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1.
This study deals with the relationship between open-circuit potential and catalytic activity of the system Pt/YSZ. Temperature-programmed
desorption (TPD) of oxygen was carried out in order to investigate the link between the oxygen coverage and the potential.
Then, catalytic activity in parallel with the potential value was measured between 200 °C and 500 °C for NO oxidation, C 3H 8 combustion, C 3H 6 combustion and the selective catalytic reduction (SCR) of NO by C 3H 6 in the presence of oxygen. It was found that potential measurement can give precious information on the competitive adsorption
between oxygen and other reactants. Finally, it seems to be also a good way to anticipate the NEMCA behavior for reactions,
which involve oxygen.
Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004. 相似文献
2.
The catalytic activity of polycrystalline Pt deposited on Yttria Stabilized Zirconia (YSZ) for the oxidation of propane to
CO 2 can be affected using the effect of Non-faradaic Electrochemical Modification of Catalytic Activity (NEMCA). It was found
that by applying positive overpotentials and thus, supplying O 2- onto catalyst surface, up to 3.2-fold increase in the catalytic rate of C 3H 8 oxidation could be obtained at 365 °C. At 305 °C, no effect was evidenced. Using cyclic voltammetry and impedance spectroscopy,
we have shown the modifications induced by the addition of C 3H 8 on the kinetics of the 0 2, Pt/YSZ interface in the temperature range 300–400 °C. A decrease of the coverage of adsorbed oxygen species produced electrochemically
was evidenced as well as a decrease of the oxygen electrode reaction rate under anodic potential.
Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001. 相似文献
3.
Thin sodium superionic conductor (Nasicon) coatings are deposited on rotating substrates by co-sputtering in the reactive
mode of a Zr-Si and a Na 3PO 4 target. The influence of the discharge current and of the target-to-substrate distance is investigated owing to the targeted
Na 3Zr 2Si 2PO 12 stoichiometry. A thermo-structural analysis shows that the amorphous as-deposited coating of convenient composition crystallises
around 700 °C in the monoclinic structure. Electrical measurements performed at room temperature after various annealing treatments
indicate a ionic conductivity of about 2·10 −3 S·cm −1, consistent with that of bulk Nasicon.
Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004. 相似文献
4.
Two Pt/C catalysts with different particle sizes (Pt/C: 2.5 nm, Pt/C-700Ar: 5.1 nm) were investigated by applying a half-cell
configuration — rotating disk electrode (RDE) technique in H 2SO 4 aqueous solutions in the absence of or in the presence of methanol with different concentrations. Pt/C catalyst exhibited
higher mass activity in H 2SO 4 aqueous solution without methanol and slightly lower mass activity in H 2SO 4 plus 0.1 mol/L CH 3OH in comparison with that of Pt/C-700Ar catalyst. On the contrary, single direct methanol fuel cell (DMFC) tests showed that Pt/C exhibited higher oxygen reduction reaction (ORR) activity and better cell performance, mainly due to the different kinds of electrolyte properties. Furthermore, it
suggested that a better single DMFC performance could be obtained with a smaller particle size Pt-based cathode catalyst.
Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 — 18, 2004. 相似文献
5.
Nanosized IrO 2 electrocatalysts ( d ~ 7–9 nm) with specific surface area up to 100 m 2 g −1 were synthesized and characterized for the oxygen evolution reaction in a solid polymer electrolyte (SPE) electrolyzer. The
catalysts were prepared by a colloidal method in aqueous solution and a subsequent thermal treatment. An iridium hydroxide
hydrate precursor was obtained at ~100 °C, which was, successively, calcined at different temperatures from 200 to 500 °C.
