Hydrogen oxidation reaction at the Ni/YSZ anode of solid oxide fuel cells from first principles

By means of ab initio simulations we here provide a comprehensive scenario for hydrogen oxidation reactions at the Ni/zirconia anode of solid oxide fuel cells. The simulations have also revealed that in the presence of water chemisorbed at the oxide surface, the active region for H oxidation actually extends beyond the metal/zirconia interface unraveling the role of water partial pressure in the decrease of the polarization resistance observed experimentally.     

Microstructure and performance of novel Ni anode for hollow fibre solid oxide fuel cells

Nickel anodes were deposited on hollow fibre yttria-stabilised zirconia (YSZ) electrolyte substrates for use in solid oxide fuel cells (SOFCs). The hollow fibres are characterised by porous external and internal surfaces supported by a central gas-tight layer (300 μm total wall thickness and 1.6 mm external diameter). The YSZ hollow fibres were prepared by a phase inversion technique followed by high temperature sintering in the range 1200 to 1400 °C. Ni anodes were deposited on the internal surface by electroless plating involving an initial catalyst deposition step with PdCl₂ followed by Ni plating (with a NiSO₄, NaH₂PO₂ and sodium succinate based solution at 70 °C). Fabrication and nickel deposition parameters (nature of solvents, air gap, temperature, electroless bath composition) and heat treatments in oxidising/reducing environments were investigated in order to improve anode and electrolyte microstructure and fuel cell performance. A parallel study of the effect of YSZ sintering temperature, which influences electrolyte porosity, on electrolyte/anode microstructure was performed on mainly dense discs (2.3 mm thick and 15 mm diameter). Complete cells were tested with both disc and hollow fibre design after a La_0.2Sr_0.8Co_0.8Fe_0.2O_3?δ (LSCF) cathode was deposited by slurry coating and co-fired at 1200 °C. Anodes prepared by Ni electroless plating on YSZ electrolytes (discs and hollow fibres) sintered at lower temperature (1000–1200 °C) benefited from a greater Ni penetration compared to electrolytes sintered at 1400 °C. Further increases in anode porosity and performance were achieved by anode oxidation in air at 1200–1400 °C, followed by reduction in H₂ at 800 °C.     

Effect of anode microstructure on the performance of micro tubular SOFCs

Here we report the effect of anode microstructure on the SOFC performance using two types of micro tubular SOFCs, 0.8 and 1.6mm in diameter with different anode microstructure (Cells A and B). The cells consisted of NiO-Gd doped ceria (GDC) as an anode (support tube), GDC as an electrolyte and (La, Sr)(Fe, Co)O₃ (LSCF)-GDC as a cathode. The anode tube for Cell A was prepared using NiO (d_g~ 5µm) and GDC (d_g~ 0.2µm) powders without using a pore former, while the anode tube for Cell B was prepared using NiO (d_g~ 0.5µm)and GDC(d_g~ 0.2µm) powders using a pore former. The peak power density of these cells were shown to be 203, 400 and 857mW cm^{? 2} for Cell A and 273, 628 and 1017mW cm^{? 2} for Cell B, respectively at 450, 500, and 550°C operating temperature. Both cells showed outstanding performance, and furthermore the anode microstructure of Cell B was shown to be more optimized for better cell performance.     

Stable and high conductivity ceria/bismuth oxide bilayer electrolytes for lower temperature solid oxide fuel cells

A highly conductive bismuth oxide/ceria bilayer electrolyte was developed to reduce solid oxide fuel cell (SOFC) operating temperatures. Bilayer electrolytes were fabricated by depositing a layer of Er_0.2Bi_0.8O_1.5 (ESB) of varying thickness via pulsed laser deposition and dip-coating on a Sm_0.2Ce_0.8O_1.9 (SDC) substrate. The open-circuit potential (OCP) and ionic transference number (t _i) of ESB/SDC electrolytes were tested in a fuel cell arrangement as a function of relative thickness, temperature, and with H₂/H₂O and CO/CO₂ on the anode side and air on the cathode side. These EMF measurements showed a significant increase in OCP and t _i with the bilayer structure, as compared to the cells with a single SDC electrolyte layer. Furthermore, improvement in the OCP and t _i of bilayer SOFCs was observed with increasing relative thickness of the ESB layers. Hence, the bilayer structure overcomes the limited thermodynamic stability of bismuth oxides and prevents electronic conductivity of ceria-based oxides in reducing atmosphere.     

