Preparation and application of gallium-based conductive materials in the very recent years

Gallium and its alloys are a group of metallic materials with low-melting points at or around room temperature.Apart from the good electrical conductivity,the unique liquid state endows those metals with excellent compliance and self-healing capacity,which present great value in the development of flexible and stretchable electronics.Constrained by the high surface tension and low viscosity,however,liquid metals cannot be applied to some common microelectronics manufacturing technologies such as micro-electro mechanics in the preceding years,which impedes their mass production in electronic devices.To address these issues and broaden the applications of liquid metals in electronics devices,numerous efforts have been taken and great progress has been made especially in the very recent years.This review summaries the recent development of liquid metal-based conductive materials from the aspects of preparation or modification methods and their accommodative fabrication techniques in flexible electronic applications.Further outlook including expectations and challenges of liquid metal-based conductive materials are also presented.

Direct ink writing of conductive materials for emerging energy storage systems

Direct ink writing(DIW)has recently emerged as an appealing method for designing and fabricating three-dimensional(3D)objects.Complex 3D structures can be built layer-by-layer via digitally controlled extrusion and deposition of aqueous-based colloidal pastes.The formulation of well-dispersed suspensions with specific rheological behaviors is a prerequisite for the use of this route.In this review article,the fundamental concepts of DIW are presented,including the operation principles and basic features.Typical strategies used for ink formulation are discussed with a focus on the most widely used electrode materials,including graphene,Mxenes,and carbon nanotubes.The recent progress in printing design of emerging energy storage systems,encompassing rechargeable batteries,supercapacitors,and hybrid capacitors,is summarized.Challenges and future perspectives are also covered to provide guidance for the future development of DIW.

Enhanced light extraction of GaN-based light-emitting diodes with periodic textured SiO_2 on Al-doped ZnO transparent conductive layer

We report an effective enhancement in light extraction of Ga N-based light-emitting diodes（LEDs） with an Al-doped Zn O（AZO） transparent conductive layer by incorporating a top regular textured SiO2 layer. The 2 inch transparent throughpore anodic aluminum oxide（AAO） membrane was fabricated and used as the etching mask. The periodic pore with a pitch of about 410 nm was successfully transferred to the surface of the SiO2 layer without any etching damages to the AZO layer and the electrodes. The light output power was enhanced by 19% at 20 m A and 56% at 100 m A compared to that of the planar LEDs without a patterned surface. This approach offers a technique to fabricate a low-cost and large-area regular pattern on the LED chip for achieving enhanced light extraction without an obvious increase of the forward voltage.

Hybrid graded element model for transient heat conduction in functionally graded materials

This paper presents a hybrid graded element model for the transient heat conduction problem in functionally graded materials （FGMs）. First, a Laplace transform approach is used to handle the time variable. Then, a fundamental solution in Laplace space for FGMs is constructed. Next, a hybrid graded element is formulated based on the obtained fundamental solution and a frame field. As a result, the graded properties of FGMs are naturally reflected by using the fundamental solution to interpolate the intra-element field. Further, Stefest＇s algorithm is employed to convert the results in Laplace space back into the time-space domain. Finally, the performance of the proposed method is assessed by several benchmark examples. The results demonstrate well the efficiency and accuracy of the proposed method.

Uncover the Aesthetic Simplicity Associated with Mass Transfer in Energy Materials

Aesthetics,referred frequently to as a philosophical term,has played a starring role in forming and evolving a number of aspects of human society,including arts,politics,economics,ethics,etc.Indeed,exploring and investigating the aesthetic phenomena in the scientific field have aroused insightful research findings,which in turn has stimulated research interests in such a science-aesthetics field.In particular,better-evaluated aesthetic aspects of the materials field are expected to be uncovered upon the exceedingly-exposed fundamental breakthroughs in researching the basic structure and functionality of materials.In this report,we glimpse into the aesthetic simplicity of energy materials and comprehend specifically the mass transfer functionalities of key categories of energy materials through an intuitive and bottom-up approach.Our effort aspires to shed new lights on the functionality understanding and manipulation of functional materials in general.

