Synthesis and characterization of lithium-carbon compounds for hydrogen storage

Three carbon materials were prepared for the synthesis of Li-C compounds, such as Li intercalated graphite. The materials were as-received high purity polycrystalline graphite (G), graphite milled under a hydrogen atmosphere (HG), and graphite milled an argon atmosphere (AG). With respect to the difference for them, HG preserved a better crystalline structure than AG. Each material was milled with Li, where the products are denoted as Li-G, Li-HG, and Li-AG. In XRD patterns of Li-G and Li-HG, the peaks corresponding to LiC₆ and LiC₁₂ were revealed, while no peaks were observed in the case of Li-AG. However, the formation of lithium carbide Li₂C₂ was suggested for Li-AG by a thermal analysis under an inert gas. After the hydrogenation, LiH was formed for all the compounds, and graphite was recovered for Li-G and Li-HG. Each hydrogenated compound desorbed H₂ with different profile by heating up to 500 °C. As a reaction product, Li₂C₂ was formed for the hydrogenated Li-HG and Li-AG. In the case of the hydrogenated Li-G with better crystalline structure, Li intercalated graphite were formed after the dehydrogenation. Therefore, it is concluded that the hydrogen absorption and desorption process of Li intercalated graphite was different from those of Li₂C₂.     

Characterisation of corrosion and wear behaviour of nanoscaled e-beam PVD CrN coatings

The present paper analyses the performance of CrN single-layers produced by electron beam PAPVD (EBPAPVD), finding that both corrosion and wear resistance are directly dependant on the structure and stoichiometry of the nitride. The nanolayer structure of the coatings is formed by periodically varying the nitrogen pressure during deposition resulting in layers with higher and lower N-content. This fact, which has not been described in the literature, causes different structure and morphology of the individual films providing excellent properties to the coating. For corrosion resistance, the CrN layer's greater compactness impedes penetration of the electrolyte and thus prevents the formation of a galvanic couple between the coating and the substrate. Moreover, a good wear resistance is obtained, retarding its delamination.     

Characterization and evaluation of La0.8 Sr0.2Co0.8 Ni0.2O3-δ prepared by a polymer-assisted combustion synthesis as a cathode material for intermediate temperature solid oxide fuel cells

A modified polymer-assisted combustion synthesis method is developed for preparation of La_0.8Sr_0.2Co_0.8Ni_0.2O_3-δ (LSCN) nano-sized cathode particles by using organic additives (glucose and acrylamide) and metal nitrates. The effect of the organic additives, pH value of starting solution and calcination temperature on the formation of the LSCN perovskite phase and microstructure of the powders is investigated. Chemical compatibility between the LSCN and Y₂O₃ stabilized ZrO₂ (YSZ) and Gd₂O₃ doped CeO₂ (GDC) is evaluated and electrochemical activity of LSCN cathode is evaluated. The prepared LSCN is chemically compatible with the YSZ only at temperatures below 850 °C. The electrode area specific resistance (ASR) is 0.30 and 0.10 Ω cm² at 700 and 750 °C, respectively. These results suggest that such prepared LSCN is a promising alternative cathode material for intermediate temperature SOFCs.     

High performance metal-supported intermediate temperature solid oxide fuel cells fabricated by atmospheric plasma spraying

The LSGM(La_0.8Sr_0.2Ga_0.8Mg_0.2O₃) electrolyte based intermediate temperature solid oxide fuel cells (ITSOFCs) supported by porous nickel substrates with different permeabilities are prepared by plasma spray technology for performance studies. The cell having a porous nickel substrate with a permeability of 3.4 Darcy, an LSCM(La_0.75Sr_0.25Cr_0.5Mn_0.5O₃) interlayer on the nickel substrate, a nano-structured LDC(Ce_0.55La_0.45O₂)/Ni anode functional layer, an LDC interlayer, an LSGM/LSCF(La_0.58Sr_0.4Co_0.2Fe_0.8O₃) cathode interlayer and an LSCF cathode current collector layer shows remarkable electric output power densities such as 1270 mW cm⁻² (800 °C), 978 mW cm⁻² (750 °C) and 702 mW cm⁻² (700 °C) at 0.6 V cell voltage under 335 ml min⁻¹ H₂ and 670 ml min⁻¹ air flow rates. SEM, TEM, EDX, AC impedance, voltage and power data with related analyses are presented here to support this high performance. The durability test of the cell with the best power performance shows a degradation rate of about 3% kh⁻¹ at the test conditions of 400 mA cm⁻² constant current density and 700 °C. Results demonstrate the success of APS technology for fabricating high performance metal-supported and LSGM based ITSOFCs.     

