Nanocarbon Network Research Articles

Single atomic cobalt catalyst significantly accelerates lithium ion diffusion in high mass loading Li2S cathode

It is widely accepted that catalysts in batteries can decrease the energy barriers of conversion reactions. However, little attention has been paid to their influence on ionic diffusion in the electrode or across the interface. Herein, we report that lithium ion diffusivity can be significantly accelerated in an intrinsically electrode by atomically-distributed metal catalyst. Electrochemical measurements have found single atomic cobalt catalyst embedded in a nanocarbon network is capable of increasing the kinetics of lithium ion, providing rapid conversion reaction rate in an ultrahigh-rate Li2S battery. Meanwhile, density functional theory simulations have revealed that the lithium ion diffusion barrier on a nanocarbon surface is highly sensitive to the dopant atoms and can be decreased by introduction of cobalt atoms. The synergetic effects of the well-known Li2S decomposition catalysis and the lithium ion diffusion acceleration allow us to achieve a high Li2S mass loading cathode with superior rate performance and reversibility. The as-prepared Li2S electrode converted from cheap Li2SO4 precursors can deliver a high rate capacity (441 ​mA ​h ​g-1 based on Li2S at 10 ​C) and long lifespan for 1500 cycles at 2 ​C with average capacity fading of 0.04% per cycle. Impressively, the high areal mass loading cells display a specific capacity of 340 ​mA ​h ​g-1 based on Li2S mass at 23.4 ​mA ​cm-2 (5 ​C) and a long cycle life (2.26 ​mA ​h ​cm-2 at 6.77 ​mA ​cm-2 after 200 cycles), which have not been reported for Li2S cathodes.

Porous Graphene-like Carbon from Fast Catalytic Decomposition of Biomass for Energy Storage Applications.

A novel carbon material made of porous graphene-like nanosheets was synthesized from biomass resources by a simple catalytic graphitization process using nickel as a catalyst for applications in electrodes for energy storage devices. A recycled fiberboard precursor was impregnated with saturated nickel nitrate followed by high-temperature pyrolysis. The highly exothermic combustion of in situ formed nitrocellulose produces the expansion of the cellulose fibers and the reorganization of the carbon structure into a three-dimensional (3D) porous assembly of thin carbon nanosheets. After acid washing, nickel particles are fully removed, leaving nanosized holes in the wrinkled graphene-like sheets. These nanoholes confer the resulting carbon material with ≈75% capacitance retention, when applied as a supercapacitor electrode in aqueous media at a specific current of 100 A·g–1 compared to the capacitance reached at 20 mA·g–1, and ≈35% capacity retention, when applied as a negative electrode for lithium-ion battery cells at a specific current of 3720 mA·g–1 compared to the specific capacity at 37.2 mA·g–1. These findings suggest a novel way for synthesizing 3D nanocarbon networks from a cellulosic precursor requiring low temperatures and being amenable to large-scale production while using a sustainable starting precursor such as recycled fiberwood.

Black Titania with Nanoscale Helicity

AbstractThe fabrication of mesoporous black titanium dioxide (TiO2−x ) with a chiral nematic organization of core–shell nanorods is reported. Chiral templating of TiO2 nanoparticles onto gelatin‐functionalized cellulose nanocrystals (CNCs) followed by calcination yields carbonized TiO2/CNC helical materials that recover white TiO2 replicas after carbon removal. The hydrothermal surface reduction of the traditional white TiO2 by ascorbic acid affords freestanding chiral nematic black TiO2−x. The black TiO2−x is a visible light active semiconducting mesoporous structure constructed by chiral nematic crystalline–amorphous TiO2 core–shell nanorods. The chiral black TiO2−x nanoparticles supported on mesoporous nanocarbon networks are evaluated as lithium‐ion battery anode electrodes. Beyond the current efforts, these black TiO2−x materials and their composites may be useful in the fields of energy storage and catalysis.

Enhanced electrical conductivity of alumina/nano-carbon ceramic composite via iodine impregnation of gel-casted alumina body and reductive sintering

In this work, we present the fabrication of alumina/nano-carbon ceramic composite displaying enhanced electrical conductivity through facile iodine impregnation of gel-casted alumina body. Following the previously developed novel fabrication process of alumina/nano-carbon composite having a highly uniform nano-carbon network and superior semi-conductive properties via reductive sintering of gel-casted alumina body under inert atmosphere, we extended the process through the facile impregnation of gel-casted body in iodine solution resulting in enhancement of the amount of nano-carbon, graphitization degree, electrical conductivity and carrier density. The effect of iodine concentration on the properties of alumina/nano-carbon as well as the mechanism for enhanced electrical performance are also systematically investigated.

