Conductive Carbon Layer Research Articles

A 3D Trilayered CNT/MoSe2/C Heterostructure with an Expanded MoSe2 Interlayer Spacing for an Efficient Sodium Storage

AbstractFreestanding composite structures with embedded transition metal dichalcogenides (TMDCs) as the active material are highly attractive in the development of advanced electrodes for energy storage devices. Most 3D electrodes consist of a bilayer design involving a core–shell combination. To further enhance the gravimetric and areal capacities, a 3D trilayer design is proposed that has MoSe2 as the TMDC sandwiched in‐between an inner carbon nanotube (CNT) core and an outer carbon layer to form a CNT/MoSe2/C framework. The CNT core creates interconnected pathways for the e−/Na+ conduction, while the conductive inert carbon layer not only protects the corrosive environment between the electrolyte and MoSe2 but also is fully tunable for an optimized Na+ storage. This unique heterostructure is synthesized via a solvothermal‐carbonization approach. Due to annealing under a confined structural configuration, MoSe2 interlayer spaces are expanded to facilitate a faster Na+ diffusion. It is shown that an ≈3 nm thick carbon layer yielded an optimized anode for a sodium‐ion battery. The 3D porosity of the heterostructure remains intact after an intense densification process to produce a high areal capacity of 4.0 mAh cm−2 and a high mass loading of 13.9 mg cm−2 with a gravimetric capacity of 347 mAh g−1 at 500 mA g−1 after 500 cycles.

Improving the performance of sulphur doped LiMn2O4 by carbon coating

Sulphur-doped spinel LiMn2O3.99S0.01 is a promising cathode material for lithium-ion batteries. It can be obtained in a form of nanocrystals by a facile, eco-friendly and water-based sol-gel synthesis. In this work, LMOS was successfully coated with a 2–3 nm conductive carbon layer fabricated from pyrolysis of modified poly(N-vinylformamide) - water-soluble polymer precursor. Carbon coated material exhibits greatly increased performance under high currents and improved cyclability in long-term charge-discharge tests. Pristine and carbon-coated samples are characterized by X-ray diffraction, thermogravimetric analysis, elemental analysis, transmission electron microscopy and X-ray photoelectron spectroscopy. Electrochemical performance of the materials is examined by galvanostatic charge-discharge tests, cyclic voltammetry and electrochemical impedance spectroscopy. Carbon coated sample present a highly enhanced rate capability, withstanding up to 100C rate and maintaining up to 67.5% of initial 1C discharge capacity at 50C rate (1C - 148 mA g−1 – current required to fully charge a cell in time of 1 h). Li+ ion apparent diffusion coefficient in carbon coated sample is approximately twice increased. Electrochemical impedance spectroscopy has shown, that carbon coating decreases internal resistances of the cell caused by material passivation and charge-transfer reactions.

Amorphous Ni/C nanocomposites from tandem plasma reaction for hydrogen evolution

There is a growing interest in the nanostructure of metal nanoparticles encapsulated in carbon shells (M/C) to act as cost-effective and high-performance electrocatalysts for hydrogen production. Despite tremendous efforts, large-scale and controllable production of highly-active M/C nanocomposites for electrocatalysis remains a great challenge. Herein, we report a tunable and general strategy tandem plasma reaction (TPR) for manufacturing a series of carbon encapsulated Ni/C nanocomposites with different compositions. Benefiting from the synergistic effect between the conductive carbon layer and Ni nanoparticles, the electrocatalytic performance can be adjusted to an optimal state. A volcano shape dependence between electrocatalytic activity and the percentage of carbon is presented experimentally. With the simplicity and intelligence of the approach, the strategy based on tandem plasma reaction presents great potential to the preparation of extendable metal/carbon nanocomposites for versatile applications.