The physico-chemical characterization was carried out by X-ray diffraction (XRD), thermogravimetry–differential scanning calorimetry
(TG–DSC) and transmission electron microscopy (TEM). IrO 2 catalysts were sprayed onto a Nafion 115 membrane up to a loading of 3 mg cm −2. A Pt catalyst was used at the cathode compartment with a loading of 0.6 mg cm −2. The electrochemical activity for water electrolysis of the membrane-electrode assemblies (MEAs) was investigated in a single
cell SPE electrolyzer by steady-state polarization curves, impedance spectroscopy and chrono-amperometric measurements. A
maximum current density of 1.3 A cm −2 was obtained at 1.8 V and 80 °C for the IrO 2 catalyst calcined at 400 °C for 1 h. A stable performance was recorded in single cell for this anode catalyst at 80 °C. The
suitable catalytic activity and stability of the most performing catalyst were interpreted in terms of proper combination
between nanostructure and suitable morphology. 相似文献
6.
This article describes a method for silica coating of Co–Pt alloy nanoparticles prepared in the presence of poly(vinylpyrrolidone)
(PVP) as a stabilizer. The Co–Pt nanoparticles were prepared in an aqueous solution at 25–80 °C from CoCl 2 (3.0 × 10 −4 M), H 2PtCl 6 (3.0 × 10 −4 M), PVP (0–10 g/L), and NaBH 4 (4.8 × 10 −3–2.4 × 10 −2 M). The silica coating was performed for the Co–Pt nanoparticle colloid containing the PVP ([Co] = [Pt] = 3.0 × 10 −5 M) at 25 °C in (1/4) (v/v) water/ethanol solution with tetraethoxyorthosilicate (TEOS) (7.2 × 10 −5–7.2 × 10 −3 M) and ammonia (0.1–1.0 M). Silica particles, which had an average size of 43 nm and contained multiple cores of Co–Pt nanoparticles
with a size of ca. 8 nm, were produced at 1.4 × 10 −3 M TEOS and 0.5 M ammonia after the preparation of Co–Pt nanoparticles at 80 °C, 5 g/L PVP, and 2.4 × 10 −2 M NaBH 4. Their core particles were fcc Co–Pt alloy crystallites. Their saturation magnetization was 2.0-emu/g sample, and their coercive
field was 12 Oe. 相似文献
7.
Ce 0.9Gd 0.1O 1.95 (GCO), is one of the potential candidate electrolytes for intermediate temperature Solid Oxide Fuel Cells (ITSOFC). GCO has
high oxide ion conductivity in the intermediate temperature range (500 – 700 °C) compared to other Ce 1−yGd yO 2-2/y compositions and the Gd 3+ ion is the most appropriate dopant material compared to other rare earth materials such as Sm 3+, Y 3+, Zr 3+, etc. Our results show that the fuel cell H 2/Pt/Ce 0.9Gd 0.1O 1.95/Pt/O 2 operated in the temperature range 500 – 700°C gives the maximum power densities 0.0049 W/cm 2 at 500 °C and 0.0126 W/cm 2 at 650 °C for cell voltages 0.6275 V and 0.6278 V, respectively, where the electrolyte was kept in 5% H 2 (+ Argon) for 12 hours before use in the fuel cell. Maximum power densities are 0.0038 W/cm 2 at 500 °C and 0.0270 W/cm 2 at 650 °C for cell voltages 0.5986 and 0.5913 V, respectively, where the electrolyte was kept in 2 % O 2 (+ Argon) for 12 hours before use in the fuel cell.
Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003. 相似文献
8.
SrBi 2Ta 2O 9 (SBT) ferroelectric thin films with different preferred orientations were deposited by pulsed laser deposition (PLD). Several
methods have been developed to control the preferred orientation of SBT thin films. For SBT films deposited directly on Pt/TiO 2/SiO 2/Si substrates and in situ crystallized at the deposition temperature, the substrate temperature has a significant impact
on the orientation and the remnant polarization (Pr) of the films; a higher substrate temperature benefits the formation of
(115) texture and larger grain size. The films deposited on Pt/TiO 2/SiO 2/Si substrates at 830 °C are (115)-oriented and exhibit 2Pr of 6 μC/cm 2. (115)- and (200)-predominant films can be formed by using a La 0.85Sr 0.15CoO 3 (LSCO) buffer layer or by annealing amorphous SBT films deposited on Pt/TiO 2/SiO 2/Si substrates at 450 °C using rapid thermal annealing (RTA). These films exhibit good electric properties; 2Pr of the films
are up to 12 μC/cm 2 and 17 μC/cm 2, respectively. The much larger 2Pr of the films deposited on the LSCO buffer layer and of the films obtained by RTA than
2Pr of the films deposited on Pt/TiO 2/SiO 2/Si substrates at 830 °C is attributed to a stronger (200) texture.
