Revisiting Lithium- and Sodium-Ion Storage in Hard Carbon Anodes

The galvanostatic lithiation/sodiation voltage profiles of hard carbon anodes are simple, with a sloping drop followed by a plateau. However, a precise understanding of the corresponding redox sites and storage mechanisms is still elusive, which hinders further development in commercial applications. Here, a comprehensive comparison of the lithium- and sodium-ion storage behaviors of hard carbon is conducted, yielding the following key findings: 1) the sloping voltage section is presented by the lithium-ion intercalation in the graphitic lattices of hard carbons, whereas it mainly arises from the chemisorption of sodium ions on their inner surfaces constituting closed pores, even if the graphitic lattices are unoccupied; 2) the redox sites for the plateau capacities are the same as those for the closed pores regardless of the alkali ions; 3) the sodiation plateau capacities are mostly determined by the volume of the available closed pore, whereas the lithiation plateau capacities are primarily affected by the intercalation propensity; and 4) the intercalation preference and the plateau capacity have an inverse correlation. These findings from extensive characterizations and theoretical investigations provide a relatively clear elucidation of the electrochemical footprint of hard carbon anodes in relation to the redox mechanisms and storage sites for lithium and sodium ions, thereby providing a more rational design strategy for constructing better hard carbon anodes.

Understanding the Effects of Interfacial Lithium Ion Concentration on Lithium Metal Anode

Despite the development of multidimensional state-of-the-art electrode materials for constructing better lithium metal anodes (LMAs), the key factors influencing the electrochemical performance of LMAs are still poorly understood. Herein, it is demonstrated that the local lithium ion concentration at the interface between the electrode and electrolyte exerts significant influence on the electrochemical performance of LMAs. The local ion concentration is multiplied by introducing pseudocapacitive nanocarbons (PNCs) containing numerous heteroatoms, because PNCs can store large numbers of lithium ions in a pseudocapacitive manner, and promote the formation of an electrochemical double layer. The high interfacial lithium ion concentration induces the formation of lithium-rich inorganic solid-electrolyte-interface layers with high ionic conductivities, and facilitates sustainable and stable supplies of lithium ion charge carriers on the overall active surfaces of the PNCs. Accordingly, the PNC-induced LMA exhibits high Coulombic efficiencies, high rate capabilities, and stable cycling performance.

A Biodegradable Secondary Battery and its Biodegradation Mechanism for Eco-Friendly Energy-Storage Systems

The production of rechargeable batteries is rapidly expanding, and there are going to be new challenges in the near future about how the potential environmental impact caused by the disposal of the large volume of the used batteries can be minimized. Herein, a novel strategy is proposed to address these concerns by applying biodegradable device technology. An eco-friendly and biodegradable sodium-ion secondary battery (SIB) is developed through extensive material screening followed by the synthesis of biodegradable electrodes and their seamless assembly with an unconventional biodegradable separator, electrolyte, and package. Each battery component decomposes in nature into non-toxic compounds or elements via hydrolysis and/or fungal degradation, with all of the biodegradation products naturally abundant and eco-friendly. Detailed biodegradation mechanisms and toxicity influence of each component on living organisms are determined. In addition, this new SIB delivers performance comparable to that of conventional non-degradable SIBs. The strategy and findings suggest a novel eco-friendly biodegradable paradigm for large-scale rechargeable battery systems.

Advances in the Design of 3D-Structured Electrode Materials for Lithium-Metal Anodes

Although the lithium-metal anode (LMA) can deliver a high theoretical capacity of ≈3860 mAh g^-1 at a low redox potential of -3.040 V (vs the standard hydrogen electrode), its application in rechargeable batteries is hindered by the poor Coulombic efficiency and safety issues caused by dendritic metal growth. Consequently, careful electrode design, electrolyte engineering, solid-electrolyte interface control, protective layer introduction, and other strategies are suggested as possible solutions. In particular, one should note the great potential of 3D-structured electrode materials, which feature high active specific surface areas and stereoscopic structures with multitudinous lithiophilic sites and can therefore facilitate rapid Li-ion flux and metal nucleation as well as mitigate Li dendrite formation through the kinetic control of metal deposition even at high local current densities. This progress report reviews the design of 3D-structured electrode materials for LMA according to their categories, namely 1) metal-based materials, 2) carbon-based materials, and 3) their hybrids, and allows the results obtained under different experimental conditions to be seen at a single glance, thus being helpful for researchers working in related fields.

