Hybrid electrochemical capacitors based on polyaniline and activated carbon electrodes

The performance of a newly designed, polyaniline–activated carbon, hybrid electrochemical capacitor is evaluated. The capacitor is prepared by using polyaniline as a positive electrode and activated carbon as a negative electrode. From a constant charge–discharge test, a specific capacitance of 380 F g⁻¹ is obtained. The cycling behaviour of the hybrid electrochemical capacitor is examined in a two-electrode cell by means of cyclic voltammetry. The cycle-life is 4000 cycles. Values for the specific energy and specific power of 18 Wh kg⁻¹ and 1.25 kW kg⁻¹, respectively, are demonstrated for a cell voltage between 1 and 1.6 V.     

Multilayered Sn–Zn–Cu alloy thin-film as negative electrodes for advanced lithium-ion batteries

Sn-based alloy compounds have been considered as possible alternatives for carbon in lithium-ion batteries and attract great attentions because of their large electrochemical capacity compared with that of carbon. In this work, a multilayered Sn–Zn/Zn/Cu alloy thin-film electrode has been prepared by electroplating method. The structure and performance of the electrode before and after heat treatment have been investigated. It is found that Cu₆Sn₅ phase and multilayered structure in electrode are formed after heat treatment. This optimized structure of the heat-treated electrode results in enhanced cycle life. The capacity of the electrode is over 320 mA h g⁻¹ after 100 cycles; though it is 83 mA h g⁻¹ after 20 cycles for as-plated electrode. The Sn–Cu and Zn–Cu alloy formed a network in the electrode is considered to strengthen the electrode and reduce the effect of volume expansion and phase transition during cycling. Experimental results also reveal that lower cut-off potential (0.05 V) for charging and higher one (1.2 V) for discharging result in long cycle life and high discharge capacity, respectively. The reason of capacity decay of the heat-treatment electrode during cycling has also been investigated. All these results show that the electroplated Sn–Zn-based alloy film on Cu foil would be a promising negative material with high capacity and low cost for Li secondary batteries.     

Finite element simulation of heat and mass transfer in activated carbon hydrogen storage tank

A mathematical model of heat and mass transfer in activated carbon (AC) tank for hydrogen storage is proposed based on a set of partial differential equations (PDEs) controlling the balances or conservations of mass, momentum and energy in the tank. These PDEs are numerically solved by means of the finite element method using Comsol Multiphysics^TM. The objective of this paper is to establish a correct set of PDEs describing the physical system and appropriate parameters for simulating the hydrogen storage process. In this paper, we establish an axisymmetric model of hydrogen storage by adsorption on activated carbon, considering heat and mass transfer of hydrogen in storage tank during the charging process at room temperature (295 K) and the pressure of 10 MPa. To simulate the hydrogen storage process accurately, the heat capacity of adsorbed phase, the contact thermal resistance between the AC bed and the steel wall and the inertial resistance of high speed charging hydrogen gas are all taken into account in the model. The governing equations describing the hydrogen storage process by adsorption are solved to obtain the pressure changes, temperature distributions and adsorption dynamics in the storage tank. The pressure reaches a maximum value of 10 MPa at about 240 s. A small downward trend appears in the later stage of the charging process, which lasts 700 s. The temperature distribution is highest in the center of the tank. The temperature history exhibits a rapid increase initially, followed by a steady decline. A modified Dubinin–Astakhov (D–A) model is used to represent the hydrogen adsorption isotherms. The highest hydrogen uptake is 10 mol H₂/kg AC, at the entrance of hydrogen storage tank, where the temperature is lowest. The adsorption distribution at a given time is mainly determined by the temperature distribution, because the pressure is almost uniform in the tank. The adsorption history, however, is dominated by the pressure history because the pressure change is much larger than temperature change during the charging process of hydrogen storage.     

