Ultrahigh Electrical Conductivity Research Articles

Carbon and carbon composites for thermoelectric applications

AbstractThe urgent need for consistent, reliable, ecofriendly, and stable power sources drives the development of new green energy materials. Thermoelectric (TE) materials receive increasing attention due to their unique capability of realizing the direct energy conversion between heat and electricity, showing diverse applications in harvesting waste heat and low‐grade heat. Carbon materials such as carbon nanotubes (CNTs) and graphene have experienced a rapid development as TE materials because of their intrinsic ultrahigh electrical conductivity and light weight. Besides, polymer‐based carbon composites are particularly fascinating as the combination of the merits of polymers and filler materials leads to high TE performance and superior flexibility. Herein, the recent TE advances are systematically summarized in the studied popularity of carbon materials (ie, CNTs and graphene) and the category of polymers. The conducting polymer‐based carbon materials are particularly highlighted. Finally, the remaining challenges and some tentative suggestions possibly guiding future developments are proposed, which may pave a way for a bright future of carbon and carbon composites in the energy market.

Ultrahigh electrical conductivities and low lattice thermal conductivities of La, Dy, and Nb Co-doped SrTiO3 thermoelectric materials with complex structures

Microstructural modifications and appropriate element doping are necessary to simultaneously enhance the electrical conductivities and reduce the lattice thermal conductivities of thermoelectric materials. Herein, we propose a strategy of multielement doping combined with a burial sintering process to promote thermoelectric properties. Three-element doped Sr0.9La0.05Dy0.05Ti1−xNbxO3 (x = 0, 0.05, 0.10, 0.15, and 0.20) powders were synthesized by high-energy ball milling, and corresponding bulk samples were prepared by carbon burial sintering. In the bulk samples, we obtained the desired microstructures composed of shell-vesicular architectures with dense dislocations and second phase particles. These materials had ultrahigh electrical conductivities (∼5300 S cm−1 at 300 K), low lattice thermal conductivities (∼1.6 W m−1 K−1 from 700 to 1100 K when x = 0.2) and low total thermal conductivities (minimum value of 2.95 W m−1 K−1 when x = 0.05 at 1100 K). The maximum zT values were 0.28 when x = 0.05 and 0.27 when x = 0.2 at 1100 K. This strategy provides a possible direction for improving the thermoelectric properties of SrTiO3 based materials.

Multifunctional Flexible Electromagnetic Interference Shielding Silver Nanowires/Cellulose Films with Excellent Thermal Management and Joule Heating Performances.

Flexible electromagnetic interference (EMI) shielding materials with excellent thermal conductivities and Joule heating performances are of urgent demand in the communication industry, artificial intelligence, and wearable electronics. In this work, highly conductive silver nanowires (AgNWs) were prepared using the polyol method. Cellulose sheets were then prepared by dissolving natural cotton in a green and efficient NaOH/urea aqueous solution. Finally, multifunctional flexible EMI shielding AgNWs/cellulose films were fabricated based on vacuum-assisted filtration and hot-pressing. AgNWs are evenly embedded in the inner cellulose matrix and overlap with each other to form a 3D network. AgNWs/cellulose films, with a thickness of 44.5 μm, obtain the superior EMI shielding effectiveness of 101 dB, which is the highest value ever reported for shielding materials with the same thickness. In addition, AgNWs/cellulose films present excellent tensile strength (60.7 MPa) and tensile modulus (3.35 GPa), ultrahigh electrical conductivity (σ, 5571 S/cm), and excellent in-plane thermal conductivity coefficient (λ∥, 10.55 W/mK), which can effectively dissipate the heat accumulation. Interestingly, AgNWs/cellulose films also show outstanding Joule heating performances, good stability, and sensitive temperature response at driving voltages, absolutely safe for the human body. Therefore, our fabricated multifunctional flexible AgNWs/cellulose films have broad prospects in the fields of EMI shielding and protection of outdoor large-scale power transformers and wearable electronics.

