High performance of nanoporous carbon in cryogenic hydrogen storage and electrochemical capacitance

Nanoporous carbon materials were synthesized by a two-step casting process using zeolite 13X as template. The nanoporous structures were characterized by X-ray diffraction, high resolution transmission electron microcopy and nitrogen sorption at 77 K, and the results show that pore filling in the zeolite channels could play an important role in the replication of zeolite-like structural order. Better pore filling led to a more ordered structure as well as higher surface area and pore volume. Further potassium hydroxide (KOH) activation improved the microporous texture to the carbon framework and resulted in higher surface area and pore volume. A large hydrogen uptake capacity of 6.30 wt.% has been achieved at 77 K and 20 bar. Besides, a high gravimetric capacitance of up to 160 F g⁻¹ and an energy density of 30 W h kg⁻¹ have been obtained when tested as an electrode for supercapacitors. The high performance in cryogenic hydrogen storage and electrochemical capacitance were closely correlated with the pore structures of the carbon materials.     

Polyfurfuryl alcohol derived activated carbons for high power electrical double layer capacitors

Polyfurfuryl alcohol (PFA) derived activated carbons were prepared by the acid catalysed polymerization of furfuryl alcohol, followed by potassium hydroxide activation. Activated carbons with apparent BET surface areas ranging from 1070 to 2600 m² g⁻¹, and corresponding average micropore sizes between 0.6 and 1.6 nm were obtained. The porosity of these carbons can be carefully controlled during activation and their performance as electrode materials in electric double layer capacitors (EDLCs) in a non-aqueous electrolyte (1 M Et₄NBF₄/ACN) is investigated.Carbon materials with a low average pore size (<∼0.6 nm) exhibited electrolyte accessibility issues and an associated decrease in capacitance at high charging rates. PFA carbons with larger average pore sizes exhibited greatly improved performance, with specific electrode capacitances of 150 F g⁻¹ at an operating voltage window of 0-2.5 V; which corresponds to 32 Wh kg⁻¹ and 38 kW kg⁻¹ on an active material basis. These carbons also displayed an outstanding performance at high current densities delivering up to 100 F g⁻¹ at current densities as high as 250 A g⁻¹. The exceptionally high capacitance and power of this electrode material is attributed to its good electronic conductivity and a highly effective combination of micro- and fine mesoporosity.     

High capacitance properties of polyaniline by electrochemical deposition on a porous carbon substrate

Electrochemical deposition of polyaniline (PANI) is carried out on a porous carbon substrate for supercapacitor studies. The effect of substrate is studied by comparing the results obtained using platinum, stainless steel and porous carbon substrates. PANI deposited at 100 mV s⁻¹ sweep rate by potentiodynamic technique on porous carbon substrate is found to possess superior capacitance properties. Experimental variables, namely, concentrations of aniline monomer and H₂SO₄ supporting electrolyte are varied and arrived at the optimum concentrations to obtain a maximum capacitance of PANI. Low concentrations of both aniline and H₂SO₄, which produce PANI at low rates, are desirable. The PANI deposits prepared under these conditions possess network morphology of nanofibrils. Capacitance values as high as 1600 F g⁻¹ are obtained and PANI coated carbon electrodes facilitate charge-discharge current densities as high as 45 mA cm⁻² (19.8 A g⁻¹). Electrodes are found to be fairly stable over a long cycle-life, although there is some capacitance loss during the initial stages of cycling.     

Electrochemical performance of CoSb3/MWNTs nanocomposite prepared by in situ solvothermal synthesis

In situ solvothermally synthesized composite (SSC) and mechanically blended composite (MBC) of nanosized CoSb₃ and multiwalled carbon nanotubes (MWNTs) were prepared and investigated as potential anode materials for Li-ion batteries. It was found that SSC exhibits an entanglement structure of nanosized CoSb₃ and MWNTs and shows significantly better cycling stability than MBC. The reversible capacity of SSC electrode reaches 312 mA h g⁻¹ at the first cycle and remains above 265 mA h g⁻¹ after 30 cycles.     