Hierarchically Nanoporous 3D Assembly Composed of Functionalized Onion-Like Graphitic Carbon Nanospheres for Anode-Minimized Li Metal Batteries

Despite the recent attention for Li metal anode (LMA) with high theoretical specific capacity of ≈3860 mA h g^-1 , it suffers from not enough practical energy densities and safety concerns originating from the excessive metal load, which is essential to compensate for the loss of Li sources resulting from their poor coulombic efficiencies (CEs). Therefore, the development of high-performance LMA is needed to realize anode-minimized Li metal batteries (LMBs). In this study, high-performance LMAs are produced by introducing a hierarchically nanoporous assembly (HNA) composed of functionalized onion-like graphitic carbon building blocks, several nanometers in diameter, as a catalytic scaffold for Li-metal storage. The HNA-based electrodes lead to a high Li ion concentration in the nanoporous structure, showing a high CE of ≈99.1%, high rate capability of 12 mA cm^-2 , and a stable cycling behavior of more than 750 cycles. In addition, anode-minimized LMBs are achieved using a HNA that has limited Li content (≈0.13 mg cm^-2 ), corresponding to 6.5% of the cathode material (commercial NCM622 (≈2 mg cm^-2 )). The LMBs demonstrate a feasible electrochemical performance with high energy and power densities of ≈510 Wh kg_electrode ^-1 and ≈2760 W kg_electrode ^-1 , respectively, for more than 100 cycles.

Electrolyte-Dependent Sodium Ion Transport Behaviors in Hard Carbon Anode

A comprehensive study is conducted on hard carbon (HC) series samples by tuning the graphitic local microstructures systematically as an anode for SIBs in both carbonate- (CBE) and glyme-based electrolytes (GBE). The results reveal more detailed charge storage characters of HCs on the LVP section. 1) The LVP capacity is closely related to the prismatic surface area to the basal plane as well as the bulk density, regardless of electrolyte systems. 2) The glyme-sodium ion complex can facilitate sodium ion delivery into the internal closed pores of the HCs along with not well-ordered graphitic structures. 3) The glyme-mediated sodium ion-storage behavior causes significant decreases in both surface film resistance and charge transfer resistance, leading to enhanced rate capability. 4) The LVP originates from the formation of pseudo-metallic sodium nanoclusters, which are the same in a CBE and GBE. These results provide insight into the sodium ion-storage behaviors of HCs, particularly on the interrelationship between graphitic local microstructures and electrolyte systems. In addition, a high-performance HC anode with a plateau capacity of ≈300 mA h g^-1 is designed based on the information, and its workability is demonstrated in a full-cell SIB device.

Stable and High-Power Calcium-Ion Batteries Enabled by Calcium Intercalation into Graphite

Calcium-ion batteries (CIBs) are considered to be promising next-generation energy storage systems because of the natural abundance of calcium and the multivalent calcium ions with low redox potential close to that of lithium. However, the practical realization of high-energy and high-power CIBs is elusive owing to the lack of suitable electrodes and the sluggish diffusion of calcium ions in most intercalation hosts. Herein, it is demonstrated that calcium-ion intercalation can be remarkably fast and reversible in natural graphite, constituting the first step toward the realization of high-power calcium electrodes. It is shown that a graphite electrode exhibits an exceptionally high rate capability up to 2 A g^-1 , delivering ≈75% of the specific capacity at 50 mA g^-1 with full calcium intercalation in graphite corresponding to ≈97 mAh g^-1 . Moreover, the capacity stably maintains over 200 cycles without notable cycle degradation. It is found that the calcium ions are intercalated into graphite galleries with a staging process. The intercalation mechanisms of the "calciated" graphite are elucidated using a suite of techniques including synchrotron in situ X-ray diffraction, nuclear magnetic resonance, and first-principles calculations. The versatile intercalation chemistry of graphite observed here is expected to spur the development of high-power CIBs.