Received: 30 January 2001 / Accepted: 30 May 2001 / Published online: 25 July 2001 相似文献
9.
The resistive response of atomic layer deposited thin epitaxial α-Cr 2O 3(0 0 1) films, to H 2 and CO in air, was studied. The films were covered with Pt nanoislands formed by electron-beam evaporation of a sub-monolayer
amount of the material. The gas measurements were performed at 250°C and 450°C. These temperatures led to different proportion
of chemical states, Pt 2+ and Pt 4+, to which the Pt oxidized. The modification was ascertained by the X-ray photoelectron spectroscopy method. As a result of
the modification, the response was fast at 250°C, but slowed at 450°C. A disadvantageous abundance of Pt 4+ arising at 450°C in air could be diminished by high-vacuum annealing thus restoring the response properties of the system
at 250°C.
相似文献
10.
The effect of non-faradaic electrochemical modification of catalytic activity (NEMCA effect) or electrochemical promotion (EP) was investigated in the total oxidation of propane on porous Pt and Rh catalyst-electrode films interfaced to 8 mol% Y 2O 3-stabilized-ZrO 2 (or YSZ), in the temperature range 425–520 °C and for sub-stoichiometric O 2 to propane ratios. Application of either positive or negative overpotentials resulted in non-faradaic increase of the catalytic rate, by up to a factor of 4 in the case of Rh and by up to a factor of 1350 in the case of Pt. The rate increase observed in the case of Pt is among the highest ones reported so far in NEMCA studies with oxygen ion conductors as active supports. 相似文献
11.
A platinum/reduced graphene oxide (Pt/rGO) nanocomposite acting as a counter electrode (CE) was fabricated using a chemical bath deposition method for In2O3-based dye-sensitized solar cell (DSSC) via sol-gel technique. The report analyzes the morphological and electrochemical impedance spectroscopy of the annealing Pt/rGO films at 350, 400, and 450 °C. Micrograph images obtained from field emission scanning electron microscopy demonstrated the annealed films are highly porous. The energy-dispersive X-ray results show that the carbon atoms were homogeneously distributed on the film annealed at 400 °C. A good photovoltaic performance was exhibited with high photocurrent density of 8.1 mA cm−2 and power conversion efficiency (η) of 1.68 % at the Pt/rGO CE annealed at 400 °C. The employed electrochemical impedance spectroscopy analysis quantifies that the Pt/rGO films annealed at 400 °C provide more efficient charge transfer with the lowest effective recombination rate and high electron life time, hence improving the performance of Pt/rGO CE. 相似文献
12.
Monometallic Pt and Rh and bimetallic PtRh catalysts with a highly dispersed noble metal weight loading of ca. 1 wt% were
produced via the direct deposition of nanoparticles on different SiO 2 supports by means of pulsed ultra-violet (248 nm) excimer laser ablation of Pt, Rh bulk metal and PtRh alloy targets. Backscattered
electron microscopy (BSE), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM) were employed
to characterize the deposited nanoparticles, which were found to exhibit narrow size distribution centred around 2.5 nm. The
catalytic activities for lean NO
x
reduction of the monometallic and bimetallic catalyst samples were investigated in a flow reactor setup in the temperature
range 100–400°C using a test gas mixture representative of oxygen rich diesel engine exhaust gas. For comparison a Rh/SiO 2 reference catalyst prepared by a conventional impregnation method was also tested. Further experiments were performed in
which PtRh nanoparticles were deposited on a Rh/SiO 2 reference catalyst sample to study the possibility for controlled modification of its activity. The catalytic activity measurements
revealed that among the samples solely prepared by laser deposition the PtRh–SiO 2 nanoparticle catalyst showed the highest activity for NO
x
reduction at low temperatures 100–300°C. In addition, it could be demonstrated that the initially low NO
x
reduction activity and the N 2 selectivity of the Rh/SiO 2 reference catalyst sample for temperatures below 250°C can be enhanced by post laser deposition of PtRh nanoparticles. 相似文献
13.
