High In-plane Electrical Conductivity Research Articles

Anchoring Pt nanoparticle onto monolayer VS2 nanosheets boost efficient acidic hydrogen evolution

The electrocatalytic hydrogen evolution reaction (HER) is a key technology for hydrogen production and plays a significant role in advancing sustainable energy conversion. This study successfully anchored platinum (Pt) nanoparticles onto monolayer VS2 nanosheets via a colloidal chemistry method to enhance their HER performance under acidic conditions. The monolayer VS2 nanosheets provide a stable substrate, with their large surface area and high in-plane electrical conductivity effectively enhancing the interfacial electron transfer and electrochemical contact of the Pt nanoparticles. The Pt/VS2 composite material significantly reduces the energy barrier required for HER and enhances electrochemical activity, while also lowering the cost of the catalyst. At a current density of 10 mA cm−2, the composite material with Pt nanoparticles anchored onto VS2 nanosheets achieved an overpotential of just 26 mV and exhibited a high mass activity of 23.7 A/mgPt. Density functional theory (DFT) calculations and experimental analyses further elucidated the critical role of interfacial electronic effects and sulfur vacancy modulation in enhancing catalytic efficiency. These findings highlight the potential of interface engineering to control electronic structure and sulfur vacancies, significantly enhancing the hydrogen production efficiency and cost-effectiveness of Pt-based catalysts even at low Pt loadings under acidic conditions.

Nanofiber derived MXene composite paper for electromagnetic shielding and thermal management

Despite the urgent demands in protecting wearable electronics from electromagnetic interference (EMI) in various conditions, it remains challenging to attain mechanically robust and flexible materials with both excellent EMI shielding and thermal managing performance. Herein, we report MXene composite paper that can provide multifunction with superior mechanical properties. To construct a hierarchical composite with 2D/0D reinforcements, the MXene paper is fabricated by hot pressing of electrospun Poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibers incorporated with MXene nanosheets and carbon black nanoparticles. Due to the laminated structure connected by nanoparticles, the flexible composite paper shows remarkable mechanical strength and fatigue resistance that can provide stable EMI shielding effectiveness of 500 dB/mm even after 10000th cyclic rolling. Moreover, the high in-plane electrical conductivity and out-of-plane thermal conductivity allow a fast electrothermal heating and cooling behavior, which qualifies the MXene paper as multifunctional surface for wearable electronics.

Effect of Anisotropy of Reduced Graphene Oxide on Thermal and Electrical Properties in Silicon Carbide Matrix Composites.

Reduced graphene oxide, due to its structure, exhibits anisotropic properties, which are particularly evident in electrical and thermal conductivity. This study focuses on examining the influence of reduced graphene oxide in silicon carbide on these properties in directions perpendicular and parallel to the direction of the aligned rGO flakes in produced composites. Reduced graphene oxide is characterized by very high in-plane thermal and electrical conductivity. It was observed that the addition of rGO increases thermal conductivity from 64 W/mK (reference sample) up to 98 W/mK for a SiC-3 wt.% rGO composite in the direction parallel to the rGO flakes. In the perpendicular direction, the values were slightly lower, reaching up to 84 W/mK. The difference observed in electrical conductivity values is more significant and is 1-2 orders of magnitude higher for the flakes' alignment direction. The measured electrical conductivity increased from 1.2710-8 S/m for the reference SiC sinter up to 1.55 × 10-5 S/m and 1.2410-4 S/m for the composites with 3 wt.% rGO for the perpendicular and parallel directions, respectively. This represents an enhancement of four orders of magnitude, with a clearly visible influence of the anisotropy of the rGO. The composite's enhanced electrical and thermal conductivity make it particularly attractive for electronic devices and high-power applications.

