- Direct electrochemical synthesis of oxygenates from ethane using phosphate-based electrolysis cells
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Ethane was converted directly to acetaldehyde and ethanol by partial oxidation at 220 °C and ambient pressure using an electrolysis cell with a proton-conducting electrolyte, CsH2PO4/SiP2O7, and Pt/C electrodes. The ethane conversion and the selectivity to the products increased with the voltage applied to the cell. It was found that O species generated by water electrolysis functioned as a favorable oxidant for partial oxidation of ethane on the Pt/C anode at intermediate temperatures. The production rates of acetaldehyde and ethanol recorded in this study were significantly higher than those in preceding reports.
- Fujiwara, Naoya,Honda, Yusuke,Kikuchi, Ryuji,Kobayashi, Yasukazu,Oyama, Shigeo Ted,Tada, Shohei
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- TEMPERATURE VARIATIONS OF OPTICAL INDICATRIX AND BIREFRINGENCE IN FERROELECTRIC CsH2PO4.
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The principal values and the rotation angle of the optical indicatrix and the optical birefringence of CsH//2PO//4 have been measured at 589 nm as a function of temperature both in the paraelectric and the ferroelectric phases. Rotation of the optical indicatrix with temperature about the b-axis is within 1 degree between 100 K and 300 K. The spontaneous birefringence determined for (010) plate by the usual procedure reaches a maximum at about 15 K below T//c, then becomes negative with decreasing temperature. Similar behavior is found for (100) plate. It is found that these anomalous behaviors of the spontaneous birefringence are caused by the similar anomalous behavior in the spontaneous strain through the elastooptic coupling.
- Ushio
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- An oxide ion and proton co-ion conducting Sn0.9In 0.1P2 O7 electrolyte for intermediate- temperature fuel cells
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The ionic conductivity of Sn0.9In0.1P2 O7 ceramic was investigated under various atmospheres within the temperature range of 130-230°C. Similar to mixed-conductive perovskite oxides at high temperatures (such as SrCe0.95Yb0.05 O 3-α, La0.9 Sr0.1Ga0.8 Mg 0.2 O3-α at 600-1000°C), Sn0.9In 0.1P2 O7 can conduct both protons and oxide ions at low temperatures (130-230°C). The conductivity of Sn 0.9In0.1P2 O7 reaches 0.019 Scm at 200°C in wet nitrogen. Its transport numbers determined by steam concentration cells are around 0.76 for a proton and 0.12 for an oxide ion. The performance of direct methanol fuel cells at 170°C using mixed-ion conductive Sn0.9In0.1P2 O7 electrolyte is higher than that at 235°C using pure proton conductive CsH2PO4 electrolyte. This is attributed to direct oxidation of CO at the anode by the oxide ions generated at the cathode and moved through the Sn0.9In0.1P2 O7 electrolyte.
- Chen, Xilin,Wang, Chunsheng,Payzant, E. Andrew,Xia, Changrong,Chu, Deryn
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- Thermal analysis of CsH2PO4 nanoparticles using surfactants CTAB and F-68
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A study concerned to thermogravimetric analysis is performed in cesium dihydrogen phosphate (CsH2PO4) that was synthesized, using cetyltrimethylammonium-bromide (CTAB), polyoxyethylene-polyoxypropylene (F-68) and mixture of (F-68:CTAB) with two mole ratio 0.06 and 0.12 as surfactant. The dehydration behavior of particles was studied using thermal gravimetric analysis and differential scanning calorimetric. Subsequently, the experimental results indicated that the first dehydration temperature in the range of 237-239 °Cupon heating, the second peaks occur at temperature range 290-295 °C and overlapping in the thermogravimetric events is observed. The mass loss values are obtained in the range of 6.62-6.97 wt% that is less than reported theoretical value 7.8 wt%. These values show well compatibility of reaction CsH2PO4 to Cs2H2P2O 7 with 3.92 wt% whereas mass loss value of CsH2PO 4 to CsPO3 is less than theoretical value 7.8 wt%. The activation energy of two steps dehydration are calculated using Kissinger equation for the samples synthesized via CTAB and (F-68) with minimum value mass loss 6.62% and maximum value mass loss 6.97%, respectively. The calculation results reveal that the reaction rate in the first step (CsH2PO 4 → Cs2H2P2O7) is faster than the second step (CsH 2PO4 → CsPO3). The weight loss values of the samples demonstrate that existence of CTAB can be considered as effective factor which prevents more weight loss during the dehydration process. Akademiai Kiado, Budapest, Hungary 2009.