The catalytic oxidation of dodecane by air oxygen on a mixed vanadium-molybdenum oxide (V 2O 5 · MoO 3, 40 mol % MoO 3) was studied over the temperature range 300–350°C. The reaction at 300–330°C occurred on oxygen vacancies with the rupture
of C-H bonds and formation of α-acid. Oxidation above 350°C occurred with the splitting of the C-C bond and formation of two
and more acids. Singlet oxygen 1O 2 generated in the oxidation of oxide catalyst lattice oxygen participated in the reaction. A possible mechanism of the process
was considered. 相似文献
14.
The effect of non-Faradaic electrochemical modification of catalytic activity (NEMCA) or electrochemical promotion (EP) was
investigated on Pt films deposited on Y 2O 3-stabilized-ZrO 2 (YSZ), an O 2− conductor, TiO 2, a mixed conductor, and Nafion 117 solid polymer electrolyte (SPE), a H + conductor and also on Pd films deposited on YSZ and β″-Al 2O 3 a Na + conductor. Four catalytic systems were investigated, i.e. C 2H 6 oxidation on Pt/YSZ, C 2H 4 oxidation on Pd/YSZ and Pd/β″-Al 2O 3, C 2H 4 oxidation on Pt/TiO 2 and H 2 oxidation on Pt/Nafion 117 in contact with 0.1 M aqueous KOH solution.
In all cases pronounced and reversible non-Faradaic electrochemical modification of catalytic rates was observed with catalytic
rate enhancement up to 2000% and Faradaic efficiency values up to 5000.
All reactions investigated exhibit a pronounced electrophobic behaviour which is due to the weakening of chemisorptive oxygen
bond at high catalyst potentials. Ethane oxidation, however, also exhibits electrophilic behaviour at low potentials due to
weakened binding of carbonaceous species on the surface.
The general features of the phenomenon are similar for all four cases presented here showing that the NEMCA effect is a general,
electrochemically induced, promoting catalytic phenomenon not depending on the reaction and the type of supporting electrolyte.
Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995 相似文献
15.
The distinctive features of the low-frequency internal friction Q
−1( T) of (Cu-Sn)-Nb composites at high temperatures (up to 400°C) are investigated for strains in the range 10 −5–10 −4. Considerable hysteresis of Q
−1( T) in the heating-cooling cycle is recorded, including the presence of a minimum at ∼175°C when the sample is heated to 400°C
and two peaks P
2 (at 280°C) and P
1 (at ∼100°C) when the sample is cooled from 400°C. The activation energy of the anomalous internal friction background (up
to 175°C), the oxygen diffusion parameters, and the oxygen concentration in the niobium fibers (all of which govern the peak
P
2) are calculated, and the value and temperature dependence of the yield point of the bronze matrix (which govern the peak
P
1) are estimated.
Zh. Tekh. Fiz. 68, 114–117 (November 1998) 相似文献
16.
Zirconium oxide layers have been successfully deposited by photo-CVD at low temperatures. ZrO 2 growth was observed at temperatures as low as 100 °C. When deposited at 250 °C and above, these films exhibited a polycrystalline
structure with a mixture of different crystal phases. Deposition at 300 °C was found to form moisture-free ZrO 2 films with a high refractive index of 2.1, a very low effective density of trapped electrons of ∼8.8×10 8 cm -2 and an interface trap density of 6.6×10 9 cm -2 eV -1 being readily obtained.
Received: 17 December 2001 / Accepted: 6 January 2002 / Published online: 3 June 2002 相似文献
17.