Enhanced pseudocapacitive energy storage properties of Nb 2 O 5 /C core‐shell structures with the surface modification

Pseudocapacitive energy storage is an attractive technology as it can achieve high energy density at high rate conditions. However, its practical application has been an issue because of low electrical conductivity of nanoscale electrode materials. Surface coating is an effective way to enhance the electrochemical properties of the electrochemical energy storage system by helping electron transfer between the electrode material and current collector. In order for surface coating technologies to be applied to pseudocapacitive energy storage field, providing fast ions and electrolyte transport through the coating layer as well as high electrical conductivity is essential because pseudocapacitors aim for high rate charge/discharge capability. In this paper, the Nb2O5/carbon core-shell structure is developed to meet these requirements. Simple microwave-assisted method is applied to create nanoscale (approximately 5 nm) conductive carbon layer on the surface of bare Nb2O5 nanoparticles, and the high power capability of Nb2O5/carbon core-shell is improved further by oxidation process providing open structure for electrolyte and ion diffusion. Thick electrode architecture containing oxidized Nb2O5/carbon core-shell shows superior high rate performance as capacities of 215 C g−1 are obtained at a 50 mV s−1 scan rate.

Design and synthesis of sandwich-like CoNi2S4@C@NiCo-LDH microspheres for supercapacitors

Novel sandwich-like hollow nickel cobalt sulfides@carbon@nickel cobalt double hydroxides (CoNi2S4@C@NiCo-LDH) are synthesized using a facile microwave-assisted hydrothermal method and investigated as promising electrode materials for supercapacitors. The in-between highly conductive carbon layer simultaneously serves as uniform cover for CoNi2S4 and large-area support for ultrathin NiCo-LDH, which can restrain the microstructure change during the cyclic charge-discharge process and enhance the transmission rate of electrons and electrolyte ions. The especially nanostructured CoNi2S4@C@NiCo-LDH nanocomposites exhibit outstanding supercapacitive performances including excellent gravimetric specific capacitance (1183 mAh g−1 at 1 A g−1) and high rate capability (85.8% retention rate at 20 A g−1). More importantly, the assembled CoNi2S4@C@NiCo-LDH//graphene asymmetric supercapacitor can deliver a superhigh specific capacitance of 550 mAh g−1 at 1 A g−1, prominent energy density of 111.9 Wh kg−1 and long cycling stability with 93.8% of its initial capacitance after 10,000 cycles at 5 A g−1.

Manganese oxides/N-doped carbon particles with high capacity retention for aqueous rechargeable zinc battery

Manganese dioxide as the electrode for aqueous zinc-ion batteries (AZIBs) is influenced by the material dissolution. Herein, β-MnO2/N-doped carbon matrix (NCm) or Mn5O8/NCm composites were fabricated by effective synthesis process using polyaniline (PANI) as carbon/nitrogen sources. The conductive N-doped carbon layer was tied to β-MnO2, which increased the electrical conductivity of the β-MnO2 nanorod. At current densities of 200 mA g−1, the β-MnO2/NCm electrode delivered a higher discharge capacity of 331 mAh g−1 comparing with 185 mAh g−1 for the pure β-MnO2 electrode. Besides, the Mn5O8/NCm electrode could provide a discharge capacity of 266 mAh g−1. Therefore, the approach in this study may pave the way on preparing manganese oxides/NCm materials for AZIBs.

Assistive Electro Discharge Machining of AIN Ceramics

Electro discharge machining process experiences limitation due to the non-conductive nature of the workpiece material. However, researchers proposed assistive EDM technique to machine nonconductive materials in the past. These assistive techniques require a minimal thickness of 100 µm conductive coating on the workpiece surface which usually takes longer time to coat the surface using PVD (physical vapor deposition) method. In this paper, a new modified assistive EDM method has been proposed to machine nonconductive Aluminum Nitride ceramics successfully. A three layers coating was used that included silver coating, carbon tape and silver nano-powder on a non-conductive aluminium nitride. This coating aids in conducting EDM operation due to the availability of conductive particles. Apart from the decomposition of dielectric that facilitates carbon particles on top of conductive carbon layer, coating itself also contributes in conductive silver particles. Therefore, carbon as well as silver debris that remains on the ceramics surface aids in continuous spark generation which in turn creates alternative thermal load and thus removes materials.