- Hosseini,Mohamad,KaHum,Wan Daud
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- Effect of silica on the thermal behaviour and ionic conductivity of mixed salt solid acid composites
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The effect of adding silica (SiO2) to a mixed-salt solid acid composite, CsH2PO4/NaH2PO4, was studied via conductivity measurements, thermal analyses and X-ray diffraction. The conductivity value of the composites ranged from 1.1?×?10?4?S?cm?1to 7.6?×?10?3?S?cm?1for temperatures from 210?°C to 250?°C, respectively. Adding NaH2PO4to the composite reduced the conductivity value at 230?°C due to the decomposition of NaH2PO4, which initiated at 210?°C. Dehydration of CsH2PO4was evident at 230?°C and 270?°C, while the superprotonic phase transition was not observed. Dehydration was detected for NaH2PO4at temperatures above 210?°C, but a thermally stable composite was produced by mixing it with CsH2PO4and SiO2. An X-ray diffraction analysis confirmed the existence of solid acid solutions for the composites consisting of NaH2PO4:CsH2PO4and SiO2:CsH2PO4in molar ratios of 1:10 to 3:10. The presence of SiO2partially obstructed the dehydration of the composite, as the diffraction intensity of the dehydration by-product Cs2H2P2O7decreased at the end of the thermal treatment.
- Mohammad, Norsyahida,Mohamad, Abu Bakar,Kadhum, Abdul Amir H.,Loh, Kee Shyuan
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- Electrical and thermodynamic properties of Cs0.97 Rb 0.03H2PO4
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The transport properties of Cs0.97Rb0.03H 2PO4 have been studied using polycrystalline samples and single crystals. The mixed salt is isostructural with cesium dihydrogen phosphate and has slightly smaller unitc
- Lavrova,Martsinkevich,Ponomareva
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- POLARIZED INFRARED AND RAMAN SPECTRA OF MONOCLINIC CsH2PO4 SINGLE CRYSTAL AND ITS DEUTERATED HOMOLOGUE CsD2PO4 Part 1. Hydrogen bond study
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The object of clearly distinguishing the stretching modes originating from the short (ν2) and long (ν1) hydrogen bond in CsH2PO4 has been achieved by recording polarized spectra on the (010) plane using different orientations of the electric vector component.Band parameters of the ν1 stretching mode are taken as a function of the temperature.Calculations of the orientation of the transition dipole moments for the six proton vibrations (ν1, δ1, γ1 and ν2, δ2, γ2) are performed and correlated with the experimental results.
- Videnova-Adrabinska, V.,Baran, J.
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- CRITICAL SLOWING-DOWN AND STATIC DIELECTRIC CONSTANT OF MONOCLINIC RbD2PO4.
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The real and imaginary parts of the complex dielectric constant along the b axis of monoclinic RbD//2PO//4 were measured in a frequency range between 10**6 Hz and 10**9 Hz. It was found that RbD//2PO//4 shows dielectric critical slowing-down near the ferrielectric phase transition point. In addition, the static dielectric constants ( epsilon //0) of RbD//2PO//4 and the partially deuterated crystal Rb(D//0//. //3H//0//. //7)//2PO//4 were also measured at 10**4 Hz. A theoretical expression of epsilon //0 for a ferrielectric phase transition was obtained on the basis of the quasi-one-dimensional Ising model with assumed two sublattices. The remarkable deviations of epsilon //0 from the Curie-Weiss law observed in these crystals were analyzed successfully by the present theoretical result and the experimental results were discussed.