Polyaniline nanofibers obtained by interfacial polymerization for high-rate supercapacitors

Polyaniline (PANI) nanofibers were fabricated by interfacial polymerization in the presence of para-phenylenediamine (PPD). The additives cannot only have a profound impact on the polymers morphology, but can also improve their specific energy and specific capacitances. It was found that PANI nanofibers prepared in the presence of PPD were longer and less entangled than those in the absence of PPD due to a much faster polymerization rate in initial stage. A specific capacitance value of 548 F g⁻¹, a specific power value of 127 W kg⁻¹ and a specific energy value of 36 Wh kg⁻¹ were obtained in polyaniline nanofibers prepared in the present of PPD at a constant discharge current density of 0.18 A g⁻¹.     

Ultra-high specific capacitance of self-doped 3D hierarchical porous turtle shell-derived activated carbon for high-performance supercapacitors

The turtle shell of biomass waste is used as raw material, and the natural inorganic salt contained in it is used as a salt template in combination with a chemical activation method to successfully prepare a high-performance activated carbon with hierarchical porous structure. The role of hydroxyapatite (HAP) and KOH in different stages of preparation was investigated. The prepared turtle shell-derived activated carbon (TSHC-5) has a well-developed honeycomb pore structure, which gives it a high specific surface area (SSA) of 2828 m² g^?1 with a pore volume of 1.91 cm³ g^?1. The excellent hierarchical porous structure and high heteroatom content (O 6.88%, N 5.64%) allow it to have an ultra-high specific capacitance of 727.9 F g^?1 at 0.5 A g^?1 with 92.27% of capacitance retention even after 10,000 cycles. Excitingly, the symmetric supercapacitor assembled from TSHC-5 activated carbon exhibits excellent energy density and cycling stability in a 1 M Na₂SO₄ aqueous solution. The energy density is 45.1 Wh·kg^?1 at a power density of 450 W kg^?1, with 92.05% capacitance retention after 10,000 cycles. Therefore, turtle shell-derived activated carbon is extremely competitive in sustainable new green supercapacitor electrode materials.     

Preparation of a graphene nanosheet/polyaniline composite with high specific capacitance

A graphene nanosheet (GNS)/polyaniline (PANI) composite was synthesized using in situ polymerization. The morphology and microstructure of samples were examined by scanning electron microscopy (SEM), transition electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. Electrochemical properties were characterized by cyclic voltammetry (CV) and galvanostatic charge/discharge. GNS as a support material could provide more active sites for nucleation of PANI as well as excellent electron transfer path. The GNS was homogeneously coated on both surfaces with PANI nanoparticles (∼2 nm), and a high specific capacitance of 1046 F g⁻¹ (based on GNS/PANI composite) was obtained at a scan rate of 1 mV s⁻¹ compared to 115 F g⁻¹ for pure PANI. In addition, the energy density of GNS/PANI composite could reach 39 W h kg⁻¹ at a power density of 70 kW kg⁻¹.     

A novel nickel-based mixed rare-earth oxide/activated carbon supercapacitor using room temperature ionic liquid electrolyte

Mesopore nickel-based mixed rare-earth oxide (NMRO) and activated carbon (AC) with rich oxygen-contained groups were prepared as electrode materials in a supercapacitor using room temperature ionic liquid (RTIL) electrolyte. These electrode materials were characterized by XPS, XRD, N₂ adsorption, SEM as well as various electrochemical techniques, and showed good properties and operated well with RTIL electrolyte. A 3 V asymmetrical supercapacitor was fabricated, which delivered a real power density of 458 W kg⁻¹ as well as a real energy density of 50 Wh kg⁻¹, and during a 500-cycle galvanostatic charge/discharge measurement, no capacity decay was visible. Such promising energy-storage performance was to a large extent ascribed to nonvolatile RTIL electrolyte with wide electrochemical windows and high stable abilities worked with both electrode materials.     