An Overview of Stretchable Supercapacitors Based on Carbon Nanotube and Graphene

The wearable demand of modern electronic devices makes flexible and stretchable energy storage device urgently needed. Stretchable and flexible supercapacitors (SCs) are energy storage devices that provide ultrahigh power density while having long-term durability, high security, and electrochemical stability. Among different SCs electrode materials, CNTs and graphene-based materials exhibit great potential in terms of stretchable SCs due to its ultrahigh electrical conductivity, large specific surface area and good mechanical properties. In this review, the state-of-the-art process and achievements in the field of stretchable SCs enabled by CNTs and graphene are presented, which include the novel design strategy, mechanical and electrochemical properties. The final section highlights current challenges and future perspectives on research in this thriving field.

A free-standing manganese cobalt sulfide@cobalt nickel layered double hydroxide core-shell heterostructure for an asymmetric supercapacitor.

Rational design of self-supported electrode materials is important to develop high-performance supercapacitors. Herein, a free-standing MnCo2S4@CoNi LDH (MCS@CN LDH) core-shell heterostructure is successfully prepared on Ni foam using the hydrothermal reaction and electrodeposition. In this architecture, the inner MnCo2S4 nanotube provides an ultra-high electrical conductivity and the CoNi LDH nanosheets can offer more electrochemical active sites for better faradaic reactions. Moreover, the core-shell heterostructure can also maintain the structural integrity during the processes of continuous charge/discharge. The MCS@CN LDH electrode displays a satisfactory specific capacitance of 1206 C g-1 and excellent cycling performance with ∼92% retention after 10 000 cycles. In addition, an asymmetric supercapacitor (ASC), in which MCS@CN LDH and N-doped rGO are used as the positive electrode and the negative electrode, was assembled which exhibits an energy density of 48.8 W h kg-1 with superior cycling stability, indicating the potential of this electrode in practical energy storage.

Fabrication of Silk Fibroin/Graphene Film with High Electrical Conductivity and Humidity Sensitivity.

Silk fibroin (SF) is a natural material with good biocompatibility and excellent mechanical properties, which are complementary to graphene with ultrahigh electrical conductivity. In this study, to maximally combine graphene and silk fibroin, a well-dispersed silk fibroin/graphene suspension was successfully prepared in a simple and effective way. Then we prepared a flexible conductive SF/graphene film with a minimum resistance of 72.1 ± 4.7 Ω/sq by the casting method. It was found that the electrical conductivity of the SF/graphene film was related to the water content of the film, and the variation was more than 200 times. Therefore, it will play an important role in the field of humidity sensors. It also has excellent mechanical properties in both wet and dry states. These unique features make this material a promising future in the fields of biomedical applications, wearable sensors, and implantable internal sensors.

Highly flexible and ultra-thin carbon-fabric/Ag/waterborne polyurethane film for ultra-efficient EMI shielding

We report in this work an ultra-thin and flexible carbon-fabric/Ag/waterborne polyurethane film (named CEF-NF/Ag/WPU film) that exhibits ultra-efficient EMI shielding property using electroless Ag plating combined with the enhanced-pressing process. The optimal CEF-NF/Ag/WPU film (0.183 mm) displays an ultra-high electrical conductivity of 11986.8 S/cm and a superior EMI-SE of 102.9 dB, which demonstrates the Ag deposition can effectively improve the electrical and EMI shielding performance. Compared with the film without an enhanced-pressing, the EMI-SE of a CEF-NF/Ag/WPU film with an enhanced-pressing showed an increase of about 37.5%. The porous structure deposited with Ag particles coating endows this composite film with remarkable EMI-SE at a thin thickness and lightweight (SSEt up to 5808.7 dB cm2 g−1) which outperforms most works. At last, this CEF-NF/Ag/WPU film performs outstanding reliability after ultrasound treatment, bending test and thermal reliability test. In summary, this film has great potential in the fields of wearable devices and flexible materials.