Magnesiophilic Graphitic Carbon Nanosubstrate for Highly Efficient and Fast-Rechargeable Mg Metal Batteries

The high volumetric energy density of rechargeable Mg batteries (RMBs) gives them a competitive advantage over current Li ion batteries, which originates from the high volumetric capacity (∼3833 mA h cm^-3) of bivalent Mg metal anodes (MMAs). On the other hand, despite their importance, there are few reports on research strategies to improve the electrochemical performance of MMAs. This paper reports that catalytic carbon nanosubstrates rather than metal-based substrates, such as Mo, Cu, and stainless steel, are essential in MMAs to improve the electrochemical performance of RMBs. In particular, three-dimensional macroporous graphitic carbon nanosubstrates (GC-NSs) with high electrical conductivities can accommodate Mg metal with significantly higher rate capabilities and Coulombic efficiencies than metal substrates, resulting in a more stable and longer-term cycling performance over 1000 cycles. In addition, while metal-based substrates suffered from undesirable Mg peeling-off, homogeneous Mg metal deposition is well-guided in GC-NSs owing to the better affinity of the Mg²⁺ ion. These results are supported by density functional theory calculations and ex-situ characterization.

Anode-Free Sodium Metal Batteries Based on Nanohybrid Core-Shell Templates

Anode-free sodium metal batteries (AF-SMBs) can deliver high energy and enormous power, but their cycle lives are still insufficient for them to be practical as a power source in modern electronic devices and/or grid systems. In this study, a nanohybrid template based on high aspect-ratio silver nanofibers and nitrogen-rich carbon thin layers as a core-shell structure is designed to improve the Coulombic efficiency (CE) and cycling performance of AF-SMBs. The catalytic nanohybrid templates dramatically reduce the voltage overshooting caused by metal nucleation to one-fifth that of a bare Al foil electrode (≈6 mV vs ≈30 mV), and high average CE values of >99% are achieved over a wide range of current rates from 0.2 to 8 mA cm^-2 . Moreover, exceptionally long cycle lives for more than 1600 cycles and an additional 1500 cycles are achieved with a highly stable CE of >99.9%. These results show that AF-SMBs are feasible with the nanohybrid electrode system.

Intensification of Pseudocapacitance by Nanopore Engineering on Waste-Bamboo-Derived Carbon as a Positive Electrode for Lithium-Ion Batteries

Nanoporous carbon, including redox-active functional groups, can be a promising active electrode material (AEM) as a positive electrode for lithium-ion batteries owing to its high electrochemical performance originating from the host-free surface-driven charge storage process. This study examined the effects of the nanopore size on the pseudocapacitance of the nanoporous carbon materials using nanopore-engineered carbon-based AEMs (NE-C-AEMs). The pseudocapacitance of NE-C-AEMs was intensified, when the pore diameter was ≥2 nm in a voltage range of 1.0~4.8 V vs Li⁺/Li under the conventional carbonate-based electrolyte system, showing a high specific capacity of ~485 mA·h·g⁻¹. In addition, the NE-C-AEMs exhibited high rate capabilities at current ranges from 0.2 to 4.0 A·g⁻¹ as well as stable cycling behavior for more than 300 cycles. The high electrochemical performance of NE-C-AEMs was demonstrated by full-cell tests with a graphite nanosheet anode, where a high specific energy and power of ~345 Wh·kg⁻¹ and ~6100 W·Kg⁻¹, respectively, were achieved.

Catalytic Pyroprotein Seed Layers for Sodium Metal Anodes

We report a pyroprotein seed layer (PSL, ∼100 nm in thickness)-coated Cu foil electrode (PSL-Cu) demonstrating highly reversible Na metal storage behavior with a mean Coulombic efficiency (CE) of ∼99.96% over 300 cycles in a glyme-based electrolyte. Via a synergistic effect with the electrolyte, the carbonaceous thin film containing numerous nucleophilic active sites guides the homogeneous Na metal deposition/stripping process with the formation of numerous catalytic seeds, resulting in remarkably stable cycling and a low Na metal nucleation overpotential of ∼10 mV. In addition, the CE deviation values of the PSL-Cu electrode were ∼0.43% in several cell tests, demonstrating its reliable cycling behavior with low cell-to-cell variation. The practicality of PSL-Cu was further demonstrated via full-cell experiments with a polyanion cathode, in which it achieved a high specific power density and energy density of 3,800 W kg^-1 and ∼402 W h kg^-1, respectively. This work provides a simple process for the fabrication of a Na metal anode.