Bottom-Up Construction of Reduced-Graphene-Oxide-Anchored MnO with an Nitrogen-Doped Carbon Coating for Synergistically Improving Lithium-Ion Storage.

Designing an advanced architecture to overcome the innate issue of MnO-based anode materials in terms of low electrical conductivity and severe volume change during cycling is still a challenge toward which more effort needs devoted. Here, an intriguing hybrid involving the architecture of reduced graphene oxide (RGO)-anchored MnO within an nitrogen-codoped carbon coating (RGO-MnO@NC) is reported via a simple and facile approach and regarded as a promising lithium-ion (Li+) anode material with high rate capacity, large specific capacity, and a long cycle lifespan simultaneously. The resulting porous conductive carbon layer could not only promote the electron/ion transfer but also alleviate the volume variation for retaining a relatively stable solid electrolyte interphase and prevent MnO from direct contact with the electrolyte to reduce unexpected lithium consumption. The existing internal voids offer the space to accommodate volume expansion in the lithiation/delithiation processes, and RGO could build a large conductive network for better electron transfer. Consequently, the RGO-MnO@NC electrode presents high Li+ storage capacity (699 mAh g-1 at 0.1 A g-1), excellent cycling performance (607 mAh g-1 at 1 A g-1 over 550 cycles), and a remarkable rate performance. Through kinetic analysis, it is revealed that RGO-MnO@NC exhibits an enhanced capacitive contribution for Li+ storage, showing a typical faradaic surface pseudocapacitive mechanism. This work proposes a new strategy to ameliorate the deficiency of the electrode material toward the conductivity and volume change for enhanced Li+ storage.

A simple fabrication route of porous palladium/palladium oxide/carbon nanostructures using one-step combustion waves for high-performance pH sensors

Reduction-oxidation controls and synthesis of organic-inorganic hybrid structures are key features associated with their electrochemical properties. However, they involve bulky setup and long-time processes that incur high-cost. Herein, we report one-step combustion waves (CWs) for the fabrication of hybrid-porous palladium/palladium oxides/carbon (Pd/PdxOy@C) nanostructures with controllable atomic composition and their application as a high-performance pH sensor. Hybrid composites of Pd/formaldehyde (FA)/nitrocellulose (NC) were prepared as precursors. Self-propagating CWs through the NC networks carried out the transformation from Pd to PdO2 in the higher oxidation state and the formation of a carbon layer, while the fast release of chemicals in CWs developed the porous nanostructures with large surface areas. The flexible pH sensor using the synthesized Pd/PdxOy@C powders exhibited the outstanding specific voltage potential (2.08 V/mg at pH 2.83) and sensitivity (167 mV/mg pH). It showed no hysteresis during cycling of pH values and high stability over 4 h (voltage change <0.89%). The high oxidation states and conductive carbon layers of Pd/PdxOy@C with large surface areas improved the specific potential and the stability in minute changes of pH values and forward-reverse proton exchanges. The physicochemical synthesis using CWs would contribute to developing scalable processing for electrochemical applications, including chemical sensors.

Fabrication of noble-metal-free CdS nanorods-carbon layer-cobalt phosphide multiple heterojunctions for efficient and robust photocatalyst hydrogen evolution under visible light irradiation

Abstract Photocatalytic water splitting has aroused great interest as a clean and renewable energy conversion process. In this study, we prepared a novel noble-metal-free multiple heterojunction photocatalyst (CdS@C-CoP) composed of CdS nanorods, conducting carbon layer and CoP nanoparticles cocatalyst for the first time. The obtained CdS@C-CoP composites exhibited excellent performance and stability under visible light irradiation when it was used as photocatalysts for hydrogen evolution. For the optimum CdS@C-CoP sample, an average hydrogen evolution rate reached up to 10089 μmol g−1 h−1, nearly 6 fold as high as that of pure CdS. The enhanced photocatalytic hydrogen production rate can be ascribed to the synergistic effect between conductive carbon layer and surface cocatalyst CoP, which resulted in efficient separation of photoexcited charge carriers and abundant active sites for hydrogen reduction. This work presented a novel way to design composite photocatalyst with efficient hydrogen generation properties through combining two kinds of surface modification methods: thin carbon layer coating and surface cocatalysts loading.