Temperature-modulated synthesis of vertically oriented atomic bilayer graphene nanowalls grown on stainless steel by inductively coupled plasma chemical vapour deposition

It is now clear that growing flat graphene nanostructures from the gas phase on planar substrates is possible. One of the keys to success —particularly in producing a very large specific surface in a reduced space— is the use of 3D carbon nanostructures (i.e., vertical graphene nanowalls, VGNWs) over a planar substrate as a growth template for the deposition of electrochemically active materials (as, for example, transition metal oxides (TMO)). Vertical graphene nanowalls, also known as petal-like, vertical graphene flakes or vertical graphene, can achieve a very large specific surface area of 1100 m2/g, which is comparable to or greater than that of carbon nanotubes —the reference material for its use in high-performance supercapacitors or in other energy-related applications requiring a large active surface area. Vertical graphene nanowalls also exhibit high vertical and in-plane electrical conductivity when grown on metal electrodes, which benefits their use in electrochemical applications. Here, we focus on the growth of VGNWs on flexible stainless-steel substrates (SS310), in principle suitable for applications to electrodes of electrochemical systems (batteries, supercapacitors, catalysts), by inductively coupled plasma chemical vapour deposition (ICP-CVD), from methane as a carbon precursor, in a wide range of temperatures (575 to 900 °C). We will discuss the effect of growth temperature on morphological and structural characteristics of VGNWs based on the results of Raman spectroscopy and field emission scanning electron microscopy (FE-SEM) analysis. Because the nanostructures of graphene nanowalls reported to date are, for the most part, based on multi-layered graphene, here we seek to highlight the effect of temperature on the number of atomic layers of VGNW. In the 700–750 °C range, and under the plasma conditions explored, vertical graphene nanowalls are bilayer, which is foreseen to directly affect the magnitude of the VGNW specific surface.

Tuning of anisotropic electrical conductivity and enhancement of EMI shielding of polymer composite foam via CO2-assisted delamination and orientation of MXene

Integration of a foam structure into a shielding material not only reduces its mass density but also enhances its electromagnetic interference (EMI) shielding performance. In this study, poly(vinylidene fluoride) (PVDF) composite films and foams consisting of carbon nanotubes (CNTs) and bulk Ti3C2Tx MXenes were fabricated. Prominent anisotropy with high in-plane electrical conductivity (σ∥) and low through-plane electrical conductivity (σ⊥) was achieved (e.g., σ∥ = 17.02 S/m and σ⊥ = 0.42 S/m with 1 wt% MXenes) in the composite films due to the aligned structure of the MXenes in the PVDF matrix. With CO2-assisted foaming, the intercalation of PVDF chains and cell-induced biaxial stretch facilitated reorganized orientation and delamination of the MXenes. Consequently, σ∥ decreased and σ⊥ increased, and exhibiting an isotropic feature. Furthermore, the integration of the foam structure resulted in an increased σ⊥, which improved the EMI shielding effectiveness (EMI SE) to 65.1 dB at a MXene content of 12 wt%, owing to enhanced multi-reflections, dielectric loss and conduction loss. Moreover, the shielding effectiveness coming from reflection was reduced to lower than 3 dB due to the decrease in σ∥ and destructive interference in the composite foam, thus leading to an absorption-dominated mechanism. Additionally, the prepared composite foams exhibited outstanding thermal conductivity and mechanical strength, enabling them to be used as lightweight and robust EMI shielding materials that could transform EM wave energy into Joule heat.

Layered structure of alumina/graphene-augmented-inorganic-nanofibers with directional electrical conductivity

Implementation of layered structures with strong nanoscale optimized interfaces, enables engineering of materials with functional properties. In this work, anisotropic functional multi-layered structures are produced by integration of a thin hybrid inter-layer of graphene-augmented-nanofibers/alumina into α-alumina through an ex-situ strategy of precipitating the tailored hybrid from a solution. Spark plasma sintering was used to consolidate the layered structures at 1150 and 1450 °C under 75 and 50 MPa pressure. Raman spectroscopy suggests presence of C–H bonds and sp3 hybridization for the samples sintered at 1150 °C, while graphene structure is purified at the sintering temperature of 1450 °C. The multilayer structures demonstrate a high in-plane electrical conductivity which can be modulated, ranging from 300 to 1800 S m−1 as a function of the interlayer thickness and the carbon content. A p-type conduction at room temperature and n-type down to 4 K in graphene-augmented nano-fillers was observed in Hall measurement. However, the multilayered systems display a p-type conduction in the entire temperature range. Hardness was preserved despite the high concentration of the graphene-augmented nano-fillers in the hybrid interlayer leaving a highest value of ∼22 GPa. The results have the potential to fuel the development of functional electronic enclosures with additional functionalities such as electromagnetic interference shielding.