Electrochemical profile of nano-particle CoAl double hydroxide/active carbon supercapacitor using KOH electrolyte solution

A nano-structured CoAl double hydroxide with an average particle size of 60–70 nm was prepared by a chemical co-precipitation. It was used as a positive electrode for the asymmetric hybrid supercapacitor in combination with an active carbon negative electrode in KOH electrolyte solution. The electrochemical capacitance performance of this kind of hybrid supercapacitor was investigated by means of cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge tests. A specific capacitance of 77 F g⁻¹ with a specific energy density of 15.5 wh kg⁻¹ was obtained for the hybrid supercapacitor within the voltage range of 0.9–1.5 V. The supercapacitor also exhibits a good cycling performance and keep 90% of initial capacity over 1000 cycles.     

Formation and characterization of Cu–Si nanocomposite electrodes for rechargeable Li batteries

We have investigated the structural and electrochemical properties of Cu–Si nanocomposite electrode fabricated by co-sputtering method. Reversible capacity of an amorphous Si electrode is degraded continuously with increasing cycle number up to 40 cycles. However, a Cu–Si nanocomposite electrode, where Cu nano-dots are embedded in an amorphous Si matrix, shows an excellent reversible capacity with a stable value of ca. 400 μA h cm⁻² μm⁻¹ up to 40 cycles. The improved reversible capacity of the Cu–Si nanocomposite electrodes is attributed to the enhanced structural stability of the electrodes due to the presence of the Cu nano-dots evenly distributed throughout the Si matrix.     

Effects of electrolytes and electrochemical pretreatments on the capacitive characteristics of activated carbon fabrics for supercapacitors

The capacitive characteristics of activated carbon fabrics (ACFs) coated on the graphite substrates were systematically investigated by means of cyclic voltammetry and the galvanostatic charge–discharge technique. Effects of the PVDF contents in the electronically conductive binder, electrochemical pretreatments, and the electrolytes on the capacitive performance of ACFs were compared in aqueous media. These ACF-pasted electrodes showed the more ideally capacitive responses in 1 M NaNO₃ with a specific capacitance of 76 F g⁻¹ when the electronically conductive binder contained 40 wt.% PVDF. The specific capacitance of ACF-pasted electrodes reached a maximum in 0.5 M H₂SO₄ (about 153 F g⁻¹ measured at 25 mV s⁻¹), due to the presence of a suitable density of oxygen-containing functional groups, when they were subjected to the potentiostatic polarization at 1.8 V (versus reversible hydrogen electrode (RHE)) or potentio-dynamic polarization between 1.3 and 1.8 V in NaNO₃ for 20 min. The oxygen-containing functional groups within the electrochemically pretreated ACFs were identified by means of X-ray photoelectron spectroscopy (XPS).     

Carbon anode for dry-polymer electrolyte lithium batteries

A spherical carbon material of meso-carbon microbead (MCMB) was examined as an anode in a polyethylene oxide (PEO) based polymer electrolyte lithium battery. The electrochemical performance of the carbon electrode with the polymer electrolyte depended on the electrode thickness and the particle size of MCMB. The 30 μm-thick electrode of MCMB with the particle size of 20–30 μm showed a reversible capacity comparable with that in a liquid electrolyte, but the 100 μm-thick electrode showed a half of the 30 μm-thick electrode. The smaller particle size of 5–8 μm exhibited a high irreversible capacity at the first charge–discharge cycle. The reaction heat between MCMB and the polymer electrolyte was 0.5 J mAh^?1, which was much lower compared to those between lithium metal and the polymer electrolyte, 1.2 J mAh^?1, and MCMB and conventional liquid electrolyte, 4.3 J mAh^?1.     

