Structures and electrochemical hydrogen storage performance of Si added A_2B_7-type alloy electrodes

In order to ameliorate the electrochemical hydrogen storage performance of La-Mg-Ni system A2B7-type electrode alloys, a small amount of Si was added. The La0.8Mg0.2Ni3.3Co0.2Six （x=0-0.2） electrode alloys were prepared by casting and annealing. The effects of adding Si on the structure and electrochemical hydrogen storage characteristics of the alloys were investigated systematically. The results indicate that the as-cast and annealed alloys hold multiple structures, involving two major phases of （La, Mg）2Ni7 with a Ce2Ni7-type hexagonal structure and LaNi5 with a CaCu5-type hexagonal structure as well as one residual phase LaNi3. The addition of Si results in a decrease in （La, Mg）2Ni7 phase and an increase in LaNi5 phase without changing the phase structure of the alloys. What is more, it brings on an obvious effect on electrochemical hydrogen storage characteristics of the alloys. The discharge capacities of the as-cast and annealed alloys decline with the increase of Si content, but their cycle stabilities clearly grow under the same condition. Furthermore, the measurements of the high rate discharge ability, the limiting current density, hydrogen diffusion coefficient as well as electrochemical impedance spectra all indicate that the electrochemical kinetic properties of the electrode alloys first increase and then decrease with the rising of Si content.

Spin Polarization at Organic-Ferromagnetic Interface： Effect of Contact Configuration

Based on ab initio theory, the interracial spin polarization of a benzene-dithiolate molecule vertically adsorbed on a nickel surface is investigated by adopting different microscopic con- tact configurations. The results demonstrate a strong dependence of the interfacial spin polarization on the contact configuration, where the sign of spin polarization may vary from positive to negative with the change of contact configuration. By analyzing the projected density of states, an interracial orbital hybridization between the 3d orbital of the nickel atom and the sp3 hybridized orbital of the sulfur atom is observed. We also simulated the interracial adsorption in mechanically controllable break junction experiments. The magne- toresistance obtained from Julliere model is about 27% based on the calculated interracial spin polarization, which is consistent with experimental measurement.

Evaluation of hollow fiber T-type zeolite membrane modules for ethanol dehydration

This work presents the design of hollow fiber T-type zeolite membrane modules with different geometric configurations. The module performances were evaluated by pervaporation dehydration of ethanol/water mixtures. Strong concentration polarization was found for the modules with big membrane bundles. The concentration polarization was enhanced at high temperature due to the higher water permeation flux. The increase of feed flow could improve water permeation flux for the membrane modules with small membrane bundle.Computational fluid dynamics was used to visualize the flow field distribution inside of the modules with different configurations. The membrane module with seven bundles exhibited highest separation efficiency due to the uniform distribution of flow rate. The packing density could be 10 times higher than that of the tubular membrane module. The hollow fiber membrane module exhibited good stability for ethanol dehydration.

高熵铁电体研究进展

铁电材料因其换能、储能等功能性而被广泛应用于各类电子功能材料和器件,这主要取决于铁电材料晶体结构基因——极化构型。传统构建相界策略对极化构型调控不够灵活,性能增幅有限,已越来越无法满足器件微型化和集成化的需求。近期,研究者将高熵策略引入到铁电化合物中并系统研究了其对局域极化构型的调控机制。结果表明,在保留传统高熵效应的同时,高熵策略还可充分发挥原子铁电活性、半径等综合因素用于铁电功能基元(局域极化构型与氧八面体倾斜)的定向设计,有效提升外场响应的灵活度,进而大幅度提升铁电化合物的相关电学性能。该类兼具高化学无序度和高铁电功能基元无序度的材料称之为“高熵铁电体”。采用高熵策略在铁电体中开展了一系列研究工作,研究者们分别设计出高熵压电、高熵电致伸缩、高熵储能等材料。本文通过总结高熵铁电体方面的研究工作,将高熵铁电体的发展历程、设计策略、性能优化、结构机理进行梳理,以期为设计下一代高性能铁电材料提供指导。

Composite Eshelby model and domain band geometries of ferroelectric ceramics

A method of composite Eshelby inclusion is proposed for aferroelectric grain with domain switching embedded in a polycrystalline ferroelectric matrix. The method quantifies the twinning structure due to spontaneous polarization, as well as the conventional and non-conventional domain structures after poling induced domain reorientation of 90 degree. The predicted parameters include the volume fraction, the thickness, and the surface inclination angle of switched domain plates. The domain wall energy for non-conventional domain structures is derived in terms of the arrays of misfit dislocations. The domain geometries predicted by the present work agree with the measured domain morphology near an indentation crack tip when subjected to lateral electric field.