The Influence of the Work Function of Hybrid Carbon Electrodes on Printable Mesoscopic Perovskite Solar Cells

In printable mesoscopic perovskite solar cells (PSCs), carbon electrodes play a significant role in charge extraction and transport, influencing the overall device performance. The work function and electrical conductivity of the carbon electrodes mainly affect the open-circuit voltage (VOC) and series resistance (Rs) of the device. In this paper, we propose a hybrid carbon electrode based on a high-temperature mesoporous carbon (m-C) layer and a low-temperature highly conductive carbon (c-C) layer. The m-C layer has a high work function and large surface area and is mainly responsible for charge extraction. The c-C layer has a high conductivity and is responsible for charge transport. The work function of the m-C layer was tuned by adding different amounts of NiO, and at the same time, the conductivities of the hybrid carbon electrodes were maintained by the c-C layer. It was supposed that the increase of the work function of the carbon electrode can enhance the VOC of printable mesoscopic PSCs. Here, we...

Self-Assembly of Antisite Defectless nano-LiFePO4 @C/Reduced Graphene Oxide Microspheres for High-Performance Lithium-Ion Batteries.

LiFePO4 @C/reduced graphene oxide (rGO) hierarchical microspheres with superior electrochemical activity and a high tap density were first synthesized by using a Fe3+ -based single inorganic precursor (LiFePO4 OH@RF/GO; RF=resorcinol-formaldehyde, GO=graphene oxide) obtained from a template-free self-assembly synthesis followed by direct calcination. The synthetic process requires no physical mixing step. The phase transformation pathway from tavorite LiFePO4 OH to olivine LiFePO4 upon calcination was determined by means of the in situ high-temperature XRD technique. Benefitting from the unique structure of the material, these microspheres can be densely packed together, giving a high tap density of 1.3 g cm-3 , and simultaneously, defectless LiFePO4 primary nanocrystals modified with a highly conductive surface carbon layer and ultrathin rGO provide good electronic and ionic kinetics for fast electron/Li+ ion transport.

Effect of Electric Field on Ion Transport in Nanoporous Membranes with Conductive Surface

The effect of an external electric field on the ionic conductivity and selective properties of ceramic membranes based on alumina nanofibers coated with a conductive carbon layer has been studied. It has been shown that the membranes are ideally polarizable in the polarizing voltage range of −500 to +500 mV and, therefore, can be used for implementing switchable ionic selectivity. Experiments have revealed that the membrane resistance decreases with a change in the applied potential from 0 to ±500 mV. It has been shown that the membrane selectivity can be switched from anion to cation by varying the external potential. The surface charge density of the membranes has been determined in terms of the Teorell–Meyer–Sievers model according to the experimental measurements of the membrane potential.

Progress and prospect for NASICON-type Na3V2(PO4)3 for electrochemical energy storage

Abstract Sodium-ion batteries (SIBs) have attracted increasing attention in the past decades, because of high overall abundance of precursors, their even geographical distribution, and low cost. Na3V2(PO4)3 (NVP), a typical sodium super ion conductor (NASICON)-based electrode material, exhibits pronounced structural stability, exceptionally high ion conductivity, rendering it a most promising electrode for sodium storage. However, the comparatively low electronic conductivity makes the theoretical capacity of NVP cannot be fully accessible even at comparatively low rates, presenting a major drawback for further practical applications, especially when high rate capability is especially important. Thus, many endeavors have been conformed to increase the surface and intrinsic electrical conductivity of NVP by coating the active materials with a conductive carbon layer, downsizing the NVP particles, combining the NVP particle with various carbon materials and ion doping strategy. In this review, to get a better understanding on the sodium storage in NVP, we firstly present 4 distinct crystal structures in the temperature range of − 30°C∼225°C namely α-NVP, β-NVP, β′-NVP and γ-NVP. Moreover, we give an overview of recent approaches to enhance the surface electrical conductivity and intrinsic electrical conductivity of NVP. Finally, some potential applications of NVP such as in all-climate environment and PHEV, EV fields have been prospected.