Pyrolytic Carbon Nanosheets for Ultrafast and Ultrastable Sodium-Ion Storage

Na-ion cointercalation in the graphite host structure in a glyme-based electrolyte represents a new possibility for using carbon-based materials (CMs) as anodes for Na-ion storage. However, local microstructures and nanoscale morphological features in CMs affect their electrochemical performances; they require intensive studies to achieve high levels of Na-ion storage performances. Here, pyrolytic carbon nanosheets (PCNs) composed of multitudinous graphitic nanocrystals are prepared from renewable bioresources by heating. In particular, PCN-2800 prepared by heating at 2800 °C has a distinctive sp² carbon bonding nature, crystalline domain size of ≈44.2 Å, and high electrical conductivity of ≈320 S cm^-1 , presenting significantly high rate capability at 600 C (60 A g^-1 ) and stable cycling behaviors over 40 000 cycles as an anode for Na-ion storage. The results of this study show the unusual graphitization behaviors of a char-type carbon precursor and exceptionally high rate and cycling performances of the resulting graphitic material, PCN-2800, even surpassing those of supercapacitors.

Hierarchically Macroporous Graphitic Nanowebs Exhibiting Ultra-fast and Stable Charge Storage Performance

The macro/microstructures of carbon-based electrode materials for supercapacitor applications play a key role in their electrochemical performance. In this study, hierarchically macroporous graphitic nanowebs (HM-GNWs) were prepared from bacterial cellulose by high-temperature heating at 2400 °C. The HM-GNWs were composed of well-developed graphitic nanobuilding blocks with a high aspect ratio, which was entangled as a nanoweb structure. The morphological and microstructural characteristics of the HM-GNWs resulted in remarkable charge storage performance. In particular, the HM-GNWs exhibited very fast charge storage behaviors at scan rates ranging from 5 to 100 V s-1, in which area capacitances ranging from ~ 8.9 to 3.8 mF cm-2 were achieved. In addition, ~ 97% capacitance retention was observed after long-term cycling for more than 1,000,000 cycles.

Nanoconfinement effects of chemically reduced graphene oxide nanoribbons on poly(vinyl chloride)

Polymeric nanocomposites with graphene-based nanocarbons (GNCs) have been extensively studied with emphasis on the percolation of nanofillers toward electrical, rheological, and mechanical reinforcement. In this study, we report an unusual indirect reinforcing phenomenon of highly defective GNCs dispersed in the poly(vinyl chloride) (PVC) matrix via densification of the polymer packing originating from nanoscale confinement. Herein, chemically reduced graphene oxide nanoribbons (C-rGONRs) are employed as a nanofiller. The inclusion of defective and oxygen-functionalized C-rGONRs resulted in a dramatic densification of the PVC host with extremely low C-rGONR loading, largely exceeding the theoretical calculation from a rule of mixture. Along with the densification, the glass transition temperature of PVC also increased by 28.6 °C at 0.1 wt% filler loading. Remarkably, the oxygen barrier property and mechanical toughness under tension for the PVC/C-rGONR nanocomposite were the maximum when the greatest densification occurred. The structure-property relationship of the nanocomposites has been discussed with an emphasis on the nanoscale confinement phenomenon.