Thermally stimulated current (TSC) measurements performed in the 100 K–400 K temperature range on Bi 4Ti 3O 12 (BiT) thin films annealed at 550 °C and 700 °C had revealed two trapping levels having activation energies of 0.55 eV and
0.6 eV. The total trap concentration was estimated at 10 15 cm −3 for the samples annealed at 550 °C and 3×10 15 cm −3 for a 700 °C annealing and the trap capture cross-section was estimated about 10 −18 cm 2. From the temperature dependence of the dark current in the temperature range 20 °C–120 °C the conduction mechanism activation
energy was found to be about 0.956–0.978 eV. The electrical conductivity depends not only on the sample annealing temperature
but also whether the measurement is performed in vacuum or air. The results on the dark conductivity are discussed considering
the influence of oxygen atoms and oxygen vacancies.
Received: 28 January 1998 / Accepted: 8 January 1999 / Published online: 5 May 1999 相似文献
18.
The application of the electrophoretic deposition (EPD) technique to the preparation of high quality electrolyte films for intermediate temperature solid oxide fuel cells (IT-SOFCs) was investigated. Films of La 0.83Sr 0.17Ga 0.83Mg 0.17O 2.83 (LSGM) were deposited on Pt and La 0.8Sr 0.2MnO 3 (LSM) substrates from suspensions in acetone/ethanol (3:1 by volume) mixture solvent and sintered at 1300 °C. Pt supported LSGM films, 10–20 μm thick, exhibited good adhesion to the Pt substrate, well-distributed microporosity and some surface roughness. LSM supported films exhibited cracking after sintering at 1300 °C for 3 h. Up to 900 °C the bulk conductivity of the Pt supported LSGM film showed the same behaviour of LSGM pellet ( Ea = 0.93 eV and 0.99 eV, respectively). The LSGM film exhibited lower bulk electrical conductivity than the latter (4.1 × 10 − 3 and 4.4 × 10 − 2 Ω − 1 cm − 1, respectively, at 700 °C). This difference should be ascribed to the slight Ga depletion in the LSGM film. An important issue remains the selection of adequate electrode for LSGM electrolyte films. 相似文献
19.
In the reducing atmosphere of the SOFC anode at operating temperatures of 800 °C and above Nb 2TiO 7 is reduced to Nb 1.33Ti 0.67O 4. This material displays very high electronic conductivity of >100 Scm −1, suitable for use in such applications as a current collector. It has a low thermal expansion coefficient of 3 × 10 −6 K −1, however, which may cause problems due to mismatch with other SOFC components, e.g. YSZ. Doping with Fe 2O 3 successfully increased the thermal expansion to a maximum of 6 × 10 −6 K −1. A conductivity of 140 Scm −1 at 900 °C in dry 5% H 2/Ar, with an activation energy of 0.18 eV, was achieved for the Nb 1.344Ti 0.642Fe 0.014O 4, making it suitable for the use as a current collector. Conductivity runs in wet 5%H 2/Ar showed lower conductivities of 15–18 Scm −1 and lower activation energies of 0.08 − 0.09 eV. Single cell tests of Nb 1.33Ti 0.67O 4 showed power outputs of 5.5 − 7.2 mW·cm −2 at 850 °C, lower than for Ni with 150 − 200 mW·cm −2 at 850 °C, however, this material displayed much better stability at high temperatures than Ni.
Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15 – 21, 2002. 相似文献
20.
This investigation is a contribution to the research on alternative cathode materials with much more promising performances
for lithium batteries. It deals with the electrochemical properties of iron phosphate compound FePO 4, chemically prepared through the so-called sol–gel Pechini process, terminated by a calcination of the product precursor
at temperatures ( T
c) ranging between 350°C and 650°C. A crystalline phase was obtained for temperatures ≥400°C. The particle size decreased with
the decrease in T
c, giving rise to a Brunauer–Emmett–Teller (BET)-specific surface area, S
BET, as high as 28 m 2 g −1 for the sample annealed at 400°C. The electrochemical properties of FePO 4-based composite cathodes were characterized on three-electrode laboratory cells. Charge–discharge cycling determined a maximum
reversible capacity of 132 mAh g −1, which fell with the increase in T
c. A direct correlation was established between the activity of the material and its active surface area. 相似文献
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