- Komukae,Makita
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- X-ray structural study of ferroelectric cesium dihydrogen phosphate at room temperature
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The atomic coordinates and the anisotropic thermal parameters of CsH 2PO4 crystal in the paraelectric phase have been obtained using three-dimensional X-ray intensity data collected by a four-circle automatic diffractometer at room temperature. The structure is refined to R=0.029 for 780 independent reflections. Two types of hydrogen bonds are clearly distinguished in the electron density maps which display distributions corresponding to order and disorder of protons, respectively.
- Matsunaga, Hironori,Itoh, Kazuyuki,Nakamura, Eiji
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- Intermediate-temperature fuel cell employing CsH2PO 4/SiP2O7-based composite electrolytes
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The proton-conductive electrolytes based on CsH2 PO4 SiP2 O7 composites with various molar ratios were synthesized, and their structural and electrochemical properties were investigated at intermediate temperatures. The interfacial chemical reaction betwe
- Matsui, Toshiaki,Kukino, Tomokazu,Kikuchi, Ryuji,Eguchi, Koichi
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- Platinum-decorated carbon nanotubes for hydrogen oxidation and proton reduction in solid acid electrochemical cells
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Pt-decorated carbon nanotubes (Pt-CNTs) were used to enhance proton reduction and hydrogen evolution in solid acid electrochemical cells based on the proton-conducting electrolyte CsH2PO4. The carbon nanotubes served as interconnects to the current collector and as a platform for interaction between the Pt and CsH2PO4, ensuring minimal catalyst isolation and a large number density of active sites. Particle size matching was achieved by using electrospray deposition to form sub-micron to nanometric CsH2PO4. A porous composite electrode was fabricated from electrospray deposition of a solution of Pt-CNTs and CsH2PO4. Using AC impedance spectroscopy and cyclic voltammetry, the total electrode overpotential corresponding to proton reduction and hydrogen oxidation of the most active electrodes containing just 0.014 mg cm-1 of Pt was found to be 0.1 V (or 0.05 V per electrode) at a current density of 42 mA cm-2 for a measurement temperature of 240°C and a hydrogen-steam atmosphere. The zero bias electrode impedance was 1.2 Ω cm2, corresponding to a Pt utilization of 61 S mg-1, a 3-fold improvement over state-of-the-art electrodes with a 50× decrease in Pt loading.
- Thoi, V. Sara,Usiskin, Robert E.,Haile, Sossina M.
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- Electrical conductivity and thermal stability of (1-x)CsH 2PO4/xSiPyOz (x = 0.2-0.7) composites
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The physicochemical properties of (1 - x)CsH2PO4/xSiP y O z (x = 0.2-0.7) composites containing fine-particle silicon phosphates as heterogeneous additives have been studied at different humidities. The introduc
- Ponomareva,Shutova,Lavrova
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- Surfactant effect on the conductivity behavior of CsH2PO 4: Characterization by electrochemical impedance spectroscopy
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Cesium dihydrogen phosphate (CDP) nanoparticles were synthesized using the surfactants cetyltrimethyl ammonium bromide (CTAB), polyoxyethylenepolyoxypropylene (F-68) and (F-68:CTAB) with molar ratio 0.06. The samples conductivity such as CDPCTAB, CDPF-68 and CDP(F-68:CTAB)0.06 was studied by impedance spectroscopy in the frequency range 0.01 Hz to 1 MHz. The Nyquist plots were drawn at different temperatures of 210, 230 and 260 °C, which are defined below transition, phase transition and above transition, respectively. The measured conductivities obey the Arrhenius relation. The influence of surfactants on conductivity are more significant at higher temperature due to grain boundary. The conductivity of CDPCTAB increased slightly with increasing temperature to 260 °C, whereas the conductivity of other samples decreased with increasing temperature over 230 °C. The results indicated that the conductivities increase in the order of CDPCTAB>CDP (F-68:CTAB)0.06>CDPF-68. These are in accordance to the ion exchange capacities of the samples that the surfactant shows a direct influence on the samples proton mobility. It is found that the conductivity of CsH2PO4 is influenced by surfactant type.
