One-pot hydrothermal synthesis and supercapacitive performance of nitrogen and MnO co-doped hierarchical porous carbon monoliths

Nitrogen and MnO co-doped hierarchical porous carbon monolith (N-MnO-HPCM) materials were synthesized through a facile one-pot hydrothermal method. The resulting N-MnO-HPCM materials had hierarchical porous structure, high BET surface area (606 m²/g), large pore volume (0.33 cm³/g), and contained evenly dispersed MnO nanoparticles of about 6 nm in the carbon matrix. Their electrochemical performances as electrodes for supercapacitors were investigated. N-MnO-HPCM material exhibited an excellent electrochemical performance with a specific capacitance of 261.7 F/g at a current density of 1 A/g. It also showed a good rate capability with 74% capacity retention at high current density (5 A/g), indicating its potential applications in supercapacitors.     

Transition metal loaded silicon carbide-derived carbons with enhanced catalytic properties

Carbide-derived carbons (CDC) with incorporated transition metal nanoparticles (～2.5 nm) were prepared using a microemulsion approach. Time-consuming post synthesis functionalization of the carbon support material can thus be avoided and nanoparticle sizes can be controlled by changing the microemulsion composition. This synthesis strategy is a technique for the preparation of highly porous carbon materials with a catalytically active component. In particular we investigated the integration of ruthenium, palladium, and platinum in a concentration ranging from 4.45 to 12 wt.%. It was found that the transition metal has a considerable influence on sorption properties of resulting nanoparticle-CDC composite materials. Depending on the used metal salt additive the surface area and the pore volume ranges from 1480 m²/g and 1.25 cm³/g for Pt to 2480 m²/g and 2.0 cm³/g for Ru doped carbons. Moreover, members of this material class show impressive properties as heterogeneous catalysts. The liquid phase oxidation of tetralin and the partial oxidation of methane were studied, and electrochemical applications were also investigated. Primarily Pt doped CDCs are highly active in the oxygen reduction reaction, which is of great importance in present day fuel cell research.     

Tailoring the surface chemistry and porosity of activated carbons: Evidence of reorganization and mobility of oxygenated surface groups

An activated carbon with developed porosity and surface area (S_BET = 2387 m² g⁻¹) was prepared by chemical activation and then oxidized with ammonium peroxydisulfate. The oxidation treatment destroyed mesopore walls leading to a severe surface area reduction. Specific thermal treatments were carried out in different portions of the oxidized sample to selectively remove the oxygenated surface complexes. The combination of different techniques revealed that thermal treatment between 300 and 500 °C produces a strong reorganization of oxygenated groups on the chemical structure of carbons. CO₂-evolving groups (around 75 wt.%) are selectively transformed into CO-evolving groups. These processes only occur inside the pores, and involve CO₂ desorption and re-adsorption in this temperature range. At a higher treatment temperature (700 °C), re-oxidation is prevented and the surface chemistry becomes quite similar to the original activated carbon.     

Relationship among the physicochemical properties,electrocatalytic performance and kinetics of carbon supported Pt catalyst for ethanol oxidation

A new carbon supported Pt (Pt/C(b)) catalyst was prepared by reducing H₂PtCl₆ in glycol solution using formic acid as a reducing agent, and has been found in this work to be highly active and stable for the electrochemical oxidation of ethanol. The preparation produces highly dispersed Pt particles, of 2.6 nm average size, and with high electrochemical surface area, 98 m²/g. The apparent activation energy of ethanol oxidation over the Pt/C(b) catalyst electrode is low, 10–14 kJ/mol, over the range of potentials from 0.3 to 0.6 V.     

Exceptional electrochemical performance of nitrogen-doped porous carbon for lithium storage

Crumpled nitrogen-doped porous carbon sheets are successfully fabricated via chemical activation of polypyrrole-functionalized graphene sheets with KOH (APGs). The obtained APGs with nitrogen doping, high surface area, porous and crumpled structure exhibit exceptional electrochemical performances as the electrode material for LIBs, including a superhigh reversible specific capacity of 1516.2 mAh g⁻¹, excellent cycling stability over 10,000 cycles, and good rate capability (133.2 mAh g⁻¹ even at a very high current density of 40 A g⁻¹). The chemical activation synthesis strategy might open new avenues for the design of high-performance carbon-based anode materials.     