Extremely high conductivity observed in the triple point topological metal MoP

Weyl and Dirac fermions have created much attention in condensed matter physics and materials science. Recently, several additional distinct types of fermions have been predicted. Here, we report ultra-high electrical conductivity in MoP at low temperature, which has recently been established as a triple point fermion material. We show that the electrical resistivity is 6 nΩ cm at 2 K with a large mean free path of 11 microns. de Haas-van Alphen oscillations reveal spin splitting of the Fermi surfaces. In contrast to noble metals with similar conductivity and number of carriers, the magnetoresistance in MoP does not saturate up to 9 T at 2 K. Interestingly, the momentum relaxing time of the electrons is found to be more than 15 times larger than the quantum coherence time. This difference between the scattering scales shows that momentum conserving scattering dominates in MoP at low temperatures.

Advanced Reversible Long-Lasting Flexible Metal-Air Batteries Using Mn/Fe Hexaiminobenzene Metal-Organic Frameworks

Fast growing “Internet of Things” has an ever-increasing demand for advanced batteries with high energy density, robustness, flexibility, and environmental benignity for emerging high-tech electronic technologies, electric vehicles, and smart grids. Herein, we demonstrate robust aqueous and flexible ZABs employing three-dimensional dual-linked hexaiminobenzene metal-organic frameworks (Mn/Fe-HIB-MOF) as redox-active robust bifunctional electrocatalysts with ultrahigh intrinsic electrical conductivity and atomically tuned multi-shelled hollow spheres. Superionic functionalized bio-cellulose nanofibrous, solid-state membrane electrolyte (64 mS∙cm−1) is also presented with outstanding flexibility and water retention. The well-defined quintet-shelled hollow sphere MOFs possess a hierarchical porous structure, excellent packing density with a surface area of (2,298 m2.g-1), and chemical stability contrasted to conventional MOFs. The Mn/Fe-HIB-MOFs exhibited superior bifunctional oxygen electrocatalytic activity (0.627 V) with half-wave potential (0.883 V) for oxygen reduction and overpotential (280 mV @10 mA∙cm−2) for oxygen evolution reactions, outperforming commercial Pt/C and RuO2. The liquid and flexible ZABs with the present constituents revealed the world-record breaking cycling stability of 1,000 h (6,000 cycles) and 600 h (3,600 cycles) with fast fading and exceptionally high rate capacity (10 and 25 mA cm- 2), respectively, reported to date for rechargeable ZABs. These promising results illustrate great perspectives for sustainable rechargeable ZABs in the modern industries of electric vehicles and wearable electronics.

First-principles determination of the ultrahigh electrical and thermal conductivity in free-electron metals via pressure tuning the electron-phonon coupling factor

Responses of materials at high pressures can reveal fundamental insights into properties of condensed matter that are otherwise masked under ambient conditions. Using first-principles calculations to determine the electron-phonon interactions of free-electron metals at high pressures, we show that the electrical and thermal transport properties of aluminum, gold, and silver can be significantly enhanced with the application of high pressures. This is partly attributed to the decrease in electron-phonon coupling with increasing pressures. At elevated temperatures, under these high-pressure conditions, the thermal conductivity of aluminum is amongst the highest of any known material, surpassing the thermal conductivity of diamond at ambient pressure. Moreover, through calculation of the spectrally resolved electron-phonon coupling parameter at high pressures, we show an increased contribution to electron-phonon coupling from high-frequency longitudinal phonon modes scattering with electrons in aluminum. Using the same analysis with gold and silver, we show that low frequency acoustic phonon scattering with electrons is increased at high pressures. This work provides valuable insights into the electron-phonon scattering processes occurring under high pressures, which gives rise to new regimes of electrical and thermal transport properties in metals.

Ultrahigh Electrical Conductivity of Graphene Embedded in Metals

AbstractHighly efficient conductors are strongly desired because they can lead to higher working performance and less energy consumption in their wide range applications. However, the improvements on the electrical conductivities of conventional conductors are limited, such as purification and growing single crystal of metals. Here, by embedding graphene in metals (Cu, Al, and Ag), the trade‐off between carrier mobility and carrier density is surmount in graphene, and realize high electron mobility and high electron density simultaneously through elaborate interface design and morphology control. As a result, a maximum electrical conductivity three orders of magnitude higher than the highest on record (more than 3,000 times higher than that of Cu) is obtained in such embedded graphene. As a result, using the graphene as reinforcement, an electrical conductivity as high as ≈117% of the International Annealed Copper Standard and significantly higher than that of Ag is achieved in bulk graphene/Cu composites with an extremely low graphene volume fraction of only 0.008%. The results are of significance when enhancing efficiency and saving energy in electrical and electronic applications of metals, and also of interest for fundamental researches on electron behaviors in graphene.