STUDY ON THE STRUCTURE, ELECTRICAL PROPERTIES AND CONDUCTION MECHANISM 0F THE MULTICRYSTAL MULTIPHASE MATERIAL Li_2MO_2-xWxO_6

The conductivity of non-crystalline fast ionic conductor for B_2O_3-Li_2O-LiCl-Al_2O_3 system is studiedin this paper. The glass structure of this system is discussed by means of infrared spectrum and X-ray fluorescence analysis, and the effects of LiCl and A1_2O_3 on the conductivity of Li^+ in the system are studied as well. Adding Li_2O to the system gives rise to transfer from [BO_3] triangular units to [BO_4] tetrahedral. When Li_2O content exceeds 30mol%, the main group of the glass is the diborate group with more [BO_4] tetrahedra. The adding of LiCl has no obvious influence on the glass structure, and LiCl is under a state dissociated by network, but with the increase of LiCl, the increase of conductivity is obvious. By adding A1_2O_3, the glass can be formed when the room-temperature is cooling down,the conductivity decreases while the conductive activatory energy increases for the glass. The experiment shows that conductivity in the room-temperature is σ= 6.2×10^(-6)Ω^(-1)cm^(-1), when at 300℃, the σ=6.8×10^(-3)Ω^(-1)cm^(-1). The conductive activatory energy computed is 0.6～1.0eV.

Copper Ions Removal from Wastewater by Electrocoagulation Using Cement-based Cathode Plates

The present work uses PEO solution to well disperse carbon fiber and identifies percolation thresholds of carbon fiber and carbon black which are used as conductive fillers.The resultant cathode plates have an average compressive strength of 27.3 MPa and flexural strength of 29.09 MPa,which demonstrate excellent mechanical properties.The Cu^(2+)removal efficiency was measured at different current densities in EC process with cement-based cathode plate,while the voltage changes were recorded.The results showed that the cement-based cathode plate operated stably and achieved 99.7%removal of 1 L of simulated wastewater with a Cu^(2+)concentration of 200 ppm at a current density of 8 m A/cm^(2)for 1 h.Characterization of floc and tested cathode plates,SEM and EDS analyses,and repeatability testing of the tested plates demonstrate the reusability of the plates,proving that cement-based plates can effectively replace metal cathode plates,reduce the cost of EC and improve the applicability of EC devices.

Functionalized Fiber-Based Strain Sensors:Pathway to Next-Generation Wearable Electronics

Wearable strain sensors are arousing increasing research interests in recent years on account of their potentials in motion detection,personal and public healthcare,future entertainment,man-machine interaction,artificial intelligence,and so forth.Much research has focused on fiber-based sensors due to the appealing performance of fibers,including processing flexibility,wearing comfortability,outstanding lifetime and serviceability,low-cost and large-scale capacity.Herein,we review the latest advances in functionalization and device fabrication of fiber materials toward applications in fiber-based wearable strain sensors.We describe the approaches for preparing conductive fibers such as spinning,surface modification,and structural transformation.We also introduce the fabrication and sensing mechanisms of state-of-the-art sensors and analyze their merits and demerits.The applications toward motion detection,healthcare,man-machine interaction,future entertainment,and multifunctional sensing are summarized with typical examples.We finally critically analyze tough challenges and future remarks of fiber-based strain sensors,aiming to implement them in real applications.

Reciprocity principle-based model for shielding effectiveness prediction of a rectangular cavity with a covered aperture

According to the reciprocity principle, we propose an efficient model to compute the shielding effectiveness of a rectangular cavity with apertures covered by conductive sheet against an external incident electromagnetic wave. This problem is converted into another problem of solving the electromagnetic field leakage from the cavity when the cavity is excited by an electric dipole placed within it. By the combination of the unperturbed cavity field and the transfer impedance of the sheet, the tangential electric field distribution on the outer surface of the sheet is obtained. Then, the field distribution is regarded as an equivalent surface magnetic current source responsible for the leakage field. The validation of this model is verified by a comparison with the circuital model and the full-wave simulations. This time-saving model can deal with arbitrary aperture shape, various wave propagation and polarization directions, and the near-field effect.