SiC纳米陶瓷粉末的激光烧结初探

在纳米材料的成型领域引入选择性激光烧结 ,进行了SiC纳米粉末材料的激光烧结实验 ,采用x射线衍射、SEM等手段对烧结制件的物相、微观组织等进行了分析。在此基础上 ,系统研究了各烧结参数对成型工艺的影响 ,提出了针对烧结不良现象的工艺措施 ,为纳米粉末陶瓷材料的自由成型提供了依据。研究表明 ,采用合理的工艺参数 ,通过选择性激光烧结可以实现SiC纳米陶瓷材料的自由成型 ,烧结制件材料晶粒有所长大 ,但仍保持纳米结构。成型过程中 ,部分粉末材料分解 ,分解产物也保持纳米结构。     

Preparation and electrochemical property of three-phase gas-diffusion oxygen electrodes for metal air battery

Three-phase gas-diffusion oxygen electrodes for metal air battery were prepared and characterized. Nano-structured γ-MnO₂ catalysts were synthesized by solid state redox reaction of two compounds, Mn(CH₃COO)₂·4H₂O and C₂H₂O₄·2H₂O. Their crystal phase, morphologies and particle size were characterized by XRD, TEM, respectively. The electrochemical property of three-phase gas-diffusion oxygen electrodes composed of nano-structured γ-MnO₂ catalysts for oxygen reduction was examined by using the linear polarization method in a neutral solution. Besides, the surface morphologies of the catalytic layer of three-phase gas-diffusion oxygen electrodes were also investigated by SEM. Experimental results revealed that these kinds of three-phase gas-diffusion oxygen electrodes have excellent electrochemical performance. The optimal proportion of nano-structured γ-MnO₂ catalysts in the catalytic layer was 60 wt.%. Three-phase gas-diffusion oxygen electrodes composed with nano-structured γ-MnO₂ catalysts appear to be a highly possible candidate for applications in neutral solution metal air battery.     

Effect of molten V2O5 salt on the corrosion behavior of micro- and nano-structured thermal sprayed SYSZ and YSZ coatings

The corrosion resistance of micro-and nano-structured scandia and yttria codoped zirconia (nano-4 mol%SYSZ and micro-8.6SYSZ) and yttria doped zirconia (4YSZ) in the presence of molten vanadium oxide were investigated. To this end, duplex TBCs (thermal barrier coatings), composed of a bond coat (NiCrAlY) and a top coat (4SYSZ or 4YSZ), were deposited on the IN738LC Ni-based supper-alloy by atmospheric plasma spraying (APS). The corrosion studies of plasma sprayed TBCs were conducted in 25 mg V₂O₅ molten salt at 910 °C for different times. The nanostructured coating, as compared to its micro-structured counterpart, in spite of a further reaction with the V₂O₅ salt, showed a higher degradation resistance during the corrosion test due to increased compliance capabilities resulting from the presence of an extra source of porosity associated with the nano-zones. Finally, the corrosion resistance and degradation mechanism of SYSZ and YSZ coatings were compared with the presence of molten NaVO₃ and V₂O₅ salt, respectively.     

Preparation and characterization of Ge epitaxially grown on nano-structured periodic Si pillars and bars on Si(001) substrate

The selective epitaxial growth of germanium on nano-structured periodic silicon pillars and bars with 360 nm periodicity on Si(001) substrate is studied to evaluate the applicability of nano-heteroepitaxy on the Ge-Si system for different fields of application. It is found that SiO₂ used as masking material plays the key role to influence the strain situation in the Si nano-islands. To analyze this in detail, X-ray diffraction techniques in combination with theoretical simulations based on the kinematical X-ray scattering from laterally strained nano-structures and finite element method (FEM) calculations of the strain field are applied. The oxide related strain in the Si scales about linearly with the thickness of the SiO₂ mask, but FEM simulations supposing a homogeneous stress distribution in the oxide are not sufficient to describe the local strain distribution in the nano-structures. It is demonstrated that the Ge lattice relaxes completely during growth on the Si nano-islands by generation of misfit dislocations at the interface, but a high structural quality of Ge can be achieved by suited growth conditions.     

Nanoscale and nano-structured electrodes of solid oxide fuel cells by infiltration: Advances and challenges

Solid oxide fuel cells (SOFCs) are the most efficient devices for the direct conversion of the chemical energy stored in fuels such as hydrogen and hydrocarbons into electricity. The development of highly efficient and robust SOFCs requires cathodes and anodes with high electrocatalytic activity for O₂ reduction and direct oxidation of hydrocarbon fuels, respectively. Nanoscale engineering of electrode structures via metal salt solution impregnation or infiltration attracts increasing attention as the most effective way to develop highly active and advanced electrode structures for SOFCs. The infiltration method opens a new horizon in the advanced electrode development as the method expands the set of variable electrode materials combinations with the elimination of thermal expansion mismatch and the suppression of potential detrimental reactions between electrode and electrolyte materials. In this article, the advances and challenges in the development of nanoscale and nano-structured electrodes and the fundamental understanding of the remarkable enhancement in the electrode performance are reviewed and discussed with primary focus on the progress and status of the field in the last 5 years.     

Mixing of carbon nanotubes (CNTs) and aluminum powder for powder metallurgy use

In recent years, carbon nanotubes (CNTs) reinforced aluminum matrix composites (AMCs) have attracted increasing attention. The quality of dispersion, however, is a crucial factor which determines the homogeneity and final mechanical properties of these composites. This work studied the mechanical mixing methods, viz. high energy and low energy ball millings, and compared them to a novel polyester binder-assisted (PBA) mixing method. Experimental results showed that the high energy and low energy ball-milled CNTs disintegrated and there were residual stresses, unlike the PBA-CNTs. The CNT dispersion conditions by these three methods were discussed. The Al-CNTs mixture was subsequently consolidated by powder metallurgy (PM) technique. Small addition of CNTs (0.5 wt.%) evidently improved the tensile strength and hardness of the composite by comparing with the pure matrix. Mechanical property enhancements of the Al-0.5CNT composites from PBA and high energy ball milling were superior to that mixed by low energy ball milling. This showed good dispersion effect in PBA and high energy ball milling technique.