Fe alloying effect on the performance of the Ni anode in hydrogen fuel

Composite materials of YSZ (yttria-stabilized zirconia) with various Ni–Fe alloys were synthesized and evaluated as the solid oxide fuel cell (SOFC) anode using a 200-µm thick YSZ electrolyte as support and YSZ +La_0.8Sr_0.2MnO₃ (LSM) as cathode. The single cell with the YSZ + Ni_0.75Fe_0.25 anode exhibited the highest performance among all the investigated cells, e.g. a peak power density of 403, 337, 218 and 112 mW/cm² was achieved with H₂ fuel at 900, 850, 800 and 750 °C, respectively. The composite anode with the Ni_0.75Fe_0.25 alloy also had the lowest polarization resistance of 0.55 Ω·cm² at 800 °C among all the alloy compositions, indicating that this specific alloy offered a better anode composition than pure Ni. The possible mechanism for the improved performance of Ni with the Fe alloying addition towards H₂ oxidation was discussed.     

Interaction of samaria-doped ceria anode with highly dispersed Ni catalysts in a medium-temperature solid oxide fuel cell during long-term operation

Mixed conducting samaria-doped ceria (SDC) anode with highly dispersed Ni catalysts exhibited a stable high performance over 1100 h in solid oxide fuel cell (SOFC) operated at constant current density of 0.6 A cm^− 2 at 800 °C. While the apparent average size of Ni particles was found to be increased, both the IR-free polarization performance (reflecting an effective reaction area) and the ohmic resistance (reflecting an electronic network) were not changed noticeably during the long-term operation. It was found by scanning electron microscope (SEM) and scanning transmission electron microscope (STEM) that Ni particles were rather stabilized by changing the morphology at the portion contacting with SDC surface presumably due to a strong interaction.     

Influence of sintering temperature and aging on properties of cermet Ni/8YSZ materials obtained by citric method

The anode supported cell for solid oxide fuel cell, as a modification of the traditional Ni-YSZ anode supported on electrolyte, is examined in this work. The materials obtained on the base of citric method are presented and investigated in this work. The materials consisted of 40 wt.% Ni/YSZ, 50 wt.% Ni/YSZ and 60 wt.% Ni/YSZ were obtained. The base Ni/YSZ materials are tested on the two ways: (a) aging tests and (b) sintering tests. All the materials after aging and sintering are tested by the impedance spectroscopy. The results of electrical conductivity for samples before and after aging show that only in the case of 40 wt.% Ni/YSZ, sample loses of metallic conductivity after 500 h of heating. The other samples reveal metallic conductivity even after long period of aging. The tests of sintering temperature show that this process does not affect significantly on electrical conductivity of the materials.     

Effect of deposition temperature on key optoelectronic properties of electrodeposited cuprous oxide thin films

The cuprous oxide (Cu₂O) thin films were electrodeposited with different reaction temperatures. The structural, morphological, optical, photoluminescence and photo response properties of the deposited films were analyzed. XRD analysis reveals cubic crystal structure for the deposited films with polycrystalline nature. The film deposited at room temperature possess high crystallite size of 37 nm. The surface morphology shows that by increasing the deposition temperature pyramid shaped morphology changes. Laser Raman study confirms the peaks 109, 148, 219, 415 and 635 cm^?1 conforms the Cu₂O phase formation. The band gap of the films are 2.02, 2.10 and 2.27 eV for the RT, 40 and 50 °C, respectively. The photoluminescence spectral analysis contains an emission peak at 618 nm confirm the formation of Cu₂O. The photo response study confirms the ohmic nature of the films. The film electrodeposited at room temperature showed good I–V curve at the illumination of 300 W cm^?2.     