Quasi one-dimensional van der Waals gold selenide with strong interchain interaction and giant magnetoresistance

The atomic structure of quasi one-dimensional (1D) van der Waals materials can be regarded as the stacking of atomic chains to form thin flakes or nanoribbons, which substantially differentiates them from typical two-dimensional (2D) layered materials and 1D nanotube/nanowire array. Here we present our studies on quasi 1D gold selenide (AuSe) that possesses highly anisotropic crystal structure, excellent electrical conductivity, giant magnetoresistance, and unusual reentrant metallic behavior. The low in-plane symmetry of AuSe gives rise to its high anisotropy of vibrational behavior. In contrast, quasi 1D AuSe exhibits high in-plane electrical conductivity along the directions of both atomic chains and perpendicular one, which can be understood as a result of strong interchain interaction. We found that AuSe exhibits a near quadratic nonsaturating giant magnetoresistance of 1841% with the magnetic field perpendicular to its in-plane. We also observe unusual reentrant metallic behavior, which is caused by the carrier mismatch in the multiband transport. Our works help to establish fundamental understandings on quasi 1D van der Waals semimetallic AuSe and identify it as a new candidate for exploring giant magnetoresistance and compensated semimetals.

Highly-conductive composite bipolar plate based on ternary carbon materials and its performance in redox flow batteries

Redox flow battery has become one of the most promising technologies for large-scale energy storage. However, as a key component, bipolar plate is still under development to achieve high electrical conductivity and sufficient flexural strength simultaneously. With this purpose, an innovative low-carbon-content bipolar plate with hybrid conductive materials of graphene, carbon fibers and graphite powders are prepared. Morphology, flexural strength, electrical conductivity, corrosion resistance, vanadium permeability and single cell performance are studied and discussed. Extremely low area specific resistance (5.0 mΩ cm2) and high in-plane electrical conductivity (420.6 S cm−1) are achieved at an ultra-low carbon content of 25 wt%. The voltage efficiency and energy efficiency of the vanadium redox flow battery unit cell reach as high as 88.0% and 85.9%, respectively, at 100 mA cm−2. The low-carbon-content bipolar plate turns to be promising for the massive application in redox flow batteries.

Electrically Conductive and Mechanically Strong Graphene/Mullite Ceramic Composites for High-Performance Electromagnetic Interference Shielding.

Ceramic composites with good electrical conductivity and high strength that can provide electromagnetic interference (EMI) shielding are highly desirable for the applications in harsh environment. In this study, lightweight, highly conductive, and strong mullite composites incorporated with reduced graphene oxide (rGO) are successfully fabricated by spark plasma sintering at merely 1200 °C using the core-shell structured γ-Al2O3@SiO2 powder as a precursor. The transient viscous sintering induced by the γ-Al2O3@SiO2 precursor not only prohibits the reaction between mullite and rGO by greatly reducing the sintering temperature, but also induces a highly anisotropic structure in the rGO/mullite composite, leading to an extremely high in-plane electrical conductivity (696 S m-1 for only 0.89 vol % of rGO) and magnitude lower cross-plane electrical conductivity in the composites. As a result, very large loss tangent and EMI shielding effectiveness (>32 dB) can be achieved in the whole K band with extremely low rGO loading (less than 1 vol %), which is beneficial to maintain a good mechanical performance in ceramic matrix composites. Accordingly, the rGO/mullite composites show greatly improved strength and toughness when the rGO content is not high, which enables them to be applied as highly efficient EMI shielding materials while providing excellent mechanical performance.