Ultrathin nitrogen-doping graphene films for flexible and stretchable EMI shielding materials

Ultrathin, flexible and highly conductive materials that possess excellent electromagnetic interference (EMI) shielding performance are greatly needed, especially for the fabrication of stretchable shielding materials in practical applications such as wearable and foldable electronics. Graphene oxide (GO) sheets are modified with ethylenediamine to prepare cross-linked graphene films using a pressure-assisted self-assembly technique. FTIR and XPS results demonstrate that amine monomers are chemically bonded to GO sheets, with simultaneous reduction of GO sheets. After thermal annealing and followed with compression, the 6.6-μm-thick nitrogen-doping graphene film (rGO-EDA-2) is obtained with ultrahigh electrical conductivity of 8796 S cm−1. The excellent electrical conductivity is mainly attributed to nitrogen-doping effect, defects repair during chemical functionalization and removal of oxygenated groups. Ultrahigh electrical conductivity, multilayer structure and modified electronic structure with nitrogen doping lead to outstanding shielding performance for the rGO-EDA-2 film, with excellent shielding effectiveness (SE) of 58.5 dB and the specific SE/thickness of 43902 dB cm2 g−1, respectively. By fixing the rGO-EDA-2 film on the pre-stretched wavy substrate, the stretchable shielding composite is obtained, with constant EMI SE of 56.3 dB after repeated stretching. The pre-stretched wavy substrate allows the multilayer graphene film to achieve wavy structure after strain release, which is capable of bearing tensile strain up to 32.6%. This study could be significant in the applications of stretchable and wearable electronic devices.

Molten salt conversion of polyethylene terephthalate waste into graphene nanostructures with high surface area and ultra-high electrical conductivity

The pollution caused by the accumulation of plastic products is a serious emerging threat to the nature and to us. Here, we first report on the structural and thermokinetic characterization of the plastic bottle material. It was found that the pyrolysis of polyethylene terephthalate in air leads to the formation of an amourphose carbon with an exceptional thermal oxidation resistance, based on which an effective and scalable molten salt strategy for green conversion of plastic bottles into a highly conductive nanostructured carbon is proposed. In this process, no complicated equipment or protective gas is required. The nanostructured carbon consisted of crystalline graphitic nanosheets with a thickness of less than 10 nm; and an ultra-high electrical conductivity of 1150 S m−1 at a low bulk density of 1 g cm−3, with an estimated production cost about US $6 kg−1. These characteristics are attractive for various applications including conductive additives to electronic devices. In the light of the fact that the plastic pollution crisis cannot be appropriately resolved without the involvement of short term economic motivations, the proposed molten salt method may provide a sufficient economic driving force towards the use of PET wastes as valuable raw materials, hence protecting the environment.

Reading Contrast of Phase-Change Electrical Probe Memory in Multiple Bit Array

Reading contrast of phase-change electrical probe memory is investigated using a newly developed electrical switching model that accurately mimics the threshold switching of the phase-change media. Multiple bit array in either crystalline or amorphous phase is introduced into the model to take into account the influence of the readout cross-talk arising from inter-bit and inter-track interferences. Based on this configuration, the reading contrast is calculated by properly tailoring the electrical and geometrical properties of the capping, phase-change, and bottom layers as well as varying the length of the bit and track pitch. We found that the reading contrast can be significantly enhanced using an ultra-thin phase-change layer sandwiched by an ultra-thin capping layer with an intermediate electrical conductivity, and a relatively thick bottom layer with ultra-high electrical conductivity, as well as maintaining the length of the bit and track pitches similar to the size of the electrical probe. An optimized media stack that is also experimentally achievable from the state-of-the-art film deposition technologies is proposed, enabling a reading contrast of 0.85 for crystalline bit array and of 0.68 for amorphous bit array, close to those induced from isolated bit configuration immune to readout cross-talk. In order to thoroughly eliminate the adverse effect caused by readout cross-talk, the concept of patterned probe phase-change memory is introduced and its practicality for further alleviating the reading contrast is briefly discussed.