Carbon–carbon asymmetric aqueous capacitor by pseudocapacitive positive and stable negative electrodes

An asymmetric aqueous capacitor was constructed by employing zeolite-templated carbon (ZTC) as a pseudocapacitive positive electrode and KOH-activated carbon as a stable negative electrode. The asymmetric capacitor can be operated with the working voltage of 1.4 V, and exhibits an energy density that is comparable to those of conventional capacitors utilizing organic electrolytes, thanks to the large pseudocapacitance of ZTC. Despite relatively thick electrode (0.2 mm) configuration, the asymmetric capacitor could be well operated under a current density of 500 mA g⁻¹.     

Chemical oxidation of residual carbon from ZnAl2O4 powders prepared by combustion synthesis

The removal of carbon residue from ZnAl₂O₄ nanopowders by annealing at 500–800 °C leads to a decrease of specific surface area from 228.1 m²/g to 47.6 m²/g. At the same time, the average crystallite size increased from 5.1 nm to 14.9 nm. In order to overcome these drawbacks, a new solution for removing the carbon residue has been suggested: chemical oxidation using hydrogen peroxide. In terms of carbon removal, a H₂O₂ treatment for 8 h at 107 °C proved to be equivalent to a heat treatment of 1 h at 600 °C. The benefits of chemical oxidation over thermal oxidation were obvious. The specific surface area was much larger (188.1 m²/g) in the case of the powder treated with H₂O₂. The average crystallite size (5.8 nm) of ZnAl₂O₄ powder treated with H₂O₂ was smaller than the crystallite size (8.2 nm) of the ZnAl₂O₄ powder annealed at 600 °C.     

Dense carbon monoliths for supercapacitors with outstanding volumetric capacitances

A commercially available dense carbon monolith (CM) and four carbon monoliths obtained from it have been studied as electrochemical capacitor electrodes in a two-electrode cell. CM has: (i) very high density (1.17 g cm⁻³), (ii) high electrical conductivity (9.3 S cm⁻¹), (iii) well-compacted and interconnected carbon spheres, (iv) homogeneous microporous structure and (v) apparent BET surface area of 957 m²g⁻¹. It presents interesting electrochemical behaviors (e.g., excellent gravimetric capacitance and outstanding volumetric capacitance). The textural characteristics of CM (porosity and surface chemistry) have been modified by means of different treatments. The electrochemical performances of the starting and treated monoliths have been analyzed as a function of their porous textures and surface chemistry, both on gravimetric and volumetric basis. The monoliths present high specific and volumetric capacitances (292 F g⁻¹ and 342 F cm⁻³), high energy densities (38 Wh kg⁻¹ and 44 Wh L⁻¹), and high power densities (176 W kg⁻¹ and 183 W L⁻¹). The specific and volumetric capacitances, especially the volumetric capacitance, are the highest ever reported for carbon monoliths. The high values are achieved due to a suitable combination of density, electrical conductivity, porosity and oxygen surface content.     

High rate performance activated carbons prepared from ginkgo shells for electrochemical supercapacitors

Partially graphitized ginkgo-based activated carbon (GGAC) is fabricated from ginkgo shells by pyrolysis, KOH activation and heat treatment using cobalt nitrate as graphitization catalyst. The graphitization temperature is 900 °C. The GGAC has a microporous structure and its specific surface area is 1775 m² g⁻¹. XRD patterns show that the carbon becomes more graphitic after heat treatment. The specific capacitance of the GGAC reaches to 178 F g⁻¹ at a potential scan rate of 500 mV s⁻¹, which is superior to that of commercial activated carbons and ordered mesoporous carbons. The high electrochemical performance of the GGAC is attributed to its good electronic conductivity and high surface area. Partially graphitized activated carbon is a promising electrode material for electrochemical supercapacitors with high rate performance.     

Nitrogen-doped ordered mesoporous carbons based on cyanamide as the dopant for supercapacitor

Nitrogen-doped ordered mesoporous carbons (N-doped OMCs) with a high surface area of 1741 m²/g and nitrogen content up to 15 wt.% have been synthesized by nanocasting approach by using SBA-15 as a hard template, phenolic resin (resol) as a carbon source and high nitrogen-containing cyanamide as the nitrogen dopant. The introduction of cyanamide not only incorporates high-content nitrogen into the carbon matrix in the primary forms of pyridinic and quaternary species, but also greatly increases the surface area of materials. The obtained N-doped OMCs have large surface area with mesoporosity up to 92%, uniform and appropriate pore size (3.6–4.1 nm), large pore volume (1.2–1.81 cm³/g). These merits together with high nitrogen enrichment lead to a specific capacitance (230 F/g at 0.5 A/g) and good rate capability (175 F/g at 20 A/g with capacitance retention of 77.4%) in 6 M KOH aqueous electrolytes.     