A new approach to prepare fully dense Cu with high conductivities and anti-corrosion performance by cold spray

A novel approach has been developed to cold spray fully dense Cu deposits by using a mixed feedstock. The feedstock is composed of two raw powders with remarkably dissimilar microstructure and hardness: a hard and dense gas-atomized Cu powder (GA Cu) and a soft and porous electrolytic Cu powder (E Cu). It was found that when high velocity impact occurs between dissimilar Cu particles, the plastic deformation shows an asymmetrical feature and the strain is mainly concentrated on the soft side. This asymmetrical deformation behavior ensures that all the inter-particle space can be filled by the deformed soft particles and leads to a fully dense microstructure. An increment of ∼44% in deposition efficiency was achieved for the mixed feedstock as compared with the GA Cu powder. A high in-plane electrical conductivity of 79 %IACS (73 and 56 %IACS for GA coating and E coating, respectively) and high through thickness thermal conductivity of 285.6 W m−1 K−1 (207.1 and 133.8 W m−1 K−1 for GA coating and E coating, respectively) were achieved. The coating prepared by mixed powders shows an excellent corrosion resistance, comparable with that of the bulk Cu. This work gives a new strategy to improve the inter-particle bonding and get fully dense metallic deposits by feedstock design rather than spraying condition optimization.

Multifunctional non-woven fabrics of interfused graphene fibres.

Carbon-based fibres hold promise for preparing multifunctional fabrics with electrical conductivity, thermal conductivity, permeability, flexibility and lightweight. However, these fabrics are of limited performance mainly because of the weak interaction between fibres. Here we report non-woven graphene fibre fabrics composed of randomly oriented and interfused graphene fibres with strong interfibre bonding. The all-graphene fabrics obtained through a wet-fusing assembly approach are porous and lightweight, showing high in-plane electrical conductivity up to ∼2.8 × 104 S m−1 and prominent thermal conductivity of ∼301.5 W m−1 K−1. Given the low density (0.22 g cm−3), their specific electrical and thermal conductivities set new records for carbon-based papers/fabrics and even surpass those of individual graphene fibres. The as-prepared fabrics are further used as ultrafast responding electrothermal heaters and durable oil-adsorbing felts, demonstrating their great potential as high-performance and multifunctional fabrics in real-world applications.

Advanced Silicon-Graphene Anodes for High Performance Applications

Rechargeable batteries with improved energy and power density have many potential, high impact applications including advanced portable electronics and electric vehicles. However, most ‘next-generation’ materials capable of providing improved performance suffer from rapid capacity degradation or severe loss of capacity when rapidly discharged. Silicon is a promising anode material that is widely investigated as a potential successor for graphite since it can store significantly more energy per mass and volume. Tremendous advancement towards commercialization of silicon anodes – including improving cycle life and minimizing electrode swelling – has been made over the past decade. Proper electrode engineering has brought silicon-based anode materials closer to commercialization into consumer applications. However, cycle life and irreversible capacity losses (ICL) due to side reactions continue to be issues that plague their widespread use. However, silicon technology has not yet been significantly commercialized due to a number of shortcomings. Graphene, an atomically thin version of graphite widely regarded as a wonder material, has the potential to overcome many of the remaining issues due to graphene’s unique combination of high surface area, high in-plane electrical conductivity, excellent tensile modulus and mechanical durability. In this presentation, we will describe the approaches and architectures employed using silicon-graphene composites to accelerate their development as well as remain challenges to be solved. SiNode Systems is a battery materials venture developing silicon-graphene anodes for the next generation of lithium-ion batteries. SiNode anodes offer higher battery capacity and faster charging rates, all while being produced via a low cost solution chemistry-based manufacturing process. SiNode seeks to change the landscape for lithium-ion batteries so they can meet the demands of a wide range of industries, from consumer electronics to electric vehicles.