Charge Carrier Dynamics in Metal-Oxide/Nanocarbon Hybrid Photoelectrodes

One of the most critical challenges of the 21st century is the shift in energy use from fossil fuels to renewable sources. Photoelectrochemical solar energy conversion, as a potentially attractive candidate, has gained an increased momentum during the recent years. Although both water-splitting (hydrogen evolution) and carbon dioxide reduction are promising avenues, they both have substantial shortcomings to be addressed. A common virtue of these two processes is that a good photoelectrode has to concurrently fulfill many attributes to drive these reactions efficiently. One of the most important is the efficient charge carrier transport, which ensures that most of the photogenerated charge carriers can be extracted both toward the electrode/electrolyte junction and toward the back contact. Numerous promising photoelectrode material showed poor performance due to extensive charge carrier recombination both in the bulk and at the surface. A well-known example is α-Fe2O3 (hematite), in which the hole-diffusion length is only 2-4 nm.1 One possible way to improve charge carrier transport properties is to deposit the metal-oxide on an interconnected nanocarbon network (e.g., carbon nanotubes or graphene). These highly conductive nanoscaffolds can improve the transport of the photogenerated charge carriers, which in turn, results in an enhanced photoelectrochemical performance.2 In my presentation, I am going to discuss how charge carrier dynamics of various hematite and hematite/nanocarbon composites is affected by the composition of the nanohybrids and by the applied bias. Hematite/nanocarbon photoelectrodes were synthesized by a two-step method: first the nanocarbon layer was spray-coated on the surface of the substrate electrode, and the nanostructured metal-oxide component was electrodeposited in a subsequent step. The metal-oxide/nanocarbon ratio was precisely controlled by the deposition charge density. To investigate charge carrier dynamics on a timescale ranging from seconds to femtoseconds three different techniques were employed: (i) transient absorption spectroscopy, employing a fs pump-probe setup, (ii) intensity-modulated photocurrent spectroscopy, and finally (iii) fast chronoamperometry. By covering this broad timescale, it was possible to study charge carrier transport, trapping and recombination processes, which were greatly affected by both the applied potential and the presence of the nanocarbons. 1 Energy Environ. Sci., 2016, 9, 2744—2775. 2 J. Am. Chem. Soc. 2017, 139, 6682−6692.

Electrospun Kraft Lignin/Cellulose Acetate-Derived Nanocarbon Network as an Anode for High-Performance Sodium-Ion Batteries.

An innovative nanocarbon network material was synthesized from electrospun kraft lignin and cellulose acetate blend nanofibers after carbonization at 1000 °C in a nitrogen atmosphere, and its electrochemical performance was evaluated as an anode material in sodium-ion batteries. Apart from its unique network architecture, introduced carbon material possesses high oxygen content of 13.26%, wide interplanar spacing of 0.384 nm, and large specific surface area of 540.95 m2·g-1. The electrochemical test results demonstrate that this new nanocarbon network structure delivers a reversible capacity of 340 mA h·g-1 at a current density of 50 mA·g-1 after 200 cycles and exhibits a high rate capacity by delivering a capacity of 103 mA h·g-1 at an increased current density of 400 mA·g-1. The present work rendered an innovative approach for preparing nanocarbon materials for energy-storage applications and could open up new avenues for novel nanocarbon fabrication from green and environmentally friendly raw materials.

Healable, Flexible Supercapacitors Based on Shape Memory Polymers

Supercapacitors as novel and efficient energy storage devices could provide a higher power density and energy density compared to other electronics and devices. However, traditional supercapacitors are readily damaged, which leads to degraded performance or even failure. To make them more durable and efficient, healable flexible shape memory-based supercapacitors were unprecedentedly explored by a transfer process, in which the conductive nano-carbon networks were decorated with pseudocapacitance materials, followed by embedding them into a shape memory polymer matrix containing healing reagents. The composite exhibited flexibility, supercapacitance and self-healing capability originating from the shape memory effect and healing reagent. The morphologies, thermal, mechanical and capacitive properties, and the self-healability of the composite were investigated. In particular, the influence of the compositions on the healing efficiency was considered. The optimized composite exhibited good capacitance (27.33 mF cm−1), stability (only 4.08% capacitance loss after 1500 cycles) and healable property (up to 93% of the healing efficiency). The findings demonstrated how to endow the flexible polymeric electronics with healable bio-mimetic properties and may greatly benefit the application of intelligent polymers in the field of multi-functional electrical materials.