Chemical Simultaneous Synthesis Strategy of Two Nitrogen-Rich Carbon Nanomaterials for All-Solid-State Symmetric Supercapacitor.

Present work demonstrates a single step process for simultaneous synthesis of metal-nanoparticle-encapsulated nitrogen-doped bamboo-shaped carbon nanotubes (M/N-BCNTs) and graphitic carbon nitride (G-C3N3). The synthesis of two different carbon nanostructures in a single step is recognized for the first time. This process involves the use of inexpensive and nontoxic precursors such as melamine as carbon and nitrogen sources for the growth of G-C3N3 and M/N-BCNTs. In this technique, the utilization of unwanted gases such as ammonia and hydrocarbons released during the decomposition of melamine is the key to grow M/N-BCNTs over the catalyst along with the formation of G-C3N4. The implementation of M/N-BCNTs as the electrode material for all-solid-state symmetric supercapacitor results in a maximum specific capacitance of ∼368 F g–1 with excellent electrochemical stability with 97% capacity retention after 10 000 cycles. Furthermore, fabricated symmetric supercapacitor shows maximum high energy and power density up to 10.88 W h kg–1 and 2.06 kW kg–1, respectively. The superior electrochemical activity of M/N-BCNTs can be attributed to its high surface to area volume ratio, unique structural characteristics, ultrahigh electrical conductivity, and carrier mobility.

Ultrahigh-temperature conversion of biomass to highly conductive graphitic carbon

Graphitic carbon has attracted tremendous research interest in recent years owing to its exceptional thermal and electrical properties that arise from the ordered sp2 hybridized carbon structure. Due to its high activation energy, graphitization is often energy- and chemical-intensive. In addition, the electrical conductivity of graphitized materials has always been limited by the presence of intrinsic defects. In this paper, we propose a new method to convert lignin-based biomass into highly crystalline graphitic carbon by a Joule heating process. The Joule heating utilizes the internal resistance of a reduced graphene oxide/lignin (rGO-lignin) carbon film to heat the sample to up to 2500 K within 1 h. The annealing of lignin at this high temperature is found to remove impurities and intrinsic defects, as well as to initiate the graphitization process. Amorphous lignin carbon can be converted into short-range ordered and graphitic carbon with an ultrahigh electrical conductivity of 4500 S/cm, significantly higher than the original 6.4 S/cm. The microstructure change underlying this high electrical conductivity was further probed through electron microscopy and chemical analysis. This highly crystalline, electrically conductive graphitized lignin-carbon is expected to be useful for numerous applications where high conductivity and corrosion resistance are desired.

Graphene and carbon black filled conductive nanocomposite films for heating element applications

Graphene has ultra-high electrical and thermal conductivity, which makes graphene as the most encouraging fillers for thermally conductive composites. Graphene and/or carbon black filled conductive polymer composite (CPC) films used as heating element are smarter than the traditional heating elements due to less environmental pollution, ease of application on many surfaces and possess the merits of lightweight. In this study, we investigated mainly the production, characterization and industrial application of graphene/carbon black reinforced styrene acrylic copolymer emulsion matrix composite films deposited on polyvinyl chloride for flexible heating element. After that, the films were dried at room temperature for 24 h in air. Structural and surface properties of the CPC films were characterized by X-ray diffraction and scanning electron microscopy. Temperature, time and voltage relation of the produced composite films were investigated. Heating and electrical properties of the CPC films were determined by using a thermal camera and 4-point probe measurement system, respectively. The electrical resistivity of the CPC films decreases from ~ 108 to 101 Ω cm with increasing the filler content or using a combination of two fillers. Graphene and carbon black filled conductive polymer composites to be considered as candidates for flexible heating element applications exhibited good electrical and heating properties thanks to synergistic effect of fillers.