Hierarchical composites with high-volume fractions of carbon nanotubes: Influence of plasma surface treatment and thermoplastic nanophase-modified epoxy

A scaled-up catalytic chemical vapor deposition synthesis approach has been used to grow carbon nanotubes (CNTs) onto quartz and alumina fibers to prepare novel hierarchically structured composites with high volume fractions of CNTs. The as-synthesized CNT-coated fibers were functionalized using atmospheric oxygen plasma, prior to infusing an epoxy polymer matrix, in order to improve wettability and bonding. The polymer matrix was further modified by adding a triblock copolymer to provide nanoscale toughening. Direct adhesion tests show that CNT and plasma treatments increase the shear strength of quartz or alumina/epoxy films by 30%. CNT–quartz/epoxy composites show an 80% increase in the in-plane shear strength while the CNT–alumina/epoxy composites show more than a threefold increase in shear strength. The failure mechanisms of the films and the fiber composites are dominated by fracture through the catalytic iron nanoparticles and the improvements are limited by the CNT to fiber adhesion. The composites also have very high in-plane electrical conductivity, over 3S/cm. The carbon nanotubes form a piezoresistive sensing network surrounding the fibers. Under flexural loading the change in electrical resistance can detect damage initiation and impending fracture, particularly for the alumina composites.

Platinum-induced structural collapse in layered oxide polycrystalline films

Effect of a platinum bottom electrode on the SrBi5Fe1−xCoxTi4O18 layered oxide polycrystalline films was systematically studied. The doped cobalt ions react with the platinum to form a secondary phase of PtCoO2, which has a typical Delafossite structure with a weak antiferromagnetism and an exceptionally high in-plane electrical conductivity. Formation of PtCoO2 at the interface partially consumes the cobalt dopant and leads to the structural collapsing from 5 to 4 layers, which was confirmed by X-ray diffraction and high resolution transmission electron microscopy measurements. Considering the weak magnetic contribution from PtCoO2, the observed ferromagnetism should be intrinsic of the Aurivillius compounds. Ferroelectric properties were also indicated by the piezoresponse force microscopy. In this work, the platinum induced secondary phase at the interface was observed, which has a strong impact on Aurivillius structural configuration and thus the ferromagnetic and ferroelectric properties.

Fabrication of LSM-SDC composite cathodes for intermediate-temperature solid oxide fuel cells

Microstructure, interfacial resistance, and activation energy for composite cathodes consisting of 50 wt% (La0.85Sr0.15)0.9MnO3-δ (LSM) and 50 wt% Sm0.2Ce0.8O1.90 (SDC) were studied for intermediate-temperature solid oxide fuel cells based on SDC electrolytes. Microstructure and interfacial resistance were greatly influenced by the characteristics of starting powder and temperatures sintering the electrodes. Optimum sintering temperatures were 1100 and 950 °C, respectively, for electrodes with SDC prepared using oxalate coprecipitation technique (OCP) and glycine-nitrate process (GNP). Area-specific resistances determined using impedance spectroscopy were 0.47 and 0.92 Ω cm2 at 800 °C for LSM-SDC/OCP and LSM-SDC/GNP, respectively. The high electrochemical performance is attributed to small grain size, high porosity, and high in-plane electrical conductivity of composite cathode, demonstrating the dramatic effects of microstructure on electrode performance. To increase the electrode performance, it is critical to enhance the diffusion rate of oxygen species.

Effect of small-sized conductive filler on the properties of an epoxy composite for a bipolar plate in a PEMFC

Abstract This paper focused on using a conductive polymer composite (CPC) as a potential replacement for the conventional graphite bipolar plate used in polymer electrolyte membrane fuel cells (PEMFC). Based on the requirements established by the US Department of Energy (DOE), the in-plane electrical conductivity and flexural strength are required to be greater than 100 S/cm and 25 MPa, respectively. The high filler loading is needed to satisfy the high in-plane electrical conductivity. However, the high filler loading reduces the flexural strength and manufacturability of the composite. In this study, the composites were prepared by compounding using an internal mixer followed by compression moulding. The combination of 10 vol% carbon black (CB) as the second filler with synthetic graphite/epoxy (SG/EP) resulted in the following composite properties: 150 S/cm (in-plane conductivity), 55 S/cm (through-plane conductivity), and 38.8 MPa (flexural strength). Used as the second filler, the CB, which had a small-sized diameter, formed conductive networks that filled the voids between the SG and polymer matrix. The in-plane electrical conductivity and flexural strength of the CB/SG/EP composites at the optimum composition exceeded the requirement for bipolar plate applications.