Highly mesoporous carbonaceous material of activated carbon beads for electric double layer capacitor

The activated carbon beads (ACB) are prepared by a new preparation method, which is proposed by mixing the coal tar pitch and fumed silica powder at a certain weight ratio and activation by KOH at different weight ratios and different temperatures. The BET surface area, pore volume and average pore size are obtained based on the nitrogen adsorption isotherms at 77 K by using ASAP 2010 apparatus. The results show that our samples have much high specific surface area (SSA) of 3537 m² g⁻¹and high pore volume value of 3.05 cm³ g⁻¹. The percentage of mesopore volume increases with the weight ratio of KOH/ACB ranging from 4% to 72%. The electrochemical double layer capacitors (EDLCs) are assembled with resultant carbon electrode and electrolyte of 1 mol L⁻¹ Et₄NBF₄/PC. The specific capacitance of the ACB sample could be as high as 191.7 F g⁻¹ by constant current charge/discharge technique, indicating that the ACB presents good characteristics prepared by the method proposed in this work. The investigation of influence of carbon porosity structure on capacitance indicates that the SSA plays an important role on the capacitance and all the pore sizes of less than 1 nm, from 1 to 2 nm and larger than 2 nm contribute to the capacitance. Mesopore structure is beneficial for the performance at high current density.     

Influence of oxidation process on the adsorption capacity of activated carbons from lignocellulosic precursors

A set of activated carbon materials non-oxidised and oxidised, were successfully prepared from two different lignocellulosic precursors, almond shell and vine shoot, by physical activation with carbon dioxide and posterior oxidation with nitric acid. All samples were characterised in relation to their structural properties and chemical composition, by different techniques, namely nitrogen adsorption at 77 K, elemental analysis (C, H, N, O and S), point of zero charge (PZC) and FTIR. A judicious choice was made to obtain carbon materials with similar structural properties (apparent BET surface area ∼ 850-950 m²g⁻¹, micropore volume ∼ 0.4 cm³g⁻¹, mean pore width ∼ 1.2 nm and external surface area ∼ 14-26 m²g⁻¹). After their characterisation, these microporous activated carbons were also tested for the adsorption of phenolic compounds (p-nitrophenol and phenol) in the liquid phase at room temperature. The performance in liquid phase was correlated with their structural and chemical properties. The oxidation had a major impact at a chemical level but only a moderate modification of the porous structure of the samples. The Langmuir and Freundlich equations were applied to the experimental adsorption isotherms of phenolic compounds with good agreement for the different estimated parameters.     

High-capacitance carbon electrode prepared by PVDC carbonization for aqueous EDLCs

Porous carbons with high-volumetric capacitance in aqueous electric double layer capacitors (EDLCs) were simply prepared by poly(vinylidene chloride) (PVDC) carbonization at high temperature without activation or any other additional processes. The PVDC-derived carbon is microporous with Brunauer-Emmett-Teller (BET) surface area about 1200 m² g⁻¹. As it possesses not only high-gravimetric capacitance (262 F g⁻¹) but also high-electrode density (0.815 g cm⁻³), the PVDC-derived carbon present an outstanding high-volumetric capacitance of 214 F cm⁻³, twice over of the commercial carbon Maxsorb-3 with a high-surface area of 3200 m² g⁻¹. The PVDC-derived carbon also exhibit good rate performance, indicating that it is a promising electrode material for EDLCs.     