Physico-chemical behavior of carbon materials under high temperature and ion irradiation

Carbon/carbon (C/C) composites have been chosen for the conception of the thermal shield of the “Solar Probe” space mission. To understand their behavior under solar aggressions (high temperature and ion irradiation) and know the possible interactions with the shipped-in instruments, these materials are tested in a facility that allows to partially simulate the solar environment and to carry out in situ measurements. The mass loss rate of the materials is recorded and the composition and distribution of the ejected species are followed using an opened source mass spectrometer and a post-treatment XPS analysis of the condensed species on a gold-plated copper target is also performed. Besides this, the sputtering processes of graphite at high temperature and ion irradiation have been theoretically investigated in order to understand the main parameters that can influence the erosion of the material and predict accurately the physico-chemical behavior of the C/C composites.     

CARS temperature measurement in a LOX/CH4 spray flame

Coherent anti‐Stokes Raman scattering (CARS) spectroscopy has been used to investigate cryogenic liquid oxygen/gaseous methane (LOX/CH₄) flames on a medium‐size test facility at a pressure of 0.24 MPa and mass flow of 0.025 kg/s. Single‐shot, broadband CARS spectra with simultaneous detection of the Q‐branches of hydrogen and water molecules were recorded with good signal‐to‐noise ratio. Temperature was deduced from the H₂ and H₂O CARS profiles. The spatial temperature distribution in a comparatively harsh environment has been measured successfully. The measurements took place in the windowed combustion chamber of the DLR M3 test facility, aiming to provide data for validation of rocket combustor modeling. Copyright © 2010 John Wiley & Sons, Ltd.     

Polarization behavior of Ni-YSZ cermet anodes in YSZ fuel cells running on methane under internal reforming conditions

The polarization characteristics of the Ni-YSZ cermet anode/YSZ interface were studied as a function of gas phase composition, temperature and anodic overpotential in methane fuelled internal reforming YSZ fuel cells. AC impedance measurements carried out under open circuit conditions in the temperature range 800 to 900°C showed the presence of at least two rate-limiting processes that were influenced by temperature and gas phase composition. The apparent polarization resistance, R_app, of the Ni-YSZ cermet anode/YSZ interface was found to increase with increasing methane partial pressure and decreasing H₂O partial pressure. The activation energy related to the apparent polarization conductance R _app ⁻¹ varied between 0.7 and 1.1 eV, mainly due to the variation of P_{H 2 O}. The order of magnitude of the apparent capacitance, C_app, values calculated from AC impedance data under open circuit conditions indicate that the observed capacitance corresponds to the double layer capacitance of the Ni/YSZ interface and/or a pseudo-capacitance related to adsorption of species on the Ni-YSZ cermet electrode accompanied by charge transfer. C_app was found to decrease with increasing methane partial pressure. AC impedance measurements carried out under closed circuit conditions at 900 °C and four different P_{H 2 O} showed the appearance of a low-frequency inductive loop at high anodic over-potentials, in addition to the features observed under open circuit conditions. The effect of gas phase composition on R_app was similar to the one observed under open circuit conditions. In addition an almost exponential decrease of R_app with increasing anodic overpotential was observed. The present results are compared with results presented in literature and discussed in the frame of the mechanism of the electrochemical and catalytic reactions taking place over the anode. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Effect of temperature on growth and structure of carbon nanotubes by chemical vapor deposition