Highly Conductive and Porous Activated Reduced Graphene Oxide Films for High-Power Supercapacitors

We present a novel method to prepare highly conductive, free-standing, and flexible porous carbon thin films by chemical activation of reduced graphene oxide paper. These flexible carbon thin films possess a very high specific surface area of 2400 m(2) g(-1) with a high in-plane electrical conductivity of 5880 S m(-1). This is the highest specific surface area for a free-standing carbon film reported to date. A two-electrode supercapacitor using these carbon films as electrodes demonstrated an excellent high-frequency response, an extremely low equivalent series resistance on the order of 0.1 ohm, and a high-power delivery of about 500 kW kg(-1). While higher frequency and power values for graphene materials have been reported, these are the highest values achieved while simultaneously maintaining excellent specific capacitances and energy densities of 120 F g(-1) and 26 W h kg(-1), respectively. In addition, these free-standing thin films provide a route to simplify the electrode-manufacturing process by eliminating conducting additives and binders. The synthetic process is also compatible with existing industrial level KOH activation processes and roll-to-roll thin-film fabrication technologies.

Ultra-thin nanocrystalline lanthanum strontium cobalt ferrite (La 0.6Sr 0.4Co 0.8Fe 0.2O 3− δ) films synthesis by RF-sputtering and temperature-dependent conductivity studies

Nanocrystalline lanthanum strontium cobalt ferrite (LSCF) ultra-thin films with high in-plane electrical conductivity have been deposited by RF sputtering from composite targets. The films, with nominal thickness of 54 nm, are crystalline when annealed or deposited at temperatures above 450 °C. Effects of annealing temperature, annealing time, and substrate temperature on crystallization, microstructure, and room temperature lateral electrical conductivity have been systematically studied. No interfacial reaction products between the LSCF and single crystalline yttria-stabilized zirconia (YSZ) were observed from X-ray diffraction studies upon annealing until 750 °C. In-plane electrical conductivity as high as 580 S cm −1 at 650 °C has been observed for LSCF thin films deposited on single crystalline YSZ substrates and sputtered nanocrystalline YSZ thin films; while activation energy for conductivity were determined to be 0.15 eV and 0.10 eV for the former and latter films, respectively, in 650–400 °C range. The high in-plane electrical conductivity for the nanocrystalline LSCF ultra-thin films is likely attributed to their low level of porosity. Micro-solid oxide fuels cells using 15 nm thick LSCF films as cathodes and sub-100 nm yttria-doped zirconia thin film electrolytes have been fabricated successfully and demonstrated to achieve peak power density of 60 mW cm −2 at 500 °C. Our results demonstrate that RF sputtering provides a low-temperature synthesis route for realizing ultra-thin nanocrystalline LSCF films as cathodes for intermediate- or low-temperature solid oxide fuel cells.

An X-ray photoelectron investigation of conducting N-octadecylpyridinium-tetracyanoquinodimethane Langmuir-Blodgett films

A study of Langmuir-Blodgett films of the 1:1 charge transfer salt N-octadecylpyridinium-tetracyanoquinodimethane using X-ray photoelectron spectroscopy is reported. Examination of the nitrogen spectrum reveals three distinct environments for this atom, which are interpreted as corresponding to negatively-charged, neutral and positively-charged species. It is suggested that the presence of the neutral nitrogen accounts for the (relatively) high in-plane electrical conductivity that is observed for the as-deposited films.

Low temperature growth of pyrolytic carbon with well-ordered graphite structure by chemical vapour deposition methods

Carbon films with well-ordered graphite structure were successfully deposited on a quartz substrate by thermal decomposition of benzene gas at 1000°C. The improvement in the degree of preferred orientation to the substrate surface was verified by reflection high energy electron diffraction observations. Such good crystallinity of the films was shown to be responsible for high in-plane electrical conductivity ( σ | = 2.2 × 10 3 Ω -1 cm -1 ). Investigations concerning the film properties and their dependence on the deposition conditions will be described.