With the rapid development of portable and wearable electronic devices, research on flexible energy storage devices has gradually shifted to the directions of miniaturization, softness and intelligence. At the same time, people have higher requirements for the energy density, power density and mechanical properties of the device. As the core part of flexible energy storage devices, electrode material is the key to determining device performance. With the development of flexible energy storage electronic devices, there is an urgent need for new battery technology and fast, low cost and precise control of their microstructure preparation methods. Therefore, the research and development of new energy storage devices such as flexible lithium/sodium-ion batteries, flexible lithium-sulfur batteries, and flexible zinc-air batteries have become the current research hotspots in academia. The current research status of flexible energy storage battery electrodes in recent years was discussed in this paper, the design of flexible electrode materials (independent flexible electrodes and flexible substrate electrodes), and the preparation process of flexible electrode materials of different dimensions (one-dimensional materials, two-dimensional materials and three-dimensional materials) and applications of flexible energy storage electrodes (flexible lithium/sodium ion batteries, flexible lithium-sulfur batteries, flexible zinc-air batteries) were compared and analyzed, and the structural characteristics and electrochemical properties of electrode materials were discussed. Finally, the current problems faced by flexible energy storage devices were pointed out, and the future focus of flexible energy storage devices was the research and development of new solid electrolytes, the rational design of device structures and the continuous optimization of packaging technology.
Because of its light weight, flexibility, and good contact with electrode, solid polymer electrolyte (SPE) has become a potential material for the development of electrochemical devices with high energy density, high safety and high flexibility, and has been paid extensive attention in recent years. However, defects such as low ionic conductivity and poor mechanical properties have also become the problems that limit its further commercialization. It is possible to solve these problems by forming a composite system of polymers by means of crosslinking, blending, copolymerization, etc. Therefore, in this paper, the mechanism of ionic conductivity in polymers was briefly introduced in order to explain the strategies to solve the above problems from the point of principle. Then, the applications and modification strategies of a variety of polymer-based composite electrolytes in electrochemical devices in recent years were reviewed. Finally, the problems of basic research and practical application faced currently by the composite SPEs were discussed and the solutions to these problems were given. It is hoped that this review can provide ideas for the design and preparation of future composite SPEs.
The functionalized graphene, with prominent capability over expansion of interlayer spacing and enhancement of sodium ion diffusivity, has gained paramount interests in fabricating anode of sodium ion batteries(SIBs). Here, a poly(sodium 4-vinylbenzenesulfonate)graphene composite(PSS-rGO) was synthesized via an in situ insertion process. The insertion structure is based on the π-π interaction between the electron of graphene and the electron of PSS, which expands the interlayer spacing of rGO and, more importantly, stabilizes the structure of the composites, restrains the stack of graphene. Beyond that, the introduced sodium sulfonate groups are capable of increasing the diffusion rate of sodium ions for fast sodium ion adsorption, ensuring superior cycling performance. The performances of the simples were characterized by scanning electron microscopy(SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD), Raman spectrometer(Raman), X-ray photoelectron spectrometer(XPS), electrochemical workstation and battery detection system. The results show the PSS-rGO remains a reversible capacity of 256 mAh·g-1 at 5 A·g-1 after 6000 cycles, with an ultralow decay rate of 0.003%. This work provides a feasible avenue for exploring advanced organic-inorganic hybrid materials with high capacity, fast sodium storage and ultralong lifespan for SIBs.
