Microstructure optimization and electrochemical behavior of in-situ growth Ramsdellite-MnO_(2)@NCA-LDH@CC for supercapacitors and oxygen evolution reaction catalysts

Supercapacitors are electrochemical energy storage devices with great potential applications.Mean-while,the oxygen evolution reaction(OER)determines the efficiency of some electrochemical energy conversions.This study aims at constructing,exploring,and optimizing Ramsdellite-MnO_(2)@NiCoAl-LDH@CC(R-MNCA@CC)composites.The effect of microstructure and Al role on the performance is investigated when R-MNCA@CC was used as supercapacitor electrode material and OER catalyst.Coral-like R-MNCA@CC in-situ growth composites were synthesized by a two-step hydrothermal method.R-MNCA@CC-2(molar ratio of Ni:Co:Al is 1:1:1)performs the best with the largest specific capacitance,1,742 F/g at 1 A/g,increased by 797%and 1,489%compared to that of NiCoAl-LDH and Ramsdellite-MnO_(2).The capacitance retention rate of the R-MNCA@CC-2//AC@CC supercapacitor is 80.1%after 5,000 cycles at 0.8 A/g.The overpotential for driving an OER to reach 10 m/cm^(2)is only 276 mV,which is lower than that of commercial IrO_(2)(300 mV).Noteworthy,we propose a view that is“competing to trigger redox re-action”of electrochemical active sites in LDH during electrochemical processes derived from a discrepancy between theory and experimental results.

A modified model for concurrent topology optimization of structures and materials

This paper presents a study on the concur- rent topology optimization of a structure and its material microstructure. A modified optimization model is proposed by introducing microstructure orientation angles as a new type of design variable. The new model is based on the assumptions that a structure is made of a material with the same microstructure, and the material may have a different orientation within the design domain of the structure. The homogenization theory is applied to link the material and structure scales. An additional post-processing technique is developed for modifying the obtained design to avoid local optima caused by the use of orientation angle variables. Numerical examples are presented to illustrate the viabil- ity and effectiveness of the proposed model. It is found that significant improvement in structural performance can be achieved by optimizing the orientation of microstructures in concurrent topology optimization of structures and materials.

Dynamic mechanical characterization and optimization of particle-reinforced W-Ni-Fe composites

A visco-plastic rate-dependent homogenization theory for particle-reinforced composites was derived and the equivalent elastic constants and the equivalent visco-plastic parameters of these composites were obtained. A framework of homogenization the- ory for particle-reinforced W-Ni-Fe composites, a kind of tungsten alloy, was established. Based on the homogenization theory and a fixed-point iteration method, a unit cell model with typical microstructnres of the composite was established by using dynamic analysis program. The effects of tungsten content, tungsten particle shape and particle size and interface strength on the mechanical properties and the crack propagation of the W-Ni-Fe composite are analyzed under quasi-static and dynamic loadings. The stress-strain curves of the composite are given and the relation between the macro-mechanical characteristics and the microstructure parameters is explored, which provides an important theoretical basis for the optimization of the W-Ni-Fe composites.