Nanocarbon/polyethylene composites with segregated conductive network for electromagnetic interference shielding

Nanocarbon/polyethylene (PE) composites filled with up to 10 vol.% of single filler, graphite nanoplatelets (GNPs), carbon nanotubes (CNTs) and a mixture of fillers GNP/CNT were prepared. The segregated structure of nanocarbon network in these composites leads to the excellent electromagnetic shielding (EMI SET), and an absorption-dominated shielding mechanism in the investigated range 26-37.5 GHz. The substitution of GNP particles by CNTs promotes the lowering of the percolation threshold and enhances EMI SET compared with composites (CMs) filled only GNPs. So, the composite with 6 vol.% (GNP/CNT) exhibited an EMI SET of 45.0 dB at the shield thickness of 1 mm.

Controlled Synthesis of Sulfur-Rich Polymeric Selenium Sulfides as Promising Electrode Materials for Long-Life, High-Rate Lithium Metal Batteries.

High-energy lithium/sulfur (Li/S) batteries still suffer from unsatisfactory cycle life and poor rate capability caused by the polysulfides shuttle and insulating nature of S cathodes. Here, we report our findings in the controlled synthesis of selenium (Se)-containing S-rich co-polymers of various compositions as novel cathode materials through a facile inverse vulcanization of S with selenium disulfide (SeS2) and 1,3-diisopropenylbenzene (DIB) as co-monomers. Nuclear magnetic resonance and X-ray photoelectron spectroscopy results show that divinyl functional groups of DIB were chemically cross-linked with S/SeS2 chain radicals through a ring-opening polymerization. The newly formed bonds of C-S, C-Se, and S-Se in novel S-SeS2-DIB co-polymers effectively alleviate the shuttle effects of polysulfides/polyselenides. Furthermore, various electrochemical techniques confirm the positive roles of Se-containing co-polymers in enhancing the electrode reaction kinetics and the formation of stable solid electrolyte interphase layer with low charge-transfer resistance, leading to improved high-rate performances. The as-synthesized co-polymer was then infiltrated into well-interconnected, porous nanocarbon networks (Ketjenblack EC600JD, KB600) to provide effective paths for the fast electron transport. Due to the synergistic combination of chemical and physical confinement of the reaction intermediates during cycling, good reversibility for 500 cycles with a low decay rate of 0.0549% per cycle was achieved at 1000 mA g-1. These encouraging results suggest that the combination of chemical incorporation of SeS2 into S-rich co-polymer and the physical confinement of carbon networks is a promising strategy for advancing Li/S batteries and their viability for practical applications.

Graphdiyne Containing Atomically Precise N Atoms for Efficient Anchoring of Lithium Ion

The qualitative and quantitative nitrogen-doping strategy for carbon materials is reported here. Novel porous nanocarbon networks pyrimidine-graphdiyne (PM-GDY) and pyridine-graphdiyne (PY-GDY) films with large areas were successfully prepared. These films are self-supported, uniform, continuous, flexible, transparent, and quantitively doped with merely pyridine-like nitrogen (N) atoms through the facile chemical synthesis route. Theoretical predictions imply these N doped carbonaceous materials are much favorable for storing lithium (Li)-ions since the pyridinic N can enhance the interrelated binding energy. As predicted, PY-GDY and PM-GDY display excellent electrochemical performance as anode materials of LIBs, such as the superior rate capability, the high capacity of 1168 (1165) mA h g-1 at current density of 100 mA g-1 for PY-GDY (PM-GDY), and the excellent stability of cycling for 1500 (4000) cycles at 5000 mA g-1 for PY-GDY (PM-GDY).

Facile fabrication of highly conductive polystyrene/nanocarbon composites with robust interconnected network via electrostatic attraction strategy

Highly conductive composites with an interconnected nanocarbon network were prepared via an electrostatic self-assembly and hot-pressing process.

Effect of the amount of nickel sulphide, molybdenum disulphide and carbon nanosupport on a Tafel slope and overpotential optimization

A Tafel slope of 40 mV dec−1 and a very small overpotential were measured for our NiSMoS2G nanocatalyst, prepared using a scalable approach, and consisting of NiS nanoparticles covered by a stabilizing coating of MoS2 nanosheets, on unsophisticated and easy to obtain physical exfoliated graphite. A careful study proves that it is possible to improve the Tafel slope and the overpotential through the optimization of amounts of the different components. The conductive nanocarbon network, the highly active to charge accumulation of NiS nanoparticles and the coupling with MoS2 nanosheets, exposing a large number of edges, result in a very high hydrogen production rate of 1.63 ml cm−2 h−1 at −0.12 V, measured by means of an on-line mass spectrometry analysis.