Characterisation of activated nanoporous carbon for supercapacitor electrode materials

Commercial nanoporous carbon RP-20 was activated with water vapor in the temperature range from 950 °C to 1150 °C. The XRD analysis was carried out on nanoporous carbon powder samples to investigate the structural changes (graphitisation) in modified carbon that occurred at activation temperatures T ? 1150 °C. The first-order Raman spectra showed the absorption peak at 1582 cm⁻¹ and the disorder (D) peak at 1350 cm⁻¹. The low-temperature N₂ adsorption experiments were performed at −196 °C and a specific surface area up to 2240 m²g⁻¹ for carbon activated at T = 1050 °C was measured. The cell capacitance for two electrode activated nanoporous carbon system advanced up to 60 F g⁻¹ giving the specific capacitance ∼240 F g⁻¹ to one electrode nanoporous carbon ∣1.2 M (C₂H₅)₃CH₃NBF₄ + acetonitrile solution interface. A very wide region of ideal polarisability for two electrode system (∼3.2 V) was achieved. The low frequency limiting specific capacitance very weakly increases with the rise of specific area explained by the mass transfer limitations in the nanoporous carbon electrodes. The electrochemical characteristics obtained show that some of these materials under discussion can be used for compilation of high energy density and power density non-aqueous electrolyte supercapacitors with higher power densities than aqueous supercapacitors.     

Effect of pore size distribution of coal-based activated carbons on double layer capacitance

A series of coal-based activated carbons representing a wide range of mesopore content, from 16.7 to 86.9%, were investigated as an electrode in electric double layer capacitors (EDLCs) in 1 mol l⁻¹ H₂SO₄ and 6 mol l⁻¹ KOH electrolytic solutions. The activated carbons (ACs) used in this study were produced from chemically modified lignite, subbituminous and bituminous coals by carbonization and subsequent activation with steam. The BET surface area of ACs studied ranged from 340 to 1270 m² g⁻¹. The performance of ACs as EDLC electrodes was characterized using voltammetry, galvanostatic charge/discharge and impedance spectroscopy measurements. For the carbons with surface area up to 1000 m² g⁻¹, the higher BET surface area the higher specific capacitance (F g⁻¹) for both electrolytes. The surface capacitance (μF cm⁻²) increases also with the mesopore content. The optimum range of mesopore content in terms of the use of ACs studied for EDLCs was found to be between 20 and 50%. A maximum capacitance exceeding 160 F g⁻¹ and a relatively high surface capacitance about 16 μF cm⁻² measured in H₂SO₄ solution were achieved for the AC prepared from a sulfonated subbituminous coal. This study shows that the ACs produced from coals exhibit a better performance as an electrode material of EDLC in H₂SO₄ than in KOH electrolytic solutions. For KOH, the capacitance per unit mesopore surface is slightly lower than that referred to unit micropore surface (9.1 versus 10.1 μF cm⁻²). However, in the case of H₂SO₄ the former capacitance is double and even higher compared with the latter (23.1 versus 9.8 μF cm⁻²). On the other hand, the capacitance per micropore surface area is the same in both electrolytes used, about 10.0 μF cm⁻².     

Improvement of the structural and chemical properties of a commercial activated carbon for its application in electrochemical capacitors

The present paper shows that the performance of an inexpensive activated carbon used in electrochemical capacitors can be significantly enhanced by a simple treatment with KOH at 850 °C. The changes in the specific surface area, as well as in the surface chemistry, lead to high capacitance values, which provide a noticeable energy density.The KOH-treatment of a commercial activated carbon leads to highly pure carbons with effective surface areas in the range of 1300-1500 m² g⁻¹ and gravimetric capacitances as high as three times that of the raw carbon.For re-activated carbons, one obtains at low current density (50 mA g⁻¹) values of 200 F g⁻¹ in aqueous electrolytes (1M H₂SO₄ and 6M KOH) and around 150 F g⁻¹ in 1M (C₂H₅)₄NBF₄ in acetonitrile. Furthermore, the resulting carbons present an enhanced and stable performance for high charge/discharge load in organic and aqueous media.This work confirms the possibilities offered by immersion calorimetry on its own for the prediction of the specific capacitance of carbons in (C₂H₅)₄NBF₄/acetonitrile. On the other hand, it also shows the limitations of this technique to assess, with a good accuracy, the suitability of a carbon to be used as capacitor electrodes operating in aqueous electrolytes (H₂SO₄ and KOH).     