- Hosseini,Homaiee,Mohamad,Malekbala,Khadum
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- Crystal structure and proton conductivity of a new Cs3(H2PO4)(HPO4)·2H2O phase in the caesium di- and monohydrogen orthophosphate system
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The MxHy(AO4)z acid salts (M = Cs, Rb, K, Na, Li, NH4; A = S, Se, As, P) exhibit ferroelectric properties. The solid acids have low conductivity values and are of interest with regard to their thermal properties and proton conductivity. The crystal structure of caesium dihydrogen orthophosphate monohydrogen orthophosphate dihydrate, Cs3(H1.5PO4)2·2H2O, has been solved. The compound crystallizes in the space group Pbca and forms a structure with strong hydrogen bonds connecting phosphate tetrahedra that agrees well with the IR spectra. The dehydration of Cs3(H1.5PO4)2·2H2O with the loss of two water molecules occurs at 348-433K. Anhydrous Cs3(H1.5PO4)2 is stable up to 548K and is then converted completely into caesium pyrophosphate (Cs4P2O7) and CsPO3. Anhydrous Cs3(H1.5PO4)2 crystallizes in the monoclinic C2 space group, with the unit-cell parameters a = 11.1693(4), b = 6.4682(2), c = 7.7442(3)? and β = 71.822(2)°. The conductivities of both compounds have been measured. In contrast to crystal hydrate Cs3(H1.5PO4)2·2H2O, the dehydrated form has rather low conductivity values of 6 × 10-6-10-8 S cm-1 at 373-493K, with an activation energy of 0.91 eV.
- Ponomareva, Valentina,Bagryantseva, Irina,Zakharov, Boris,Bulina, Natalia,Lavrova, Galina,Boldyreva, Elena
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- A study of thermal behavior of cesium phosphate
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Cesium phosphates with different Cs/P molar ratios were prepared by a solution evaporation method. X-ray powder diffraction, thermogravimetric, and differential thermal analyses were performed in order to reveal the chemical transformation and phase compositions which take place during the heating of the mixtures Cs2CO3/(NH4)2HPO4 and CsNO3/(NH4)2HPO4 as well as individual compound. The effects of the Cs/P molar ratio, Cs source and treatment temperature on thermal behavior of the cesium phosphates were investigated. The results showed that different reactions take place with molar ratio from 1/2 to 3/1. Meanwhile, the thermostability of Cs2CO3 and CsNO3 intimately affects the phase composition and phase transition during heating process. However, for all the Cs–P oxides samples, the crystallinity was decreased differently after higher temperature treatment.
- Zhang, Guoliang,Peng, Zhijian,Li, Chunshan
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p. 1063 - 1070
(2016/07/06)
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- Structure of Cs1 - X Rb x H2PO4 solid solutions
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Cs1 - x Rb x H2PO4 solid solutions have been synthesized for the first time in a broad composition range, x = 0.03-0.9. At room temperature, the Cs1 - x Rb x H2PO4 solid solutions are isostructural with the low-temperature phase of CsH2PO4 over the entire composition range studied. In the CsH2PO4-based solid-solution series, the unit-cell parameters and volume decrease with increasing Rb content. At high temperatures, the Cs1 - x Rb x H2PO4 solid solutions exist in the range x = 0-0.4, are isostructural with cubic CsH2PO4, and have a smaller unit-cell parameter.