Tin Sulfide-Based Nanohybrid for High-Performance Anode of Sodium-Ion Batteries

Nanohybrid anode materials for Na-ion batteries (NIBs) based on conversion and/or alloying reactions can provide significantly improved energy and power characteristics, while suffering from low Coulombic efficiency and unfavorable voltage properties. An NIB paper-type nanohybrid anode (PNA) based on tin sulfide nanoparticles and acid-treated multiwalled carbon nanotubes is reported. In 1 m NaPF₆ dissolved in diethylene glycol dimethyl ether as an electrolyte, the above PNA shows a high reversible capacity of ≈1200 mAh g^-1 and a large voltage plateau corresponding to a capacity of ≈550 mAh g^-1 in the low-voltage region of ≈0.1 V versus Na⁺ /Na, exhibiting high rate capabilities at a current rate of 1 A g^-1 and good cycling performance over 250 cycles. In addition, the PNA exhibits a high first Coulombic efficiency of ≈90%, achieving values above 99% during subsequent cycles. Furthermore, the feasibility of PNA usage is demonstrated by full-cell tests with a reported cathode, which results in high specific energy and power values of ≈256 Wh kg^-1 and 471 W kg^-1 , respectively, with stable cycling.

Ultra strong pyroprotein fibres with long-range ordering

Silks are protein-based natural structured materials with an unusual combination of high strength and elongation. Their unique microstructural features composed of hard β-sheet crystals aligned within a soft amorphous region lead to the robust properties of silks. Herein we report a large enhancement in the intrinsic properties of silk through the transformation of the basic building blocks into a poly-hexagonal carbon structure by a simple heat treatment with axial stretching. The carbon clusters originating from the β-sheet retain the preferred orientation along the fibre axis, resulting in a long-range-ordered graphitic structure by increasing heat-treatment temperatures and leading improvements in mechanical properties with a maximum strength and modulus up to ∼2.6 and ∼470 GPa, respectively, almost four and thirty times surpassing those of raw silk. Moreover, the formation of sp 2 carbon configurations induce a significant change in the electrical properties (e.g. an electrical conductivity up to 4.37 × 103 S cm-1).The mechanical properties of silk are determined by tight stacks of sheet-like peptide crystals distributed in amorphous regions. Here, the authors heat and stretch silk fibres to align these crystal into a long range ordered carbon structure and dramatically enhance the silk strength.

Pyroprotein-Based Electronic Textiles with High Stability

Thermally reducible pyroprotein-based electronic textiles (e-textiles) are fabricated using graphene oxide and a pyroprotein such as cocoon silk and spider web without any chemical agents. The electrical conductivity of the e-textile is 11.63 S cm^-1 , which is maintained even in bending, washing, and temperature variation.

Long-Lasting Nb2O5-Based Nanocomposite Materials for Li-Ion Storage

Advanced nanostructured hybrid materials can help us overcome the electrochemical performance limitations of current energy storage devices. In this study, three-dimensional porous carbon nanowebs (3D-CNWs) with numerous included orthorhombic Nb₂O₅ (T-Nb₂O₅) nanoparticles were fabricated using a microbe-derived nanostructure. The 3D-CNW/T-Nb₂O₅ nanocomposites showed an exceptionally stable long-term cycling performance over 70 000 cycles, a high reversible capacity of ∼125 mA h g^-1, and fast Li-ion storage kinetics in a coin-type two-electrode system using Li metal. In addition, energy storage devices based on the above nanocomposites achieved a high specific energy of ∼80 W h kg^-1 together with a high specific power of ∼5300 W kg^-1 and outstanding cycling performance with ∼80% capacitance retention after 35 000 cycles.

Synergistic catalytic effects of oxygen and nitrogen functional groups on active carbon electrodes for all-vanadium redox flow batteries

Thin pyroprotein coating layers containing numerous oxygen and nitrogen heteroatoms were introduced on the surface of CFs (P-CFs), and their catalytic effects on the redox reaction of V²⁺/V³⁺ couples for VRFBs were investigated.