LiPF6 based ethylene carbonate-dimethyl carbonate electrolyte for high power density electrical double layer capacitor

Electrochemical characteristics of the electrical double layer capacitor based on the two identical microporous carbide derived carbon C(TiC 950) electrodes in 1 M LiPF₆ ethylene carbonate-dimethyl carbonate (1:1 by volume) mixture have been studied using cyclic voltammetry and electrochemical impedance spectroscopy. Specific capacitance, phase angle, series and parallel resistances, characteristic time constant, energy and power densities etc. have been calculated and found to be dependent on the cell potential applied. Wide region of ideal polarisability ΔE ≤ 3.2 V, short characteristic time constant and high limiting capacitance 129 F g⁻¹, complex power and maximal energy and power density values have been obtained, indicating that this electrolyte can be used for high energy and power density supercapacitors. Additionally, the supercapacitors based on the partially graphitized C(VC) (applied as negatively charged electrode) and amorphous C(TiC 950) (applied as positively charged electrode) were completed and tested. The calculated energy and power densities were for asymmetrical C(VC 1100)|C(TiC 950)|1 M LiPF₆ + EC + DMC cell 26.2 Wh kg⁻¹ and 57.2 kW kg⁻¹, respectively, but for symmetrical C(TiC 950)|C(TiC 950)|1 M LiPF₆ + EC + DMC cell somewhat higher energy density 36.7 Wh kg⁻¹ and power density 83.6 kW kg⁻¹ values were established.     

Electrodeposited PbO2 thin film as positive electrode in PbO2/AC hybrid capacitor

Lead dioxide (PbO₂) thin films were prepared on Ti/SnO₂ substrates by means of electrodeposition method. Galvanostatic technique was applied in PbO₂ film formation process, and the effect of deposition current on morphology and crystalline form of the PbO₂ thin films was studied by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The energy storage capacity of the prepared PbO₂ electrode was investigated by means of cyclic voltammetry (CV) and charge/discharge cycles, and a rough surface structure PbO₂ film was selected as positive electrode in the construction of PbO₂/AC hybrid capacitor in a 1.28 g cm⁻³ H₂SO₄ solution. The electrochemical performance was determined by charge/discharge tests and electrochemical impedance spectroscopy (EIS). The results showed that the PbO₂/AC hybrid capacitor exhibited high capacitance, good cycling stability and long cycle life. In the voltage range of 1.8-0.8 V during discharge process, considering the weight of all components of the hybrid capacitor, including the two electrodes, current collectors, H₂SO₄ electrolyte and separator, the specific energy and power of the device were 11.7 Wh kg⁻¹ and 22 W kg⁻¹ at 0.75 mA cm⁻², and 7.8 Wh kg⁻¹ and 258 W kg⁻¹ at 10 mA cm⁻² discharge currents, respectively. The capacity retains 83% of its initial value after 3000 deep cycles at the 4 C rate of charge/discharge.     

Large reversible capacity of high quality graphene sheets as an anode material for lithium-ion batteries

High quality graphene sheets were prepared from graphite powder through oxidation followed by rapid thermal expansion in nitrogen atmosphere. The preparation process was systematically investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and Brunauer-Emmett-Teller (BET) measurements. The morphology and structure of graphene sheets were characterized by scanning electron microscope (SEM) and high-resolution transmission electron microscopy (HRTEM). The electrochemical performances were evaluated in coin-type cells versus metallic lithium. It is found that the graphene sheets possess a curled morphology consisting of a thin wrinkled paper-like structure, fewer layers (∼4 layers) and large specific surface area (492.5 m² g⁻¹). The first reversible specific capacity of the prepared graphene sheets was as high as 1264 mA h g⁻¹ at a current density of 100 mA g⁻¹. Even at a high current density of 500 mA g⁻¹, the reversible specific capacity remained at 718 mA h g⁻¹. After 40 cycles, the reversible capacity was still kept at 848 mA h g⁻¹ at the current density of 100 mA g⁻¹. These results indicate that the prepared high quality graphene sheets possess excellent electrochemical performances for lithium storage.     