Three-dimensional NaTi2(PO4)3@C microsphere as a high-performance anode material for advanced sodium-ion batteries

Herein, three-dimensional NaTi2(PO4)3@C microsphere (denoted as 3D-NaTi2(PO4)3@C) has been designed and fabricated for the first time by using a facile spray-drying method. The well-crystallized 3D-NaTi2(PO4)3@C composite is formed by calcination at 800 °C under Ar atmosphere. The 3D microspheres with particle size of about 4 μm are assembled from 120 nm nanosized grains. As an anode material for sodium-ion batteries, the 3D-NaTi2(PO4)3@C composite exhibits good rate capability and long-cycle life due to the small NaTi2(PO4)3 nanocrystals and conductive carbon layer. It can deliver a reversible capacity of 126.6 mAh g−1 at 0.1C and show a capacity decay rate of <8% when cycled under the high rate of 10C for 500 cycles. These results demonstrate that the as-fabricated 3D-NaTi2(PO4)3@C material is a promising anode material for high-performance sodium-ion batteries.

Enhanced visible light activated hydrogen evolution activity over cadmium sulfide nanorods by the synergetic effect of a thin carbon layer and noble metal-free nickel phosphide cocatalyst

Photocatalytic water splitting is considered to be a promising strategy for addressing the global energy crisis through the expanded use of solar energy. Herein, cadmium sulfide (CdS) nanorods modified with a thin conductive carbon layer and a nickel phosphide co-catalyst, referred to as cadmium sulfide coated with a carbon layer and nickel phosphide (CdS@C/Ni2P, where @ indicates a core–shell structure), were synthesized and applied as a novel composite photocatalyst for water splitting. The optimized CdS@C/Ni2P composite showed a high photocatalytic hydrogen generation rate of 32030 μmol h−1 g−1, which was approximately 19 times as high as that of pure CdS. We believed that the thin carbon layer acted as an electron acceptor to promote charge transfer and protect the CdS nanorods from photocorrosion. In addition, the surface loading of the nickel phosphide (Ni2P) cocatalyst was able to further draw photogenerated electrons from the cadmium sulfide coated with a carbon layer (CdS@C) heterojunction and provide active sites for hydrogen evolution. Thus, greatly enhanced hydrogen generation was achieved through a combination of carbon coating and surface cocatalyst loading. This development provides a new way to design composite photocatalysts with multiple junctions for efficient water splitting performance.

Stability of Li2MSiO4 (M = Mn, Co) in the carbon coating process

The stability of Li2MnSiO4 (LMS) and Li2CoSiO4 (LCS) in the conducting carbon layer (CCL)/Li2MSiO4 (M = Mn, Co) composites forming process was characterized in this paper. Studied nanocomposites were obtained via modified sol-gel Pechinis synthesis followed by the direct deposition of carbon coating on the active material grains. As a carbon precursor the poly-N-vinylforamide (PNVF) modified by pyromellitic acid (PMA) in water solution was used. The investigated materials were examined in terms of physicochemical properties by using the powder X-ray diffraction (XRD), and electrical conductivity studies (EC). The electrochemical properties of Li/Li+/CCL/Li2MnSiO4 cells were determined by the galvanostatic charge discharge tests (CELL TESTS). The stability of LMS and LCS under oxidizing and reductive conditions were analyzed by the temperature programmed oxidation (TPO/TG) and temperature-programmed reduction with H2 (H2-TPR). Results showed that CCL formation can be executed with reconstruction of LMS crystalline structure while it is impossible on LCS grains using standard pyrolysis. Given galvanostatic charging/discharging tests demonstrate that forming carbon coatings, with ca. 10 wt% carbon on polysilicate substrates can provide satisfactory electrical properties as well as enhanced surface stability.