Chemoprotective and Adjuvant Effects of Immunomodulator Ginsan in Cyclophosphamide-Treated Normal and Tumor Bearing Mice

Ginsan is a polysaccharide extracted from Panax ginseng that is known to have multiple immunomodulatory effects. This study evaluates the chemoprotective effect of ginsan on normal mice and the adjuvant effect on tumor bearing mice in combination with cyclophosphamide (CP). Ginsan (100 mg/kg) was injected 24 h before or after a sublethal dose of a CP treatment. The mice pre-treated with ginsan all died within 10 days whereas up to 53% of the mice post-treated with ginsan increased survival to day 30 compared with only 10% in the CP alone treated group on day 30. The post-treatment of ginsan accelerated the recovery of the bone marrow cells and blood neutrophils by approximately 1.3- and 1.75-fold compared to CP treated control mice at 5 days after CP administration, respectively. These marked differences in activity between the pre- and post-treatment of ginsan with CP was clarified by examining the mRNA expression levels of several cytokines in spleen cells and the self-renewal potential of hematopoietic progenitor cells, CFU-s. The post-treatment with ginsan increased the mRNA expression levels of TNF-α, IL-1β, IL-6, SCF, and GM-CSF with respect to that of the CP alone or ginsan pre-treated group. Similarly, the number of CFU-s was significantly higher in the mice post-treated with ginsan. The inhibition of tumor growth and survival elongation was also observed when ginsan was administered 24 h after the CP treatment. These results show that the post-treatment with ginsan had an immunomodulating and adjuvant effect in combination with CP, which indicates its wide applications in reducing the adverse effects of chemotherapy and improving the general conditions of patients.

Citrus-Peel-Derived, Nanoporous Carbon Nanosheets Containing Redox-Active Heteroatoms for Sodium-Ion Storage

Advanced design of nanostructured functional carbon materials for use in sustainable energy storage systems suffers from complex fabrication procedures and the use of special methods and/or expensive precursors, limiting their practical applications. In this study, nanoporous carbon nanosheets (NP-CNSs) containing numerous redox-active heteroatoms (C/O and C/N ratios of 5.5 and 34.3, respectively) were fabricated from citrus peels by simply heating the peels in the presence of potassium ions. The NP-CNSs had a 2D-like morphology with a high aspect ratio of >100, high specific surface area of 1167 m(2) g(-1), and a large amount of nanopores between 1 and 5 nm. The NP-CNSs also had an electrical conductivity of 2.6 × 10(1) s cm(-1), which is approximately 50 times higher than that of reduced graphene oxide. These unique material properties resulted in superior electrochemical performance with a high specific capacity of 140 mAh g(-1) in the cathodic potential range. In addition, symmetric full-cell devices based on the NP-CNSs showed excellent cyclic performance over 100,000 repetitive cycles.

Dispersion stability of chemically reduced graphene oxide nanoribbons in organic solvents

In this study, the dispersion stability of graphene oxide nanoribbons (GONRs) and chemically reduced GONRs (CR-GONRs) in various organic solvents was investigated.

Sodium-Ion Storage in Pyroprotein-Based Carbon Nanoplates

Pyroprotein-based carbon nanoplates are fabricated from self-assembled silk proteins as a versatile platform to examine sodium-ion storage characteristics in various carbon environments. It is found that, depending on the local carbon structure, sodium ions are stored via chemi-/physisorption, insertion, or nanoclustering of metallic sodium.

Microporous carbon nanosheets with redox-active heteroatoms for pseudocapacitive charge storage

We report microporous carbon nanosheets containing numerous redox active heteroatoms fabricated from exfoliated waste coffee grounds by simple heating with KOH for pseudocapacitive charge storage. We found that various heteroatom combinations in carbonaceous materials can be a redox host for lithium ion storage. The bio-inspired nanomaterials had unique characteristics, showing superior electrochemical performances as cathode for asymmetric pseudocapacitors.

Carbonization of a stable β-sheet-rich silk protein into a pseudographitic pyroprotein

Silk proteins are of great interest to the scientific community owing to their unique mechanical properties and interesting biological functionality. In addition, the silk proteins are not burned out following heating, rather they are transformed into a carbonaceous solid, pyroprotein; several studies have identified potential carbon precursors for state-of-the-art technologies. However, no mechanism for the carbonization of proteins has yet been reported. Here we examine the structural and chemical changes of silk proteins systematically at temperatures above the onset of thermal degradation. We find that the β-sheet structure is transformed into an sp(2)-hybridized carbon hexagonal structure by simple heating to 350 °C. The pseudographitic crystalline layers grew to form highly ordered graphitic structures following further heating to 2,800 °C. Our results provide a mechanism for the thermal transition of the protein and demonstrate a potential strategy for designing pyroproteins using a clean system with a catalyst-free aqueous wet process for in vivo applications.