Two-dimensional layered MoS2 is considered to be a promising electrocatalyst alternative to Pt for water splitting. However, low electronic conductivity and high energy barrier of water adsorption/dissociation of MoS2 during alkaline hydrogen evolution reaction (HER) limit its application in water splitting. In this work, the smoothly anchored of MoS2 nanosheet on carbon cloth (CC) was prepared by one-pot hydrothermal method. The CC can significantly improve the electronic conductivity. Subsequently, the MoS2 nanosheet supported ultra-small Ru nanoparticles were controllably prepared by solvothermal reaction through immersing CC@MoS2 in an ethanol solution containing RuCl3 and finally formed CC@MoS2/Ru heterostructure. Ru can promote water adsorption/dissociation, and then synergistically catalyze HER with MoS2. The CC@MoS2/Ru is characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and transmission electron microscope (TEM), etc. The results show that the MoS2 nanosheets crossedly aligned on the CC, and the ultra-small Ru nanoparticles (average grain diameter of 2.5 nm) are dispersed homogeneously on the MoS2 nanosheets. The CC@MoS2/Ru is working electrode, the graphite rod and Hg/HgO are counter and reference electrodes, respectively. The alkaline HER are tested and the overpotential is only 71.3 mV to achieve the current density of -10 mA·cm-2, the Tafel slope of CC@MoS2/Ru is 104.8 mV·dec-1. The chronopotentiometry is performed at -10 mA·cm-2 to evaluate the stability of CC@MoS2/Ru. After the 35 h, the neglectable potential attenuation can be observed.
As a new energy material of environmental protection, biomass porous carbon material has been a research hotspot in recent years. In this paper, the porous carbon materials from lettuce leaves (LLs-temperature-proportional-activator) were prepared under different conditions, such as sintering temperature, the different activator, and the mass ratio of raw material and the activator, and the technological conditions were optimized through the discussion on their lithium storage performances. The results show that there are two broad and weak XRD peaks at 2θ=22°-26° and 2θ≈43° in each material, corresponding to the lattice plane (002) and (101), which indicates that the material is an amorphous carbon material with a certain degree of graphitization. In addition, the first discharge capacity of LLs-800-4R-K can reach 674.5 mAh/g. After 200 cycles, its discharge specific capacity can be maintained at 209.6 mAh /g, and the energy density is 146.8 Wh/kg. It illustrates that LLs-800-4R-K has good cycle performance and specific capacity. Thus, the optimum process conditions are as follows. The sintering temperature is at 800 ℃, KOH is used as activator, the mass ratio of raw material and the activator is 1:4.
Wire arc additive manufacturing (WAAM) attracts much attention due to its unique feature of rapid near net shape forming without die. It has the potential to become an advanced manufacturing technology that can break the bottleneck of alloy development and industrial application for aluminum materials. Wire arc additive manufacturing technology originates from traditional arc welding, and both of them use high-energy arc as heat source and metal wires as raw material. The WAAM technology and equipment development, the solidification and solid state phase transformation performance, microstructures, metallurgical defects as well as mechanical property of aluminum alloys were reviewed. The technique prospects of hot wire and multi-wire additive manufacturing, the unique fabrication manner and the exclusive phase transformation microstructure were discussed. The WAAM-specialized approaches to address the issues of poor manufacturing accuracy, serious porosity and cracking, and unsatisfied mechanical property, including fabrication system development, metallurgical defect controlling, alloy composition and microstructure design and heat treatment optimization were proposed. Such proposals are expected to facilitate the rapid development of high-end, customized and distinguished aluminum alloys via WAAM.
Graphene is widely considered a promising candidate for microwave absorbing materials in the future due to its unique dielectric properties, high specific surface area, low density and other outstanding properties. However, the single component graphene has poor microwave absorbing properties, so graphene-based microwave absorbing composites have become a research hotspot in recent years. In this paper, microwave absorbing mechanism and characteristics of graphene and its composites were introduced. Accordingly, it indicates that dielectric graphene microwave absorbing composites have the potential to become lightweight, high-intensity, broadband, and thin-layer microwave absorbing materials.The research progress in dielectric graphene microwave absorbing composites was reviewed from two aspects of graphene matrix and dopant.Finally, it was pointed out that developing new dielectric dopants with strong loss ability, constructing microwave absorbing composites with multiple components, establishing common design methods, as well as exploring large scale preparation methods would become the research trends in the future.