Facile high-voltage sputtering synthesis of three-dimensional hierarchical porous nitrogen-doped carbon coated Si composite for high performance lithium-ion batteries

Various kinds of efforts have been devoted to ameliorate the serious volume-expansion effect and low electron conductivity of silicon-based materials in lithium ion batteries. Here, we report a facile high voltage sputtering process to prepare three-dimensional hierarchical porous nitrogen-doped carbon coated Si microsphere to significantly improve the lithium storage performance. The structure and morphology of the as-obtained samples are characterized by X-ray diffraction, transmission electron microscope and scanning electron microscope. The results indicate that the as-prepared composite is composed of silicon nanoparticles (∼100 nm) coated with conductive thin carbon layer (∼8.5 nm). The composite shows excellent lithium storage performance with a reversible capacity of 1565 mAh g−1 after 100 cycles at a current density of 0.5 A g−1, as well as a long cycling performance at the high current density of 2 A g−1. The facile preparation process and highly silicon-loading (∼78%) makes the prepared material be a great potential application in lithium-ion batteries.

Investigation of carbon coating approach on electrochemical performance of Li4Ti5O12/C composite anodes for high-rate lithium-ion batteries

Submicron-sized Li4Ti5O12/C (LTO/C) composites were successfully synthesized by using one-step and two-step route, in which sucrose was used as carbon precursor, and employed as anode materials for lithium-ion batteries (LIBs). The structure, surface morphology, and chemical compositions were characterized by X-ray diffraction, Raman spectroscopy, scanning, and transmission electron microscopy techniques. The electrochemical properties of the carbon-coated samples were examined by using the charge/discharge tests, cyclic voltammetry, and electrochemical impedance spectroscopy. It was found that the LTO/C synthesized by one-step method (designated as LTO/C-O) possessed smaller LTO/C particle size, more cohesive particle distribution, and more uniform conductive carbon layer on LTO surface compared with that synthesized by two-step method (LTO/C-T). As a result, the LTO/C-O electrode illustrated a high discharge capacity of 173.6 mAh g−1 at a charge/discharge rate of 0.1 C. Moreover, the discharge capacity retention of the LTO/C-O electrode can effectively deliver to 95.9, 90.9, 87.9, and 80.9%, whereas the LTO/C-T electrode exhibited 94.0, 79.9, 68.0, and 50.1% at 1, 5, 10, and 20 C, respectively. Therefore, the LTO/C-O can be considered as one of the promising anode materials for high-rate LIBs.

Three-Dimensional Hierarchical Structure ZnO@C@NiO on Carbon Cloth for Asymmetric Supercapacitor with Enhanced Cycle Stability.

In this work, we synthesized the hierarchical ZnO@C@NiO core-shell nanorods arrays (CSNAs) grown on a carbon cloth (CC) conductive substrate by a three-step method involving hydrothermal and chemical bath methods. The morphology and chemical structure of the hybrid nanoarrays were characterized in detail. The combination and formation mechanism was proposed. The conducting carbon layer between ZnO and NiO layers can efficiently enhance the electric conductivity of the integrated electrodes, and also protect the corrosion of ZnO in an alkaline solution. Compared with ZnO@NiO nanorods arrays (NAs), the NiO in CC/ZnO@C@NiO electrodes, which possess a unique multilevel core-shell nanostructure exhibits a higher specific capacity (677 C/g at 1.43 A/g) and an enhanced cycling stability (capacity remain 71% after 5000 cycles), on account of the protection of carbon layer derived from glucose. Additionally, a flexible all-solid-state supercapacitor is readily constructed by coating the PVA/KOH gel electrolyte between the ZnO@C@NiO CSNAs and commercial graphene. The energy density of this all-solid-state device decreases from 35.7 to 16.0 Wh/kg as the power density increases from 380.9 to 2704.2 W/kg with an excellent cycling stability (87.5% of the initial capacitance after 10000 cycles). Thereby, the CC/ ZnO@C@NiO CSNAs of three-dimensional hierarchical structure is promising electrode materials for flexible all-solid-state supercapacitors.