Preparation of porous carbon nanofibers derived from graphene oxide/polyacrylonitrile composites as electrochemical electrode materials

Porous carbon nanofibers (CNFs) derived from graphene oxide (GO) were prepared from the carbonization of electrospun polyacrylonitrile nanofibers with up to 15 wt.% GO at 1200 °C, followed by a low-temperature activation. The activated CNFs with reduced GOs (r-GO) revealed a specific surface area and adsorption capacity of 631 m²/g and 191.2 F/g, respectively, which are significantly higher than those of pure CNFs (16 m²/g and 3.1 F/g). It is believed that rough interfaces between r-GO and CNFs introduce oxygen pathways during activation, help to produce large amounts of all types of pores compared to pure activated CNFs.     

Synthesis and characterization of mesoporous carbon through inexpensive mesoporous silica as template

Mesoporous silica materials have been synthesized through sol–gel reaction using inexpensive sodium silicate as source of silica and low cost hydroxy carboxylic acid compounds as templates/pore forming agents. The material measured surface area of 1014 m²/g, pore diameter of 65 Å and pore volume of 1.4 cc/g when parameters like time and temperature of synthesis along with mole ratio of TA/SiO₂ were optimized. Here TA stands for tartaric acid. Carbonization of sucrose inside the pores of above silica material at 900 °C followed by removal of silica framework using aqueous ethanoic solution of NaOH gave rise to mesoporous carbon material. The resulting materials were characterized by N₂-sorption, FTIR spectroscopy, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, thermal analysis and cyclic voltammetry. Three dimensional interconnecting wormhole channel arrangement of mesoporous silica template leads to mesoporous carbon replica with surface area of 1200 m²/g. X-ray photoelectron spectroscopic study (XPS) of the mesoporous carbon material shows the concentration of carbon atom in the range of 97–98% with 1–2% oxygen and negligible amount of silica. The electrochemical double layer capacitance behavior of carbon material with the specific capacitance value of 88.0 F/g at the scan rate of 1 mV/s appears to be promising.     

The production of an electrochemical capacitor electrode using holey single-wall carbon nanohorns with high specific surface area

We prepared single-wall carbon nanohorns (SWCNHs) with a high specific surface area and fabricated an electrochemical capacitor electrode with good performance from them. Carbon impurities involved in the as-grown SWCNHs were thoroughly removed and the purified SWCNHs were oxidized to produce holes in them (SWCNHox). The specific surface area was estimated as 1720 m²/g, the largest surface area of SWCNHs ever reported. Capacitive properties were also investigated using the obtained SWCNHox. We found that an electrochemical device with SWCNHox showed an excellent specific capacitance of about 100 F/g, accelerating industrial progress for their uses in energy and environmental fields.     

Improved cyclability of lithium–sulfur battery cathode using encapsulated sulfur in hollow carbon nanofiber@nitrogen-doped porous carbon core–shell composite

Hollow carbon nanofiber@nitrogen-doped porous carbon (HCNF@NPC) core–shell composite, which was carbonized from HCNF@polyaniline, was prepared as an improved high conductive carbon matrix for encapsulating sulfur as a cathode composite material for lithium–sulfur batteries. The prepared HCNF@NPC-S composite with high sulfur content of 77.5 wt.% showed an obvious core–shell structure with an NPC layer coating on the surface of the HCNFs and sulfur homogeneously distributed in the coating layer. This material exhibited much better electrochemical performance than the HCNF-S composite, delivered initial discharge capacity of 1170 mAh g⁻¹, and maintains 590 mAh g⁻¹ after 200 cycles at the current density of 837.5 mA g⁻¹ (0.5 C). The significantly improved electrochemical performance of the HCNF@NPC-S composite was attributed to the synergetic effect between HCNF cores, which provided electronic conduction pathways and worked as mechanical support, and the NPC shells with relatively high surface area and pore volume, which could trap sulfur/polysulfides and provide Li⁺ conductive pathways.     

Synthesis of large area carbon nanosheets for energy storage applications

We report the large area growth of highly conductive carbon nanosheets (CNS) composed of few layer graphene on 200 mm diameter Si substrates using conventional radio frequency plasma-enhanced chemical vapour deposition. Raman spectroscopy is used to characterise the evolution of the CNS nucleation and growth with time in conjunction with TEM revealing the nano-sized graphene-like nature of these films and the intimate contact to the substrate. An individual sheet can have edges as thin as 3 graphene layers. The influence of the growth support layer is also discussed as film growth is compared on titanium nitride (TiN) and directly on Si. Electrochemical cyclic voltammogram (CV) measurements reveal these layers to form an excellent electrical contact to the underlying substrate with excellent stability towards oxidation whilst having a large electrochemical surface area. The resistance of a 150 nm film was measured to be as low as 20 μohm cm. The high percentage of narrow few layer graphene edge sites exposed allows for faster electrochemical reaction rates compared to carbon nanotubes (CNTs) and other electrode materials (glassy carbon and Pt).     