MXene is a two-dimensional (2D) layered material composed of early transition metal carbides, nitrides and carbonitride. Due to MXene's unique layered morphology, high electrical conductivity, high specific surface area, excellent hydrophilicity and good thermal stability, it has broad application prospect in the fields of physics, materials, chemistry and nanotechnology. It can also be used in a variety of scientific fields such as catalysis, energy storage and sensors. This paper mainly reviews the research progress in electrochemical sensors based on MXene. Firstly, the principle, composition, electrode surface modification of electrochemical sensors and the preparation methods of MXene were introduced. Then, the research progress of MXene in electrochemical enzyme sensors, electrochemical non-enzyme sensors, electrochemical immunosensors, electrochemical aptamer sensors and electrochemical molecularly imprinted sensors were reviewed. Finally, the industrialization and commercialization of MXene electrochemical sensing field, and the challenges of the development of new types of MXene were pointed out. The applications of MXene in various analytes and more potential fields were also prospected.
In order to better promote the research and development of high energy storage density and high efficiency lead-free ceramic dielectric capacitors, a comprehensive introduction to the energy storage principle and classification of ceramic dielectric energy storage materials was presented, the research progress, main research systems and performance advantages and disadvantages of linear dielectric, ferroelectric, relaxed ferroelectric and antiferroelectric energy storage materials in recent years were comparatively analyzed. The current challenges faced by ceramic energy storage materials and strategies to improve their energy storage were summarized. The current challenges of ceramic energy storage materials and the strategies to improve their energy storage performance were summarized, and their future development and applications were also presented.
Nitrogen doped porous carbon nanopolyhedra (NPC) derived from ZIF-8 was firstly prepared by high temperature carbonization. Subsequently, copper and cobalt were decorated on NPC to form novel nanocomposite by one-step chemical reduction method. Cu@Co/NPC hybrid material was characterized using X-ray powder diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The composite was modified on the surface of glassy carbon electrode to study its electrochemical response to hydrazine. The results show that Cu@Co /NPC nanocomposites play a synergistic role, which shows better electrocatalytic effect on hydrazine than single component modified electrode. Under the optimum conditions, the concentration of composite modified electrode and hydrazine in the range of 5-1850 μmol/L exhibits good linear relationship, and the detection limit is 0.08 μmol/L. In addition, the composite modified electrode has good stability, reproducibility and selectivity for the determination of hydrazine. It has been successfully used for the determination of hydrazine in environmental water samples with satisfactory results.
In order to solve the overheating failure problem of mechanical brakes of special tracked vehicles, SiC/Cu and SiC/Fe bi-continuous composites were prepared by squeeze casting method. The friction and wear properties of the two composites under continuous emergency braking and continuous high temperature braking conditions were studied. The variation of friction coefficient, temperature and wear rate was analysed by means of scanning electron microscopy (SEM), X-ray energy dispersive spectrometry (EDS) and 3D profiler, and the wear mechanism was described. The results show that in the continuous emergency braking test, the contact surface experiences the process of tribo-film formation and interlayer fracture.Friction coefficient decreases slightly with the increase of joining times and tends to be stable. In the first 40 joining, the wear rates of SiC/Cu and SiC/Fe friction pairs decrease overall. During 40-60 joining, the adhesion wear, oxidation wear and fatigue wear of the SiC/Cu friction pair are aggravated, and the wear rate increases, while the wear rate of the SiC/Fe friction pair is mainly abrasive wear, and the wear rate is low. In the continuous high temperature braking test, the friction coefficient increases gradually and the braking time decreases gradually in the first six joining. After the sixth joining, the adhesion wear and fatigue wear in the edge area of the friction pair result in the decrease of the torque, and the friction coefficient and braking time both show a trend of decrease at first and then increase. In the process of continuous high temperature braking, severe adhesive wear is the main factor. The wear rates of SiC/Cu and SiC/Fe friction pairs increase with the increase of joining times.