Activation of polymer blend carbon nanofibres by alkaline hydroxides and their hydrogen storage performances

In the present work we study the hydroxide activation (NaOH and KOH) of phenol-formaldehyde resin derived CNFs prepared by a polymer blend technique to prepare highly porous activated carbon nanofibres (ACNFs). Morphology and textural characteristics of these ACNFs were studied and their hydrogen storage capacities at 77 K (at 0.1 MPa and at high pressures up to 4 MPa) were assessed, and compared, with reported capacities of other porous carbon materials.Phenol-formaldehyde resin derived carbon fibres were successfully activated with these two alkaline hydroxides rendering highly microporous ACNFs with reasonable good activation process yields up to 47 wt.% compared to 7 wt.% yields from steam activation for similar surface areas of 1500 m²/g or higher. These nano-sized activated carbons present interesting H₂ storage capacities at 77 K which are comparable, or even higher, to other high quality microporous carbon materials. This observation is due, in part, to their nano-sized diameters allowing to enhance their packing densities to 0.71 g/cm³ and hence their resulting hydrogen storage capacities.     

High rate lithium intercalation properties of V2O5/carbon/ceramic-filler composites

Composite electrodes of amorphous vanadium pentoxide/carbon/ceramic filler were prepared by mixing vanadium oxide hydrosol, acetone, carbon and ceramic fillers, and by extension on aluminum foil. High rate charge/discharge property of the composite electrode was examined, and the effect of fillers was discussed. The composite electrode had a porous structure, in which pores were 0.5–3 μm in diameter and penetrated through the composite. The composite electrode showed a large capacity of 98 mA h/g-electrode at a high current density of 17.2 mA/cm² (270 A/g-electrode). The relation between discharge capacity and current density was calculated by solving the simplified diffusion equation. The apparent diffusion coefficient of lithium ion in the composite electrode was found to be 10 times larger than that of electrode without fillers.     

Significantly enhanced electrochemical hydrogen storage performance of biomass nanocomposites from Pistacia Atlantica modified by CuO nanostructures with different morphologies

Pistacia Atlantica biomass was utilized as an activated carbon precursor for the preparation of copper oxide/activated carbon (CuO/AC) nanocomposites and the electrochemical hydrogen storage (EHS) capacities of copper oxide with different morphologies and provided nanocomposites were studied. Further, the influence of copper oxide pores size upon the EHS capacity was studied through chronopotentiometry system. Under 1 mA current, the discharge capacities of CuO nanoflowers (CuO_nf), CuO nanoparticles (CuO_np), Pistacia Atlantica activated carbon (AC), copper oxide nanoflower/activated carbon (CuO_nf/AC), and copper oxide nanoparticle/activated carbon (CuO_np/AC) were reached to 650, 850, 1200, 2000, and 3000 mAh/g after 25 cycles, respectively. Outcomes reveal that the coating of copper oxide upon the AC with different pores size leads to get better discharge capacity. Therefore, produced nanostructures with inexpensive and simple manner can be utilized for EHS and can be applied as Renew. Energy to reduce the use of fossil fuels.     

Effects of Pd substitution on the electrochemical properties of Mg0.9−xTi0.1PdxNi (x = 0.04–0.1) hydrogen storage alloys

Amorphous Mg_0.9−xTi_0.1Pd_xNi (x = 0.04–0.1) hydrogen storage alloys were prepared by mechanical alloying (MA). The effects of Pd substitution on the electrochemical properties of the Mg_0.9−xTi_0.1Pd_xNi (x = 0.04–0.1) electrode alloys were studied by cyclic charge–discharge, linear polarization, anodic polarization, electrochemical impedance spectroscopy (EIS), and hydrogen diffusion coefficient experiments. It was found that the cyclic capacity retention rate C₅₀/C₁ of the quaternary alloys was greatly improved due to the substitution of Pd for Mg. Mg_0.8Ti_0.1Pd_0.1Ni electrode alloy retained the discharge capacity above 200 mAh g⁻¹ even after 80 charge–discharge cycles, possessing the longest cycle life in the studied quaternary alloys. The improvement of cycle life was ascribed to the formation of passive film on the surface of these electrode alloys. X-ray photoelectron spectroscopy (XPS) analysis proved that the passive film was composed of Mg(OH)₂, TiO₂, NiO, and PdO, which synergistically protected the alloy from further oxidation. The Auger Electron Spectroscopy (AES) study revealed that the thickness of passive film increased with augmentation of the Pd content. The electrochemical impedance study of electrode alloys after different cycles demonstrated that the passive film became thicker during cycles and its thickness also increased with Pd content augmentation. It was also found that the augmentation of Pd content resulted in the decrease of exchange current density I₀ and the increase of the charge-transfer resistance R_ct. With increasing the Pd amount in the Mg_0.9−xTi_0.1Pd_xNi (x = 0.04–0.1) electrode alloys, hydrogen diffusion coefficient D was gradually enhanced at first. Then, it decreased with augmentation of cycle due to the growth of passive film on the surface of the alloys.     