Preparation and capacitive properties of cobalt-nickel oxides/carbon nanotube composites

In this paper, nickel-cobalt oxides/carbon nanotube (CNT) composites were prepared by adding and thermally decomposing nickel and cobalt nitrates directly onto the surface of carbon nanotube/graphite electrode to form nickel and cobalt oxides. Carbon nanotubes used in this paper were grown directly on graphite substrate by chemical vapor deposition technique. The capacitive behavior of nickel-cobalt oxides/CNT electrode was investigated by cyclic voltammetry and galvanostatic charge-discharge method in 1 M KOH aqueous solutions. The results show that nickel-cobalt oxides/CNT composite electrode has excellent charge-discharge cycle stability (0.2% and 3.6% losses of the specific capacitance are found at the 1000th and 2000th charge-discharge cycles, respectively) and good charge-discharge properties at high currrent density. Additionally, the effect of Ni/Co molar ratio on specific capacitance of the composite electrode was investigated and the highest specific capacitance (569 F g⁻¹ at 10 mA cm⁻²) is obtained at Ni/Co molar ratio = 1:1.     

On the performances of lead dioxide and boron-doped diamond electrodes in the anodic oxidation of simulated wastewater containing the Reactive Orange 16 dye

The performances of the Ti-Pt/β-PbO₂ and boron-doped diamond (BDD) electrodes in the electrooxidation of simulated wastewaters containing 85 mg L⁻¹ of the Reactive Orange 16 dye were investigated using a filter-press reactor. The electrolyses were carried out at the flow rate of 7 L min⁻¹, at different current densities (10-70 mA cm⁻²), and in the absence or presence of chloride ions (10-70 mM NaCl). In the absence of NaCl, total decolourisation of the simulated dye wastewater was attained independently of the electrode used. However, the performance of the BDD electrode was better than that of the Ti-Pt/β-PbO₂ electrode; the total decolourisations were achieved by applying only 1.0 A h L⁻¹ and 2.0 A h L⁻¹, respectively. In the presence of NaCl, with the electrogeneration of active chlorine, the times needed for total colour removal were markedly decreased; the addition of 50 mM Cl⁻ or 35 mM Cl⁻ (for Ti-Pt/β-PbO₂ or BDD, respectively) to the supporting electrolyte led to a 90% decrease of these times (at 50 mA cm⁻²). On the other hand, total mineralization of the dye in the presence of NaCl was attained only when using the BDD electrode (for 1.0 A h L⁻¹); for the Ti-Pt/β-PbO₂ electrode, a maximum mineralization of 85% was attained (for 2.0 A h L⁻¹). For total decolourisation of the simulated dye wastewater, the energy consumption per unit mass of dye oxidized was only 4.4 kWh kg⁻¹ or 1.9 kWh kg⁻¹ using the Ti-Pt/β-PbO₂ or BDD electrode, respectively. Clearly the BDD electrode proved to be the best anode for the electrooxidative degradation of the dye, either in the presence or absence of chloride ions.     

Synthesis and characterization of 10Sc1CeSZ powders prepared by a solid–liquid method for electrolyte-supported solid oxide fuel cells

10Sc1CeSZ is one of the most important electrolyte materials used for solid oxide fuel cells (SOFCs). A novel solid–liquid method (SLM) was adopted for the preparation of 10Sc1CeSZ nanopowder. High-purity, single-phase, homogeneous 10Sc1CeSZ powder was successfully prepared using this method. The resulting powders and ceramic pellets were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). A cubic structure was obtained when the value of the specific surface area (SSA) of the starting material ZrO₂ was greater than 60 m² g⁻¹. A conductivity of 0.14 S cm⁻¹ at 800 °C was achieved for the sintered pellets. The performance of the electrolyte-supported cell (ESC) NiO+GDC/10Sc1CeSZ /10Sc1CeSZ +LSM reached 0.66 W cm⁻² at 0.75 V and 850 °C.