The effect of temperature on growth and structure of carbon nanotubes (NTs) using chemical vapor deposition (CVD) has been investigated. Iron embedded silica was used to grow NTs in large quantity at various temperatures from 600 to 1050 °C with gas pressure fixed at 0.6 and 760 Torr, respectively. The growth and structure of the NTs are strongly affected by the temperature. At low gas pressure, the NTs are completely hollow at low temperature and bamboo-like structure at high temperature. While at high gas pressure, all the NTs are bamboo-like structure regardless of temperature. The diameter of NTs increases significantly with temperature. At low gas pressure the diameter gets bigger by mainly increasing the number of graphene layers of the wall of NTs, whereas at high gas pressure the diameter gets bigger by increasing both the number of graphene layers of the wall and the inner diameter of the NTs. This result indicates that the growth temperature is crucial in synthesizing NTs with different structures. The findings here are important for realizing controlled growth of NTs for their applications in different fields. Received: 20 November 2001 / Accepted: 21 November 2001 / Published online: 4 March 2002     

Electronic behavior of carbon clusters/hafnium oxide composite material

An alternating hafnium-O-phenylene hybrid copolymer was calcined under the reduced pressure at 400–700 °C to obtain black-colored materials. XRD and TEM analyses showed that the calcined materials were composed of carbon clusters with the diameters of 20 nm and hafnium oxide particles with the diameters of a few nm. ESR spectral examinations revealed that the calcined materials formed a stable cation radical on the carbon clusters and exhibited an oxidation–reduction function. When Au particles were supported on the material, an efficient oxidation–reduction function was found to appear.     

Optimization of cuprous oxide nanocrystals deposition on multiwalled carbon nanotubes

Cu (I) phenyl acetylide was used as a source of copper to achieve a homogeneous distribution of Cu₂O nanocrystals (10–80 nm) decorated on multiwalled carbon nanotubes (MWCNTs) having an average diameter of 10 nm. Pristine MWCNTs were first oxygen-functionalized by treating them with a mixture of concentrated (H₂SO₄/HNO₃ : 3/1) acids and the products were characterized by X-ray powder diffraction, transmission and scanning electron microscopy, energy dispersive X-ray analysis, X-ray photoelectron spectroscopy and thermogravimetric analysis. An easy, efficient and one-step impregnation method was followed to produce copper-containing nanoparticles on the MWCNTs. The copper-treated MWCNTs dried at room temperature were seen to be well decorated by copper-containing nanoparticles on their outer surface. The MWCNTs were then heat-treated at 400 °C in a nitrogen atmosphere to produce a homogeneous distribution of cuprous oxide nanocrystals on their surface. By varying the ratio of copper to oxygen-functionalized MWCNTs, Cu₂O nanocrystals decorated on MWCNTs with different copper content can be obtained.     

The effect of deposition temperature on the intermixing and microstructure of Fe/Ni thin film

The physical vapour deposition of Ni atoms on α-Fe(001) surface under different deposition temperatures were simulated by molecular dynamics to study the intermixing and microstructure of the interfacial region. The results indicate that Ni atoms hardly penetrate into Fe substrate while Fe atoms easily diffuse into Ni deposition layers. The thickness of the intermixing region is temperature-dependent, with high temperatures yielding larger thicknesses. The deposited layers are mainly composed of amorphous phase due to the abnormal deposition behaviour of Ni and Fe. In the deposited Ni-rich phase, the relatively stable metallic compound B₂ structured FeNi is found under high deposition temperature conditions.     

Diffusion of CO2/CH4 confined in narrow carbon nanotube bundles

ABSTRACT

The diffusion of a CO₂/CH₄ mixture in carbon nanotube (CNT) bundles was studied using molecular simulations. The effect of diameter and temperature on the diffusion of the mixture was investigated. Our results show that the single-file diffusion occurs when CO₂ and CH₄ are confined in CNTs of diameter less than 1.0 nm. In CNTs of diameter larger than 1.0 nm, both molecules diffuse in the Fickian style. The transition from single-file to Fickian diffusion was demonstrated for both CO₂ and CH₄ molecules. A dual diffusion mechanism was observed in the studied (20, 0) CNT bundle, single-file diffusion of CO₂ in the interstitial sites of (20, 0) CNT bundle and Fickian diffusion of CO₂ and CH₄ in the pores. For CO₂, the interaction energies (CO₂–CO₂ and CO₂–CNT) are larger than that of CH₄ in all cases. But only a very small difference in the diffusion coefficient was observed between CO₂ and CH₄. Temperature has a negligible effect on the difference between diffusion coefficients of CO₂ and CH₄ in the studied CNT bundles. The adsorption, diffusion and permeation selectivities are discussed and compared, and the adsorption is demonstrated to be the rate limiting step for the separation of CO₂/CH₄ in CNT bundle membranes.     