The direct pyrolysis method was adopted with graphene as the carrier, 2-methylimidazole zinc salt MAF-4(ZIF8) and urea to provide carbon and nitrogen sources, Fe as the transition metal source, to synthesize nitrogen-doped graphene(N/GO) and Fe-ZIF8(N-GO@Fe/ZIF8) composite catalyst, assembled into a zinc-air battery. The physical-chemical properties of the catalyst were characterized by using scanning electron microscope(SEM), transmission electron microscope(TEM) and rotating disk electrode. The results show that the synthesized N-GO@Fe/ZIF8-900 catalyst has excellent oxygen reduction/oxygen evolution (ORR/OER) performance. The half wave potential is 0.885 V, which is better than that of Pt/C (0.856 V). When oxygen is precipitated, the corresponding potential is 1.811 V at a current density of 10 mA/cm2, which is better than that of the noble metal Pt/C (1.968 V) and the same performance as IrO2 (1.75 V).After being assembled into a zinc air battery, the specific energy and power density reach 886.2 mW·h·g-1 and 73.44 mW/cm2 respectively, which are higher than that of Pt/C (791.04 mW·h·g-1, 57.12 mW/cm2) respectively. The catalyst has good application prospect.
Modification and doping of carbon support are the main ways to improve the performance of the platinum-based catalyst for proton exchange membrane fuel cell. FeN-BP.Iron and nitrogen(FeN) co-doped activated carbon (Black Pearl 2000, BP) as a support, was used as the support of platinum-based catalyst for oxygen reduction reaction (ORR). The activity and stability of the catalysts were tested by electrochemical techniques, and the structure of the catalysts were characterized by X-ray diffraction, specific surface area and pore size distribution test, transmission electron microscopy, X-ray photoelectron spectroscopy. The results show that Pt/FeN-BP and commercial Pt/C catalyst have comparable initial ORR activity with onset potential 0.94 V. After accelerated degradation test, the lost of onset potential for Pt/FeN-BP catalyst and commercial Pt/C catalyst are about 10 mV and 30 mV, as well as the lost of half-wave potential are about 5 mV and 60 mV.Pt/FeN-BP catalyst shows obvious improved stability.The high surface area and the moderate pore size distribution of FeN-BP, the small size and well dispersion of Pt nanoparticles on carbon after accelerated degradation test, as well as the interaction between carbon support and Pt nanoparticles may the key reasons for Pt/FeN-BP with improved stability.
The TiC-reinforced Ti-based coating was prepared in-situ on the surface of the titanium alloy TA15 by laser cladding technology. The forming quality, microstructure, phase composition, hardness, and tribological properties were investigated by optical microscope, X-ray diffractometer, scanning electron microscope, energy spectrum analyzer, microhardness tester and friction and wear apparatus. The results show that the coating mainly composes of β-Ti, Co3Ti, CrTi4 and TiC, and the good metallurgical bond is formed between coating and the substrate. The microstructure of the coating bond zone is planar crystal and columnar crystal, the middle is dendritic, and the top is equiaxed. Significant differences in the morphology of TiC are observed in each micro-area of the coating. TiC of the top and middle areas is thick dendritic and petal-like, while TiC of the bonding area is needle-like and spherical. The maximum microhardness of the coating is 715HV, which is about 2.1 times than that of TA15 (330HV). Under the same conditions, the wear loss of coating is 30.14 mg, which is about 30.7% of TA15(98.11 mg). The wear mechanism of the cladding coating and substrate is a composite wear mode of adhesive wear and abrasive wear, but the wear degree of the coating is lighter.
The microstructure evolution, tensile properties and fracture behavior of five-element Ti2AlNb alloy Ti-22Al-23Nb-1Mo-1Zr (atom fraction/%) ring forging at different solution temperatures of 850, 880, 900 ℃ and 750 ℃ aging treatment (AT) were studied by scanning electron microscope (SEM), transmission electron microscopy (TEM) and mechanical testing machines. The results show that with the increase of solution temperature, the fine lamellar O phase is more solid-dissolved into the B2 phase matrix, the coarse lamellar O phase gradually becomes coarser and the volume fraction of O phase decreases after solution treatment (ST). After ST+AT, a very small amount of fine lamellar O phase precipitates from the B2 phase matrix at a higher solution temperature, coarse lamellar O phase is coarsened, the volume fraction of O phase tends to be the same. The tensile strength of the alloy decreases, while the ductility increases with the increase of solution temperature. The tensile fracture morphology is a quasi cleavage characteristic of typical cleavage and dimple mixed fracture. There are microcracks, slip characteristics and the bending O phase elongated along tensile direction in the longitudinal fracture. Dislocations distribute along the B2/O phase boundary. The small size of the lamellar O phase can effectively reduce the dislocation slip distance, resulting in strong strengthening effect.
