Materials Science Forum Vol. 847

Abstract: Microstructure, hydrogen storage properties and thermal stabilities of V-Ti-Fe alloys prepared by arc-melting were studied in this work. It was confirmed that V₆₀Ti₃₀Fe₁₀, V₇₀Ti₂₀Fe₁₀ and V₈₀Ti₁₀Fe₁₀ alloys are a body-centered cubic (bcc) single phase, while V₇₅Ti₁₀Fe₁₅ alloy consists of the bcc main phase and C14-typed Laves secondary phase. Experimental results show that the V₈₀Ti₁₀Fe₁₀ alloy reached the largest hydrogen absorption capacities which were about 1.9 wt.% and 1.62 wt.% at 423 K and 473 K, while V₇₅Ti₁₀Fe₁₅ alloy with C14-typed Laves phase showed better hydrogen desorption capacities with 1.31 wt.% at 423 K and 1.35 wt.% at 473 K, respectively. In addition, the DSC measurements indicate that the thermal stability of V₇₅Ti₁₀Fe₁₅ alloy with C14-typed Laves phase decreased, which is very beneficial to the improvement of dehydrogenation rate in the alloy.

Abstract: A novel sulfur/polypyrrole/graphene nanosheet composite (S/PPy/GNS) was synthesized and investigated as a promising cathode material. This ternary composite was prepared via in situ polymerization of pyrrole monomer with nanosulfur and GNS aqueous suspension followed by heat-treatment. Scanning electronic microscopy observation revealed the formation of a highly porous structure consisting sulfur and polypyrrole coating on the GNS surface. In this composite, GNS works as nanocurrent collector and enhances the conductivity of the composite, and polypyrrole with its high adhesion ability to GNS could act as a binder to connect sulfur and GNS. The resulting S/PPy/GNS composite cathode exhibits high and stable specific discharge capacities of 991 mAh g^-1 after 50 cycles at 0.1 C and good rate capability.

Abstract: Co₃O₄ nanoflakes/N-doped graphene (NG) was synthesized through a facile two-step synthesis route. The phase composition and morphology of the products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDS). It has been found that introduction of NG has effects on the morphology of Co₃O₄ and leads to a well distribution of Co₃O₄ nanoflakes. The electrochemical properties of as-synthesized materials were measured by cyclic voltammetry (CV), galvanostatic charge/discharge tests and electrochemical impedance spectroscopy (EIS). The composite presents an enhanced supercapacitor performance than the pristine Co₃O₄ nanoflakes, mainly due to the strong synergistic effect of the NG and Co₃O₄.

Abstract: The intermetallic alloy LaNi_3.8AlMn_0.2 and its deuteride LaNi_3.8AlMn_0.2D_3.2 were studied by neutron powder diffraction. The experimental results show that the crystal structure of LaNi_3.8AlMn_0.2 is CaCu₅ type with the hexagonal P6/mmm space group, the substituted Al atoms occupy 2c and 3g sites, while Mn atoms are only located on the 3g sites. For the corresponding deuteride LaNi_3.8AlMn_0.2D_3.2, the P6/mmm space group gives the best refinement, but D atoms enter two interstitial sites 6m and 12n.

Abstract: The structures of as-cast LaNi_3.8AlMn_0.2 alloys and subsequent compounds by means of annealing at different temperature (850, 900, 950, 1000 ^oC) were examined by using neutron powder diffraction (NPD) and X-ray diffraction (XRD). Based on the Rietveld method, the diffraction data was refined using FullProf software. The refined results demonstrate the structure types of all compounds are CaCu₅ type and their space groups are P6/mmm. Increasing the annealing temperature, the lattice parameters of LaNi_3.8AlMn_0.2 compounds did not possess clearly linear variation. It is noted that Mn atoms do not occupy the 2c sites but occupy the 3g sites in all compounds.

Abstract: Theoretical capacity of silicon is 4200mAhg^-1, but pure silicon had huge volume change during lithium insertion, which reduces the cycle life of silicon. In this paper, pure silicon was replaced of metallic silicon to relieve volume effect. Metallic silicon contains some alloying elements which improve the conductivity of the electrode material. The elements in metallic silicon will relief the volume change of silicon substrate during lithium insertion/ de-lithiation process. Metallic silicon was treated by mechanical alloying (MA) which is an effective method to reduce particle sizes of metallic silicon. The results show that MA can improve cycle performance of metallic silicon. Metallic silicon treated by MA performs a better cycling performance compared with the unsettled materials and a higher discharge capacity in the first cycle.

Abstract: In situ chemical oxidation polymerization of pyrrole on the surface of sulfur/multi-walled carbon nanotube particle was carried out to synthesize a novel polypyrrole coated sulfur/multi-walled carbon nanotube (PPy@S/MWCNT) composite. The sulfur/multi-walled carbon nanotube composite (S/MWCNT) was prepared by a facile quasi-emulsion template method in an oil/water system. The ternary PPy@S/MWCNT composite was characterized by elemental analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical measurements. In the composite, polypyrrole works as a conducting matrix as well as a coating agent, confining the active materials within the electrode, while the MWCNT creates a highly conductive and mechanically flexible framework, hence enhancing the electronic conductivity and the rate capability of the material. This ternary composite exhibits stable cyclability, retaining a discharge capacity of 612 mAh g^-1 at 0.1 C after 100 cycles. Furthermore, up to 1.5 C rate, the ternary composite still delivered a highly reversible discharge capacity of 463 mAh g^-1.

Abstract: Polyethylene glycol (PEG)/ expanded vermiculite (EVMT) shape-stabilized composite phase change material (ss-CPCM) was prepared by a facile vacuum impregnation method. The maximum mass percentage for PEG retained in ss-CPCM was 75.1 wt.% due to specific non-uniform flat layers pore structure of EVMT. The scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FT-IR) analysis results indicated that the melted PEG was adsorbed on the surface and completely dispersed into the pores of EVMT and no chemical changes took place during the heating and cooling processes. X-ray diffraction (XRD) results showed that the crystal structure of PEG was not destroyed after impregnation whereas the crystallization process of PEG was greatly restrained. Differential scanning calorimetry (DSC) results indicated that ss-CPCM melted at 57.61°C with a latent heat of 103.1 J/g and solidified at 33.19°C with a latent heat of 88.29 J/g. In addition, the thermal conductivity of ss-CPCM reached 0.418W/m K. The ss-CPCM can be considered as promising candidate materials for building applications due to their suitable phase change temperature, large latent heat and excellent chemical compatibility.

Abstract: In this study, an Mg-air battery based on air cathode with different content of Na₂SO₄ was prepared to study the effect of Na₂SO₄ on the performance of Mg-air battery. The electrochemical performance of the air cathode was studied by potentiodynamic polarization and electrochemical impedance spectroscopy. The results indicated that the electrochemical activity of the electrode enhanced with the increasing Na₂SO₄. The discharge performance of the battery was investigated by constant-current discharge test, and the results showed that the discharge potential of the battery also improved with the increasing of Na₂SO₄. However, the forming of air cathode became difficult gradually with the increasing content of Na₂SO₄. What is worse, the oversize pore produced in the moisture barrier when the content of Na₂SO₄ was too high and the moisture barrier would lose resistance to water. So the content of Na₂SO₄ should not be too high.