变压加载对直接甲醇燃料电池阳极性能的影响（英）

为评价直接甲醇燃料电池（DMFC）阳极的稳定性,利用扫描电化学显微镜和常规电化学技术,研究了变压加载过程中DMFC阳极性能的变化。结果表明,在探针扫描过程中,经不同电压加载后的DMFC阳极表面的扫描电流呈相似的锯齿状分布。当阳极加载2 h,随加载电位升高,扫描峰电流的数量减少,对应峰电流的数值则先增大再减小,表明阳极的催化活性处于不均匀分布状态且随加载时间延长和加载电位升高而逐渐降低。在不同加载电位下,随加载时间延长,循环伏安曲线上的正向和反向电流峰先负移再正移,但抗CO性能持续降低。DMFC阳极在0.6 V下分别加载16 h和72 h后,催化剂粒径由3.4 nm分别增大到3.6 nm和4.4 nm。在0.8 V下加载72 h后,Pt/Ru重量比由2.0增加到3.9。变压加载使催化活性的不均匀分布加剧催化剂粒径长大,Ru流失加快,从而导致阳极催化性能衰减。     

变压加载对直接甲醇燃料电池阳极性能的影响（英）

为评价直接甲醇燃料电池（DMFC）阳极的稳定性,利用扫描电化学显微镜和常规电化学技术,研究了变压加载过程中DMFC阳极性能的变化。结果表明,在探针扫描过程中,经不同电压加载后的DMFC阳极表面的扫描电流呈相似的锯齿状分布。当阳极加载2 h,随加载电位升高,扫描峰电流的数量减少,对应峰电流的数值则先增大再减小,表明阳极的催化活性处于不均匀分布状态且随加载时间延长和加载电位升高而逐渐降低。在不同加载电位下,随加载时间延长,循环伏安曲线上的正向和反向电流峰先负移再正移,但抗CO性能持续降低。DMFC阳极在0.6 V下分别加载16 h和72 h后,催化剂粒径由3.4 nm分别增大到3.6 nm和4.4 nm。在0.8 V下加载72 h后,Pt/Ru重量比由2.0增加到3.9。变压加载使催化活性的不均匀分布加剧催化剂粒径长大,Ru流失加快,从而导致阳极催化性能衰减。     

RAMAN谱研究在退火和镍衬底上金刚石形核中甲烷的影响(英文)

藉助SEM和MICRO RAMAN ,我们研究了在退火和在镍衬底上金刚石形核中甲烷CH4 的影响。CH4 的浓度分别为 0 % ,0 5 % ,1 5 %和 2 5 % ,其中当甲烷浓度为 1 5 %时 ,金刚石在镍衬底上金刚石形核密度为 3× 1 0 8/cm2 ,这个结果高于以前的结果。金刚石膜的质量是好的。     

Laser-induced deposition of Ni lines on ferrite in NiSO4 aqueous solution

Maskless deposition of nickel lines on single crystalline Mn-Zn ferrite (MnO:ZnO:Fe₂O₃=31:17:52) has been investigated in a NiSO₄ aqueous solution by Ar⁺ laser irradiation. A high deposition rate of up to 36.4m/s was achieved by a single scan of laser beam. The purity of deposited nickel layers is up to 86%. In particular, well-defined values of laser power and laser irradiation time were necessary for effective deposition. The deposition process was found to be a thermochemical process.On leave from D. S. Scanner Co., Ltd., 5-3-7. Fukushima, Osaka 553, Japan