- Martsinkevich,Ponomareva,Drebushchak,Lavrova,Shatskaya
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p. 765 - 769
(2010/10/04)
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- High-temperature thermal behaviors of XH2PO4 (X = Cs, Rb, K, Na) and LiH2PO3
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XH2PO4 ionic compounds have emerged as a viable electrolyte for intermediate temperature fuel cells, and here have been subjected to thermal analysis to clarify their high-temperature properties. Thermoanalytical peaks were identified at 231.5, 239 and 349 °C for CsH2PO4; 127, 250 and 354 °C for RbH2PO4; 232, 270 and 319 °C for KH2PO4; 223, 330 and 352 °C for NaH2PO4; also, 195 and 220 °C for LiH2PO3 (peak temperature values as measured at the same heating rate of 10 K/min). The thermal events at 231.5 °C in CsH2PO4 and 127 °C in RbH2PO4 were previously interpreted as thermal decomposition by numerous researchers, but we confirm their origin in structural phase transition. The high-temperature variations in KH2PO4 and NaH2PO4 are entirely due to thermal dehydration rather than phase transition. We have also examined LiH2PO3, and found, for the first time, an endothermic peak at 195 °C, and attributed it to structural phase transition.
- Li, Zikun,Tang, Tongbor
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- Electrochemical hydrogen production from carbon monoxide and steam with a cell employing CsH2 PO4 / SiP2 O7 composite electrolyte
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Electrochemical hydrogen pumping was investigated with a cell consisting of a CsH2 PO4 / SiP2 O7 composite electrolyte at 200°C. When humidified hydrogen was fed to the anode, the evolution rate of hydrogen at t
- Muroyama, Hiroki,Matsui, Toshiaki,Kikuchi, Ryuji,Eguchi, Koichi
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p. B1389-B1393
(2010/01/06)
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- High-temperature phase transitions in CsH2PO4 under ambient and high-pressure conditions: A synchrotron x-ray diffraction study
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To clarify the microscopic origin of the temperature-induced three-order-of-magnitude jump in the proton conductivity of Cs H2 P O4 (superprotonic behavior), we have investigated its crystal structure modifications within the 25-300 °C temperature range under both ambient- and high-pressure conditions using synchrotron x-ray diffraction. Our high-pressure data show no indication of the thermal decomposition/polymerization atthe crystal surface recently proposed as the origin of the enhanced pro ton conductivity [Phys. Rev. B 69, 054104 (2004)]. Instead, we found direct evidence that the superprotonic behavior of the title material is associated with a polymorphic structural transition to a high-temperature cubic phase. Our results are in excellent agreement with previous high-pressure ac impedance measurements.
- Botez, Cristian E.,Hermosillo, Juan D.,Zhang, Jianzhong,Qian, Jiang,Zhao, Yusheng,et al.
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- Possible origin of the proton conduction mechanism of CsH 2PO4 crystals at high temperatures
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The high-temperature transformation of CsH2PO4 was studied by means of impedance spectroscopy, differential thermal analysis, and thermogravimetric methods. The dielectric constant showed a high-temperature anomaly around Tp = 230 °C. The thermal transformation which appears around Tp = 230 °C is endothermic in addition to showing weight loss. Our results show evidence that the high-temperature transformation of CsH2PO4 near Tp is not a structural phase transition, but an onset of thermal decomposition of CsH2PO 4 into CsnH2PnO3n+1 [probably n ? 1, (CsPO3)n] at reaction sites at the surface of the crystal. From complex ac impedance spectra, we observed impedance consisting of two regions for measuring frequency: the low-frequency region may be due to the formation and migration of H2O molecules at the surface while the conduction mechanism of the high-frequency region seems to be Cole-Cole type and may be due to the proton migration in the bulk. Our results support that the phase of CsH2PO4 above T p is not a superionic conductor phase caused by a structural transition (monoclinic→cubic) but rather a polymeric state caused by partial thermal decomposition. The possible origin of proton conduction for CsH2PO4 is considered to be the partial thermal decomposition of the crystal surface because the polymeric transition tends to increase breaking and reforming of the hydrogen bond at the surface.
- Park J.-H.
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