Different thermal-oxidative environments (70, 130 ℃ and 190 ℃) have important effects on the properties of carbon fiber composites. The mass loss characteristics of T800 carbon fiber/epoxy resin composites under different thermal-oxidative environments were analyzed, and the surface morphology, infrared spectra, dynamic mechanical properties and interlaminar shear properties of T800 carbon fiber/epoxy resin composites before and after aging were compared. The results show that in the initial stage of thermal-oxidative aging, the mass loss rate is increased rapidly, and the higher the aging temperature, the faster the mass loss. The extent of damage sample surface morphology is gradually increased with the increasing of thermal-oxidative temperature, after aging at 190 ℃, the resin on the fiber surface falls off seriously, the cracks and gaps appear between the fibers, and there is no resin filling, at this aging temperature, the sample has an irreversible chemical change. The glass transition temperature of the sample is increased with the increase of aging temperature, but the internal friction is decreased at first, then increased and then decreased. After thermal-oxidative aging at 70, 130 ℃ and 190 ℃, the shear strength of the samples is increased by 6.0%, 13.7% and 2.1%, respectively. The relevant test results and phenomena can provide data reference for the follow-up study of the new domestic T800 carbon fiber/epoxy composites.
The microstructure evolution and mechanical behavior of an Fe-33Mn-4Si alloy steel under low-cycle fatigue deformation were investigated by using the X-ray diffraction and electron backscatter diffraction techniques.Results show that the experimental steel has an initial microstructure consisting of austenite and thermally induced ε-martensite. The initial microstructure remarkably affects the low-cycle fatigue property of the experimental steel through influencing the ε-martensitic transformation during deformation. At the early stage of fatigue deformation (first 100 deformation cycles), with increasing deformation cycles, a rapid increase in the volume fraction of ε-martensite and the frequency of the intersection of ε-martensite with different variants result in a quick rise in cyclic average peak stress and work hardening degree. With the continuation of cyclic deformation up to fatigue fracture, the ε-martensite becomes the dominant constituent phase in the deformation microstructure, and the volume fraction of ε-martensite and the frequency of the intersection of ε-martensite increase at an appreciably slower rate, thereafter significantly slowing the increase in cyclic average peak stress and work hardening degree.
The rolling-heat treatment process can significantly improve the strength of D6A steel. In order to explore the toughening mechanisms of D6A alloy steel, the micrometer grade D6A alloy steel is obtained by hot rolling and intercritical warm rolling plus annealing process, which consists of ferrite matrix and granular cementite. The microstructure and mechanical properties of the experimental steel were characterized by tensile test at room temperature, SEM, X-ray diffraction and EBSD. The results show that the grain size is refined from 4.5 μm to 1.5 μm with the increase of rolling pass, the cementite content increases gradually, and the proportion of grain boundary with small angle increases. The yield strength and tensile strength increase continuously, while the elongation decreases slightly, indicating that the size of subgrain decreases continuously during the rolling process, grain boundary area, and the resistance to dislocation slip increase. At the same time, the dislocation density of the experimental steel with different rolling pass was calculated. When the thickness reduction is 88%, the dislocation density is the highest, and then the degree of working hardening is the highest. The analysis shows that with the increase of the deformation, the strength increment caused by the strengthening of the second phase and grain refinement shows an increasing trend, while the strength increment caused by dislocation enhancement first increases and then decreases. The main strengthening methods of D6A steel are second phase strengthening, fine grain strengthening and dislocation strengthening.