SYNTHESIS AND IDENTIFICATION OF CONDUCTING POLYANILINE DOPED WITH RARE EARTH CHLORIDE

Polyaniline doped with rare earth chloride was synthesized in organic solvent and identified by elemental analysis and infrared spectroscopy. The experimental results show that there exists both doping and complexation at the same time in the resulting product. When pH4. Moreover, polyaniline doped with rare earth chloride exhibits better thermal stability than that doped with hydrochloric acid.

Charge transport in conducting polyaniline co-doped with sulfosalicylic acid and dodecylbenzoyl sulfonic acid

We prepared conducting polyaniline （PAn） co-doped with sulfosalicylic acid （SSA） and dodecylbenzoyl sultonic acid （DBSA） in micro-emulsive polymerization, and studied its charge transport behaviors based on the measurement of its electrical conductivity in the temperature range between 203 K and 298 K. The conductivity was found to increase with temperature, similar to the case in semiconductors. Analyzing the experimental data with three models, namely the charge-energy-limitedtunneling model, Kivelson model and the three-dimensional variable range hopping （3D-VRH） model demonstrated that these models all describe well the charge transport behaviors of PAn co-doped with SSA and DBSA within the mentioned temperature range. From calculation with the 3D-VRH model, the hopping distance of the conducting PAn is obviously larger than its localization length. The PAn doped with SSA and DBSA enjoys desirable crystallinity due to the co-doping of two functional sulfonic acids. The macroscopic conductivity may correspond to three-dimensional transport in the network of the bundles, and the metallic islands may be attributed to quasi-one-dimensional bundles.

Structure and properties of NASICON synthesized by two different zirconium salts

ZrOCl2·8H2O and ZrO（NO3）2·2H2O were used respectively to synthesize a NASICON solid electrolyte by a sol-gel method. The structure and properties of two samples were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and electro-chemical impedance spectroscopy （EIS）. The crystal structure was investigated by the Rietveld refinement. It is found that both the samples contain a monoclinic C2/c phase as the main conductive phase with the lattice parameters ofa=1.56312 nm, b=0.90784 nm and c=0.92203 nm, though a small amount of rhombohedral phase is also detected in the final product. The sample synthesized by ZrO（NO3）2·2H/O contains more monoclinic phase （89.48wt%） than that synthesized by ZrOCl2·SH2O（74.91 wt%）. As expected, the ionic conductivity of the latter is higher than that of the former; however, the activation energy of the latter （0.37 eV） is slightly higher than that of the former （0.35 eV）.

Influence of graphite particle size and its shape on performance of carbon composite bipolar plate

Bipolar plates for proton exchange membrane fuel cell (PEMFC) where polymer is used as binder and graphite is used as electric filler were prepared by means of compression molding technology. Study on the effects of graphite particle size and shape on the bipolar plate performance, such as electrical conductivity, strength, etc. showed that with decrease of graphite particle size, bulk electrical conductivity and thermometric conductivity decreased, but that flexural strength was enhanced. After spherical graphite occurrence in flake-like form, the flexural strength of the bipolar plate was enhanced, electrical conductivity increased but thermal conductivity decreased in direction paralleling pressure direction, and both electrical conductivity and thermometric conductivity reduced in direction perpendicular to pressure direction.

A meshless model for transient heat conduction analyses of 3D axisymmetric functionally graded solids

A meshless numerical model is developed for analyzing transient heat conductions in three-dimensional （3D） axisymmetric continuously nonhomogeneous functionally graded materials （FGMs）. Axial symmetry of geometry and boundary conditions reduces the original 3D initial-boundary value problem into a two-dimensional （2D） problem. Local weak forms are derived for small polygonal sub-domains which surround nodal points distributed over the cross section. In order to simplify the treatment of the essential boundary conditions, spatial variations of the temperature and heat flux at discrete time instants are interpolated by the natural neighbor interpolation. Moreover, the using of three-node triangular finite element method （FEM） shape functions as test functions reduces the orders of integrands involved in domain integrals. The semi-discrete heat conduction equation is solved numerically with the traditional two-point difference technique in the time domain. Two numerical examples are investigated and excellent results are obtained, demonstrating the potential application of the proposed approach.