Hierarchically porous carbon nanosheets from waste coffee grounds for supercapacitors

The nanostructure design of porous carbon-based electrode materials is key to improving the electrochemical performance of supercapacitors. In this study, hierarchically porous carbon nanosheets (HP-CNSs) were fabricated using waste coffee grounds by in situ carbonization and activation processes using KOH. Despite the simple synthesis process, the HP-CNSs had a high aspect ratio nanostructure (∼20 nm thickness to several micrometers in lateral size), a high specific surface area of 1945.7 m(2) g(-1), numerous heteroatoms, and good electrical transport properties, as well as hierarchically porous characteristics (0.5-10 nm in size). HP-CNS-based supercapacitors showed a specific energy of 35.4 Wh kg(-1) at 11250 W kg(-1) and of 23 Wh kg(-1) for a 3 s charge/discharge current rate corresponding to a specific power of 30000 W kg(-1). Additionally, the HP-CNS supercapacitors demonstrated good cyclic performance over 5000 cycles.

Hierarchical porous carbon/MnO2 hybrids as supercapacitor electrodes

Hybrid electrodes of hierarchical porous carbon (HPC) and manganese oxide (MnO2) were synthesized using a fast surface redox reaction of potassium permanganate under facile immersion methods. The HPC/MnO2 hybrids had a number of micropores and macropores and the MnO2 nanoparticles acted as a pseudocapacitive material. The synergistic effects of electric double-layer capacitor (EDLC)-induced capacitance and pseudocapacitance brought about a better electrochemical performance of the HPC/MnO2 hybrid electrodes compared to that obtained with a single component. The hybrids showed a specific capacitance of 228 F g(-1) and good cycle stability over 1000 cycles.

Hierarchically porous carbon/polyaniline hybrid for use in supercapacitors

A hierarchically porous carbon (HPC)/polyaniline (PANI) hybrid electrode was prepared by the polymerization of PANI on the surface of the HPC via rapid-mixing polymerization. The surface morphologies and chemical composition of the HPC/PANI hybrid electrode were characterized using transmission electron microscopy and X-ray photoelectron spectroscopy (XPS), respectively. The surface morphologies and XPS results for the HPC, PANI and HPC/PANI hybrids indicate that PANI is coated on the surface of HPC in the HPC/PANI hybrids which have two different nitrogen groups as a benzenoid amine (-NH-) peak and positively charged nitrogen (N+) peak. The electrochemical performances of the HPC/PANI hybrids were analyzed by performing cyclic voltammetry and galvanostatic charge-discharge tests. The HPC/PANI hybrids showed a better specific capacitance (222 F/g) than HPC (111 F/g) because of effect of pseudocapacitor behavior. In addition, good cycle stabilities were maintained over 1000 cycles.

Nylon 610/graphene oxide composites prepared by in-situ interfacial polymerization

Nylon 610/nylon 610-grafted graphene oxide (nylon 610/GO-g-nylon 610) composites were fabricated using acyl chloride-functionalized graphene oxide by in-situ interfacial polymerization. GO-g-nylon 610 was synthesized by the condensation reaction between the acyl chloride groups of GO and the amino groups at the nylon 610 chains during the in-situ polymerization. Nylon 610/GO composites without grafting nylon 610 onto GO were also prepared to investigate the influence of grafting nylon 610 on the interfacial adhesion between GO and the nylon 610 matrix. The thermal properties of the nylon 610/GO-g-nylon 610 composites were enhanced with increasing GO-g-nylon 610 content in the nylon 610 matrix. The degradation temperature and thermal conductivity of the nylon 610/GO-g-nylon 610-10 composite were increased to 72.2 °C and 36.9%, respectively, compared with those of pure nylon 610. The crystallinity of the nylon 610/GO-g-nylon 610-10 composite was significantly lower than that of pure nylon 610 due to the hindered mobility of the nylon 610 chains by the strong interfacial adhesion between the GO-g-nylon 610 and the nylon 610 matrix.