Electrospun Pt/SnO2 nanofibers as an excellent electrocatalysts for hydrogen oxidation reaction with ORR-blocking characteristic

Pt/SnO₂ nanofibers were synthesized via electrospinning. The unique electrochemical properties were in evidence based on the activity that allowed a hydrogen oxidation reaction and inhibit an oxygen reduction reaction. A high electrochemically active surface area value of 81.17 m²/g-Pt was achieved with ultra-low Pt loading (4.03 wt.%). The kinetics of a hydrogen oxidation reaction was investigated using a linear sweep voltammetry technique under a hydrogen atmosphere. A diffusion-limited current was achieved at 0.07 V and was stable at a high potential. This preparation technique shows great promise for the design of anode electrocatalyst material for fuel cells.     

Electrochemical detection of catechol at integrated carbon nanotubes electrodes

The mechanical stability of the electrode plays a very important role in the long-term stability of electrochemical behavior. In this paper, multi-wall carbon nanotubes (MWCNTs) electrodes were prepared in the holes of glass directly by microwave plasma chemical vapor deposition and the electrochemical behavior of catechol at the integrated MWCNT electrodes was investigated. The oxygen plasma treated CNTs had excellent electrochemical behavior for the analysis of catechol. The catechol was detected in the linear concentration range of 1.0 × 10^− 6 mol L^− 1–1.0 × 10^− 3 mol L^− 1. And because CNTs were integrated directly on the substrate, the stable response to catechol solution showed that the carbon nanotubes electrodes had long-term stability.     

Mesoporous N-containing carbon nanosheets towards high-performance electrochemical capacitors

We developed a direct carbonization strategy to efficiently fabricate mesoporous N-containing carbon nanosheets (N-CNSs) by using polyaniline nanosheets as a carbon precursor. Physicochemical characterizations revealed that the as-synthesized N-CNSs with 5.9 wt.% N species possessed a well-developed mesoporous architecture with large specific surface area of 352 m² g⁻¹, high mesoporous volume of 0.32 cm³ g⁻¹, and average pore size of ∼5.2 nm. When further utilized as an electrode for electrochemical capacitors, the mesoporous N-CNSs delivered a large specific capacitance of 239 F g⁻¹ at 0.5 A g⁻¹, and even 197 F g⁻¹ at a high current load of 8 A g⁻¹, indicating its good rate behavior. Furthermore, the capacitance degradation of ∼4% over continuous 5000 charge–discharge cycles at 6 A g⁻¹ further verified its good electrochemical stability at high rates for long-term electrochemical capacitors application.     

Porous nitrogen-doped carbon vegetable-sponges with enhanced lithium storage performance

Porous nitrogen-doped carbon vegetable-sponges (N-DCSs) have been fabricated by chemical treatment of the Cu@C precursors using HNO₃ for the first time. The obtained N-DCSs are porous three-dimensional (3D)-structure and similar to numerous agglomerated fluffy micro-vegetable-sponges. When the precursors are treated by H₂SO₄, carbon vegetable-sponges (CSs) without nitrogen doping are prepared. As anode materials in lithium ion batteries, the as-prepared N-DCSs show improved Li-storage capacity and cycling stability as compared with the pure CSs. They offer 870 mA h g⁻¹ at 0.5 A g⁻¹ after 300 cycles and high reversible capacity with 910 mA h g⁻¹ at 0.2 A g⁻¹ after cycled at different current densities, which are much higher than those of CSs. It is envisaged that the large surface area, unique 3D porous nanostructure and appropriate nitrogen doping are favorable for the superior electrochemical properties of N-DCSs.     

A novel ultra-light reticulated SiC foam with hollow skeleton

In this study, ultra-light reticulated SiC foam (SF) with hollow skeleton was prepared by applying chemical vapor deposition technique to deposit SiC layer on carbon foam (CF) skeleton, followed by high temperature oxidation of CF. The microstructures of materials were examined by SEM and SF samples show higher specific surface area (349 ± 13 m²/g), initial oxidation temperature (1000 °C) and compressive stress (0.6 MPa) than CF. The compression test results show that the compressive strength of SF increased with the CVD time. While the compressive strength decreased significantly, when the CVD temperature reached 1200 °C. Keeping in view superior observed related characteristics, the prepared SF with special structures was anticipated to be suitable for catalysis, energy storage or membrane science.