Interlayer transport of an electron in bilayer graphene with phonon-induced lattice distortion in the presence of biased potential

The interlayer transport of an electron in bilayer graphene influenced by a phonon in the presence of a biased potential is investigated using the tight-binding approach. The in-plane optical mode E2g and out-of-plane optical mode B1g associated with the applied biased potential are considered to compute and discuss the interlayer transport probability of an electron initially localized on the bottom layer at the Dirac point in the Brillouin zone. Without the biased potential, the interlayer transport probability is equal to 0.5 regardless of the phonon displacement except for a few special cases. Applying a biased potential to the layers, we find that in different phonon modes the function of the transport probability with respect to the applied biased potential and phonon displacement is complex and various, but on the whole the transport probability decreases with the increase in the absolute value of the applied biased potential. These phenomena are discussed in detail in this paper.

Flexible and Stretchable Electrodes for In Vivo Electrophysiological and Electrochemical Monitoring

In vivo monitoring of bioelectrical and biochemical signals with implanted electrodes has received great interest over the past decades.However,this faces huge challenges because of the severe mechanical mismatch between conventional rigid electrodes and soft biological tissues.In recent years,the emergence of flexible and stretchable electrodes offers seamless and conformable biological-electronic interfaces and has demonstrated significant advantages for in vivo electrochemical and electrophysiological monitoring.This review first summarizes the strategies for electrode fabrication from the point of substrate and conductive materials.Next,recent progress in electrode functionalization for improved performance is presented.Then,the advances of flexible and stretchable electrodes in exploring bioelectrical and biochemical signals are introduced.Finally,we present some challenges and perspectives ranging from electrode fabrication to application.

Skin-Inspired Electronics Enabled by Supramolecular Polymeric Materials

Next-generation electronics that intimately interact with the human body would play crucial roles in future health monitors and early disease diagnosis.Skin-inspired electronics have been rapidly growing in the past decade to emulate the remarkable sensory and responsive nature of the human skin tissue.

Recent Progress in All-Solution-Processed Organic Solar Cells

All-solution-processed organic solar cells(OSCs)(from the bottom electrode to the top electrode)are highly attractive thanks to their low cost,lightweight and high-throughput production.However,achieving highly efficient all-solution-processed OSCs remains a significant challenge.One of the key issues is the lack of high-quality solution-processed electrode systems that can replace indium tin oxide(ITO)and vacuum-deposited metal electrodes.In this paper,we comprehensively review recent advances in all-solution-processed osCs,and classified the devices as the top electrode materials,including silver nanowires(AgNWs),conducting polymers and composite conducting materials.The correlation between electrode materials,properties of electrodes,and device performance in all-solution-processed OSCs is elucidated.In addition,the critical roles of the active layer and interface layer are also discussed.Finally,the prospects and challenges of all-solution-processed OSCs are presented.

A review on structures,materials and applications of stretchable electrodes

With the rapid development of wearable smart devices,many researchershave carried out in-depth research on the stretchable electrodes.As one of the corecomponents for electronics,the electrode mainly transfers the electrons,which plays animportant role in driving the various electrical devices.The key to the research for thestretchable electrode is to maintain the excellent electrical properties or exhibit theregular conductive change when subjected to large tensile deformation.This articleoutlines the recent progress of stretchable electrodes and gives a comprehensiveintroduction to the structures,materials,and applications,including supercapacitors,lithium-ion batteries,organic light-emitting diodes,smart sensors,and heaters.Theperformance comparison of various stretchable electrodes was proposed to clearly showthe development challenges in this field.We hope that it can provide a meaningfulreference for realizing more sensitive,smart,and low-cost wearable electrical devices inthe near future.

Carbonate-salt-based composite materials for medium- and high-temperature thermal energy storage

This paper discusses composite materials based on inorganic salts for medium- and high-temperature thermal energy storage application. The composites consist of a phase change material （PCM）, a ceramic material, and a high thermal conductivity material. The ceramic material forms a microstructural skeleton for encapsulation of the PCM and structural stability of the composites; the high thermal conductivity material enhances the overall thermal conductivity of the composites. Using a eutectic salt of lithium and sodium carbonates as the PCM, magnesium oxide as the ceramic skeleton, and either graphite flakes or carbon nanotubes as the thermal conductivity enhancer, we produced composites with good physical and chemical stability and high thermal conductivity. We found that the wettability of the molten salt on the ceramic and carbon materials significantly affects the microstructure of the composites.