Free-standing graphene-based nanohybrid paper electrode as an anode for lithium-ion batteries

Free-standing paper electrodes based on nitrogen-doped graphenes with mesoporous Mn₃O₄ nanoparticles were used as an anode for Li-ion batteries.

Free-standing nitrogen-doped reduced graphene oxide anode for lithium-ion batteries

Graphenes have been considered suitable candidate materials for electrodes of energy storage devices such as lithium-ion batteries (LIBs) because of their outstanding mechanical, thermal and electrical properties. However, there are problems when using these carbon materials for electrodes because of their low electrochemical performance. In this work, to improve the electrochemical performances of graphenes, free-standing nitrogen-doped reduced graphene oxides (FNRGOs) were prepared as an anode for LIBs using a facile vacuum filtration method and thermal annealing at different temperatures. X-ray diffraction and X-ray photoelectron spectroscopy were employed to characterize the prepared samples, and then their electrochemical performance was investigated by galvanostatic charge/discharge (GCD) tests. GCD tests revealed that FNRGO prepared from thermal annealing at 500 degrees C exhibited good initial reversible capacity (502 mA h/g at 50 mA/g (0.14 C)) and enhanced cycle stability (capacity retention of 90.5% after 50th cycles at 100 mA/g (0.27 C), which demonstrated that FNRGOs were suitable candidates as anodes for LIBs.

Silver nanowire catalysts on carbon nanotubes-incorporated bacterial cellulose membrane electrodes for oxygen reduction reaction

Silver nanowires have unique electrical, thermal and optical properties, which support their potential application in numerous fields including catalysis, electronics, optoelectronics, sensing, and surface-enhanced spectroscopy. Especially, their application such as catalysts for alkaline fuel cells (AFCs) have attracted much interest because of their superior electrical conductivity over that of any metal and their lower cost compared to Pt. In this study, multiwalled carbon nanotubes (MWCNTs)-incorporated bacterial cellulose (BC) membrane electrode with silver nanowire catalyst was prepared. First, acid-treated MWCNTs were incorporated into BC membranes and then freeze-dried after solvent exchange to tert-butanol in order to maintain the 3D-network macroporous structure. Second, silver nanowires synthesized by polyol process were introduced onto the surface of the MWCNTs-incorporated BC membrane through easy vacuum filtration. Finally, thermal treatment was carried out to confirm the effect of the PVP on the silver nanowire catalysts toward oxygen reduction reaction. The electrode with thermally treated silver nanowire had great electrocatalytic activity compared with non-treated one. These results suggest that the MWCNTs-incorporated BC electrode with silver nanowire catalysts after thermal treatment could be potentially used in cathodes of AFCs.

Synergistic effects of alkylated graphene oxide on the properties of polypropylene-based carbon nanocomposites

Polypropylene (PP)/carbon black (CB)-alkylated graphene oxide (AGO) hybrid nanocomposites were prepared via solution process and the synergistic effects of AGO on the properties of the PP/CB nanocomposites were investigated. AGO at a content of only 0.2 wt% formed an overlapped network structure in the PP matrix and affected the electrical, thermal and mechanical properties of the PP/CB nanocomposites. Specifically, PP/CB (5 wt%)-AGO (0.2 wt%) nanocomposites exhibited an electrical percolation threshold at lower CB contents than the PP/CB nanocomposites did, and the sheet resistance was decreased to 2.3 x 10(7) omega/sq. The thermal degradation temperature and recrystallization temperature of the PP/CB (10 wt%) nanocomposites were increased by 11.3 and 1.6 degrees C, respectively, by the addition of 0.2 wt% AGO. In addition, the Young's modulus of the PP/CB (10 wt%) nanocomposite was increased from 438.1 to 540.1 MPa.

Microporous carbon nanoplates from regenerated silk proteins for supercapacitors

Novel carbon-based microporous nanoplates containing numerous heteroatoms (H-CMNs) are fabricated from regenerated silk fibroin by the carbonization and activation of KOH. The H-CMNs exhibit superior electrochemical performance, displaying a specific capacitance of 264 F/g in aqueous electrolytes, a specific energy of 133 Wh/kg, a specific power of 217 kW/kg, and a stable cycle life over 10000 cycles.