Tunable water sensitive polymeric composites with synergistic graphene and carbon nanotubes

Hybrid nano-carbons of the reduced graphene oxide (rGO) and carbon nanotubes (CNTs) were utilized to fabricate the electrically conductive polymeric composites which exhibited superior flexibility, conductivity and tunable sensitivity to water exposure. Besides the conduction, morphologies and microstructure of the nanocarbon networks, the static and dynamic wetting behaviors as well as the absorption properties of the hybrid nanocarbons and the polymer composites were investigated. The emphasis was put on the influence of the composition on the sensory properties. The synergistic rGO-CNTs were found to magnify the water sensing, which may attribute to the swelling effect on the CNTs entanglement segregated by the rGO sheets. The findings may greatly benefit the exploration of nanocarbons in the field of the flexible sensory materials.

3D carbon networks and their polymer composites: Fabrication and electromechanical investigations of neat Aerographite and Aerographite-based PNCs under compressive load

Aerographite is a lightweight 3D nanocarbon network which offers covalent interconnections for polymer nanocomposites (PNCs). Here, the electrical and mechanical properties of neat Aerographite and Aerographite-based PNCs are investigated in detail. The Aerographite filler networks consist of hollow, graphitic tubes of μm-sized diameters and nm-sized wall thicknesses. Different densities of Aerographite in the range of 0.6–13.9 mg/cm3 have been investigated towards their mechanical deformation behavior, electrical conductivities and piezoresistive response under compression. This basic characterization of filler networks is compared to resulting PNCs if the Aerographite is fully embedded in epoxy matrix. It can be shown that the use of 3D interconnected Aerographite results in high electrical conductivities at low filler contents, e.g., 2–8.7 S/m for weight fractions of 0.1–1.2 wt.-%. The neat Aerographite has been characterized in detail by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy techniques. To explain the observed piezoresistive behavior of these 3D nanocarbon-based PNCs, a qualitative micromechanical model is introduced. The model describes the internal graphitic wall slippage and loss of interconnections of the inner electrically conductive networks under load. The piezoresistive response of Aerographite-based PNCs can be directly correlated to the applied outer mechanical loads.

Hierarchical porous LiFePO4/Carbon composite electrodes for lithium-ion batteries

Hierarchical porous LiFePO4/C composite has been successfully synthesised via evaporative self-assembly induced by vegetable proteins. The morphologies and structures are investigated by X-ray diffractometer, scanning electron microscope and transmission electron microscope. Hierarchical porous LiFePO4/C composite presents the connected hierarchical porous structure and nano-carbon network embedded in connected hierarchical pores. LiFePO4/C composite with 5 wt% vegetable proteins (LFP-5C) delivers a higher capacity of 166.8 mA h g−1 than LiFePO4/C composite with 8 wt% vegetable protein (LFP-8C) (161.4 mA h g−1) at 0.1 C rate. However, at a high rate of 30 C, LFP-8C exhibits a little higher discharge capacity of 148.6 mA h g−1and capacity retention of 97.3% after 100 cycles than LFP-5C (145.6 mA h g−1, 96.8%). The hierarchical porous LiFePO4/C composite is a promising material for practical application in lithium-ion battery.

Biomass-Derived Electrode for Next Generation Lithium-Ion Capacitors.

We report the fabrication of a carbon-based high energy density Li-ion hybrid electrochemical capacitor (Li-HEC) from low cost and eco-friendly materials. High surface area (2448±20 m(2) g(-1) ) activated carbon (AC) is derived from the environmentally threatening plant, Prosopis juliflora, and used as the positive electrode in a Li-HEC assembly. Natural graphite is employed as negative electrode and electrochemically pre-lithiated prior to the Li-HEC fabrication. The Li-HEC delivers a specific energy of 162.3 Wh kg(-1) and exhibits excellent cyclability (i.e., ∼79 % of initial capacity is retained after 7000 cycles). The superior electrochemical performance of Li-HEC benefits from the tube-like unique structural features of the AC. Also, the presence of a graphitic nanocarbon network improves the ion transport, and the formed micro- and meso-porous network acts as reservoir for the accommodation of charge carriers.

