallel transfer steps in comparable numbers, the former facilitated by the high concentration of H 3 O + ions in the structure, and the latter most likely facilitated by high H-bond vacancies.
Abstract: We have found that hydrogen uranyl phosphate tetrahydrate HUO 2 PO 4 ·4H 2 O has a high proton conductivity. The ac conductivity was 0.4 ohm −1 m −1 at 290°K measured parallel to the faces of sintered disks of the compound. The activation energy was found to be 31 ± 3 kJ mole −1 . The values of conductivity were between 3 and 10 times lower when measured perpendicular to the disk faces due to preferred orientation of the plate-like crystals. Both the powder and sintered disks are stable in air and insoluble in phosphoric acid solution of pH 2.5. Experiments are described which enable possible grain boundary contributions to the conductivity to be determined in such hydrates. The extrinsic grain boundary contribution to the conductivity was found to be small from experiments in which the pH in a solution cell was varied. The abnormally high bulk H + conductivity thus inferred is attributed primarily to the high concentration of H + , which exists as H 3 O + in the interlamellar hydrogen-bonded network. A Grotthus-type mechanism of conduction is proposed which involves intermolecular transfer steps (hopping) and intramolecular transfer steps, in comparable numbers, the former facilitated by the high concentration of H 3 O + ions in the structure, and the latter most likely facilitated by the high concentration of H-bond vacancies.
132 citations
TL;DR: In this paper, single-crystal measurements on hydrogen uranyl phosphate tetrahydrate, HUO 2 PO 4 ·4H 2 O (HUP), have confirmed that the high proton conductivity is a bulk characteristic.
Abstract: Single-crystal measurements on hydrogen uranyl phosphate tetrahydrate, HUO 2 PO 4 ·4H 2 O (HUP), have confirmed that the high proton conductivity is a bulk characteristic. The conductivity values were in substantial agreement with those previously reported for polycrystalline disks. A conductivity of 0.6 ohm −1 m −1 at 290°K and an activation energy of 30 ± 1 kJ mole −1 were measured parallel to the structural layers of the crystal. The conductivity was at least 100 times lower when measured in the perpendicular direction. A reasonable attempt frequency ω 0 of approximately 10 15 Hz could be derived from the parallel conductivity on the assumption that the charge carrier concentration was equal to that of the H 3 O + ions. This implies a low proton mobility, of the order of 10 −9 m 2 V −1 sec −1 at 290°K, in support of previous estimates. We have also shown that polycrystalline hydrogen uranyl arsenate tetrahydrate, HUO 2 AsO 4 ·4H 2 O (HUAs), has a high conductivity of 0.6 ohm −1 cm −1 at 310°K, with an activation energy of 31 ± 2 kJ mole −1 . Below the respective dielectric ordering transition temperatures of HUP and HUAs of 274 and 301°K, the lower conductivity values show a marked frequency dependence, which may be due to dispersion effects caused by water reorientations.
76 citations
TL;DR: In this paper, a vehicle-mechanism for the transport of zeolites is proposed based on an optimized protonic conduction in a fully hydrated NH4-zeolite A.
Abstract: Protonic conduction in zeolites is optimized. The approach is based on a vehicle-mechanism for the transport process. The parameters controlling protonic conduction are discussed. Fully hydrated “NH4-zeolite A” has a room temperature conductivity of 2×10 −3 Ω −1 cm −1 . The material was successfully used in oxygen concentration cells (e.g. MnO2/NH4-zeolite A/Zn).
47 citations
TL;DR: In this article, LiN 2 H 5 SO 4 has been shown to have a conductivity of 2 × 10 −8 ω −1 cm −1 at 25°C and an activation enthalpy of 0.75 ± 0.07 eV.
Abstract: One-dimensional bulk proton conduction parallel to the c axis was observed in solid lithium hydrazinium sulfate, LiN 2 H 5 SO 4 . The conductivity in this direction is 2 × 10 −8 ω −1 cm −1 at 25°C and shows an activation enthalpy of 0.75 ± 0.07 eV. The two-dimensional conductors HUO 2 AsO 4 ·4H 2 O and HUO 2 PO 4 ·4H 2 O were studied as a function of their water content. The conductivities are 8 × 10 −6 and 3 × 10 −5 ω −1 cm −1 in the orthorhombic phase at −10°C, with activation enthalpies of 0.70 ± 0.05 and 0.57 ± 0.07 eV, respectively. Indications of peritectic transitions to the tetragonal phases were observed in the temperature ranges 15 to 47 and −5 to 10°C, respectively. The transition depends on the water content which appears to control the increase in conductivity in this material. The dependence upon various sample parameters is discussed. Fast proton transport in solids is proposed to occur by a “vehicle mechanism”, i.e. the motion of N 2 H + 5 , H 3 O + - or other proton-containing groups.
39 citations
TL;DR: In this article, diffusion and conductivity mechanisms for DUO2AsO4·4D2O (DUAs) are considered in the light of neutron diffraction evidence for partial ordering and the presence of D5O+2 and D4O2 units in the structure.
Abstract: Diffusion and conductivity mechanisms for DUO2AsO4·4D2O (DUAs) are considered in the light of neutron diffraction evidence for partial ordering and the presence of D5O+2 and D4O2 units in the structure.
38 citations