Layer-Structured Design and Fabrication of Cyanate Ester Nanocomposites for Excellent Electromagnetic Shielding with Absorption-Dominated Characteristic.

In this work, we propose novel layer-structured polymer composites (PCs) for manipulating the electromagnetic (EM) wave transport, which holds unique electromagnetic interference (EMI) shielding features. The as-prepared PCs with a multilayered structure exhibits significant improvement in overall EMI shielding effectiveness (EMI SE) by adjusting the contents and distribution of electrical and magnetic loss fillers. The layer-structured PCs with low nanofiller content (5 wt % graphene nanosheets (GNSs) and 15 wt % Fe3O4) and a thickness of only 2 mm exhibited ultrahigh electrical conductivity and excellent EMI SE, reaching up to 2000 S/m and 45.7 dB in the X-band, respectively. The increased EMI SE of the layer-structured PCs was mainly based on the improved absorption rather than the reflection of electromagnetic waves, which was attributed to the “absorb-reflect-reabsorb” process for the incident electromagnetic waves. This work may provide a simple and effective approach to achieve new EMI shielding materials, especially for absorption-dominated EMI shielding.

A New Anode for Lithium-Ion Batteries Based on Single-Walled Carbon Nanotubes and Graphene: Improved Performance through a Binary Network Design.

Carbon nanomaterials, especially graphene and carbon nanotubes, are considered to be favorable alternatives to graphite-based anodes in lithium-ion batteries, owing to their high specific surface area, electrical conductivity, and excellent mechanical flexibility. However, the limited number of storage sites for lithium ions within the sp2 -carbon hexahedrons leads to the low storage capacity. Thus, rational structure design is essential for the preparation of high-performance carbon-based anode materials. Herein, we employed flexible single-walled carbon nanotubes (SWCNTs) with ultrahigh electrical conductivity as a wrapper for 3D graphene foam (GF) by using a facile dip-coating process to form a binary network structure. This structure, which offered high electrical conductivity, enlarged the electrode/electrolyte contact area, shortened the electron-/ion-transport pathways, and allowed for efficient utilization of the active material, which led to improved electrochemical performance. When used as an anode in lithium-ion batteries, the SWCNT-GF electrode delivered a specific capacity of 953 mA h g-1 at a current density of 0.1 A g-1 and a high reversible capacity of 606 mA h g-1 after 1000 cycles, with a capacity retention of 90 % over 1000 cycles at 1 A g-1 and 189 mA h g-1 after 2200 cycles at 5 A g-1 .

Superelastic and multifunctional graphene-based aerogels by interfacial reinforcement with graphitized carbon at high temperatures

Although lightweight and three-dimensional graphene aerogels and foams combining ultrahigh electrical conductivity, superelasticity and fatigue resistance are highly desirable for widespread applications, it remains a large challenge to construct a multifunctional framework affording the rapid electron transport and efficient load transfer due to the weak interfaces between highly reduced graphene oxide sheets. Herein, we report an efficient approach for fabricating an integrated graphene aerogel by bridging its reduced graphene oxide sheets with polyimide macromolecules followed by graphitization at 2800 °C. During the graphitization process, the reduced graphene oxide sheets are thermally reduced to graphene efficiently by removing their residual oxygen-containing groups and healing their defects, while the polyimide component is graphitized to turbostratic carbon to bridge the graphene sheets, resulting in an integrated graphene aerogel with satisfactory mechanical and functional performances, including ultrahigh electrical conductivity (>1000 S m−1) at a low density, unprecedented high electromagnetic interference shielding effectiveness of ∼83 dB in X-band, 90% reversible compressibility, and reliable resistance to fatigue for 1000 compressive cycles at 50% strain. The integrated graphene aerogels with such multifunctional performances hold a great promise for applications as electromagnetic interference shielding materials, oil adsorbents, and conductive scaffolds for polymer nanocomposites.