Wet Chemistry Synthesis of Multidimensional Nanocarbon-Sulfur Hybrid Materials with Ultrahigh Sulfur Loading for Lithium-Sulfur Batteries.

An optimized nanocarbon-sulfur cathode material with ultrahigh sulfur loading of up to 90 wt % is realized in the form of sulfur nanolayer-coated three-dimensional (3D) conducting network. This 3D nanocarbon-sulfur network combines three different nanocarbons, as follows: zero-dimensional carbon nanoparticle, one-dimensional carbon nanotube, and two-dimensional graphene. This 3D nanocarbon-sulfur network is synthesized by using a method based on soluble chemistry of elemental sulfur and three types of nanocarbons in well-chosen solvents. The resultant sulfur-carbon material shows a high specific capacity of 1115 mA h g(-1) at 0.02C and good rate performance of 551 mA h g(-1) at 1C based on the mass of sulfur-carbon composite. Good battery performance can be attributed to the homogeneous compositing of sulfur with the 3D hierarchical hybrid nanocarbon networks at nanometer scale, which provides efficient multidimensional transport pathways for electrons and ions. Wet chemical method developed here provides an easy and cost-effective way to prepare sulfur-carbon cathode materials with high sulfur loading for application in high-energy Li-S batteries.

Preparation and electrochemical performance of LiFePO4/C microspheres by a facile and novel co-precipitation

LiFePO4 and LiFePO4/C microspheres are successfully synthesized via facile co-precipitation in an elevated temperature oil bath. Their morphologies and structures are investigated by X-ray diffractometer, scanning electron microscope and transmission electron microscope. LiFePO4/C microspheres are uniform between 2 and 4μm in diameter and composed of nanoparticles from 30 to 80nm in size. Nanoparticles are coated by a thin nano-carbon layer and imbedded into three-dimensional nano-carbon networks. LiFePO4/C microspheres exhibit a high tap density (1.82gcm−3), deliver large reversible discharge capacity of 165mAhg−1 at 0.1C rate, excellent rate capability of 106mAhg−1 at 50C rate, and capacity retention over 98% after 20 cycles even applied 50C rate. Therefore, the material is a potential candidate for high-power lithium ion batteries.

Joule Heating Characteristics of Emulsion‐Templated Graphene Aerogels

The Joule heating properties of an ultralight nanocarbon aerogel are investigated with a view to potential applications as energy‐efficient, local gas heater, and other systems. Thermally reduced graphene oxide (rGO) aerogels (10 mg cm−3) with defined shape are produced via emulsion‐templating. Relevant material properties, including thermal conductivity, electrical conductivity and porosity, are assessed. Repeatable Joule heating up to 200 °C at comparatively low voltages (≈1 V) and electrical power inputs (≈2.5 W cm−3) is demonstrated. The steady‐state core and surface temperatures are measured, analyzed and compared to analogous two‐dimensional nanocarbon film heaters. The assessment of temperature uniformity suggests that heat losses are dominated by conductive and convective heat dissipation at the temperature range studied. The radial temperature gradient of an uninsulated, Joule‐heated sample is analyzed to estimate the aerogel's thermal conductivity (around 0.4 W m−1 K−1). Fast initial Joule heating kinetics and cooling rates (up to 10 K s−1) are exploited for rapid and repeatable temperature cycling, important for potential applications as local gas heaters, in catalysis, and for regenerable of solid adsorbents. These principles may be relevant to wide range of nanocarbon networks and applications.

Construction of the nano-carbon connections among the carbon-coated LiFe0.8Mn0.2PO4 grains by sol-gel technique

Nano-carbon connections among carbon-coated LiFe0.8Mn0.2PO4 grains are successfully constructed using polyacrylic acid and sucrose as carbon sources by sol-gel method, which can improve the electrochemical performance of LiFe0.8Mn0.2PO4. Samples were characterised by X-ray diffraction, scanning electron microscopy and electrochemical tests. The electrochemical tests show LiFe0.8Mn0.2PO4 grains connected by nano-carbon networks obtain the discharge specific capacity of 165 mA h g−1 at 0.1 C rate and excellent rate capability. Its specific capacity reaches 122 mA h g−1 at 5 C rate. Its capacity retention at 5 C rate attains 97% cycled 100 cycles. Therefore the construction of nano-carbon networks offers an effective and convenient technique to improve the specific capacities and rate capabilities of electrode materials of low electronic conductivity.