Cresol–formaldehyde based carbon aerogel as electrode material for electrochemical capacitor

Carbon aerogels have been prepared through a polycondensation of cresol (Cm) with formaldehyde (F) and an ambient pressure drying followed by carbonization at 900 °C. Modification of the porous structures of the carbon aerogel can be achieved by CO₂ activation at various temperatures (800, 850, 900 °C) for 1–3 h. This process could be considered as an alternative economic route to the classic RF gels synthesis. The obtained carbon aerogels have been attempted as electrode materials in electric double-layer capacitors. The relevant electrochemical behaviors were characterized by constant current charge–discharge experiments, cyclic voltammetry and electrochemical impedance spectroscopy in an electrolyte of 30% KOH aqueous solution. The results indicate that a mass specific capacitance of up to 78 F g⁻¹ for the non-activated aerogel can be obtained at current density 1 mA cm⁻². CO₂ activation can effectively improve the specific capacitance of the carbon aerogel. After CO₂ activation performed at 900 °C for 2 h, the specific capacitance increases to 146 F g⁻¹ at the same current. Only a slight decrease in capacitance, from 146 to 131 F g⁻¹, was observed when the current density increases from 1 to 20 mA cm⁻², indicating a stable electrochemical property of carbon aerogel electrodes in 30% KOH aqueous electrolyte with various currents.     

Recycling of nickel from NiOOH/Ni(OH)2 electrodes of spent Ni–Cd batteries

In this work, nickel from the positive electrode of Ni–Cd batteries was recycled by chemical precipitation and electrodeposition. The structure of the material recovered by chemical precipitation is affected by temperature. Alfa nickel hydroxide is stable at low temperature but becomes beta nickel hydroxide with increasing of the synthesis temperature. Electrodeposition was accomplished by using the galvanostatic technique. The chronopotentiometric plots presented a plateau potential in the initial stage of the deposit growth due to the reduction of ionic nickel. Charge density of the plateau potential and charge efficiency decreased with increase in current density. Charge efficiency around 81.0% was the largest for current densities between 5.0 mA cm⁻² and 10.0 mA cm⁻² for q = 9.0 C cm⁻². As charge density increased to 90.0 C m⁻², the electrodeposition efficiency decreased. In this case, there is a second plateau potential at which the evolution of hydrogen on the nickel electrode, the principal reaction, is quickly reached. Charge density affects not only the reaction kinetics, but also the deposit morphology. A decrease in microporosity is observed with the increase in charge density. The microporosity increases as the current density increases for the same charge density.     

Study on the anode behavior of Sn and Sn–Cu alloy thin-film electrodes

Anodes based on tin metal powder offer large specific capacity, but also exhibit large irreversible capacity and poor cycle performance. In order to use them as a negative electrode for lithium secondary batteries, we focused on the electrodepositing process and investigated an electrodeposited tin layer on copper foil. In the full charge–discharge condition, charging and discharging between 0 and 2.0 V versus Li/Li⁺, the first discharge capacity was 940 mAh g⁻¹, which was 2.5 times as large as that of graphite, and the coulomb efficiency in the first cycle was 93%, but its cycle performance was not improved.In order to enhance the interface strength between the active material and the copper foil, we investigated an anode which was fabricated by annealing an as-deposited anode. In the full charge–discharge condition, the first charge–discharge characteristics were almost equivalent to the as-deposited anode, and the retention capacity ratio after 10 cycles was improved from 20 to 94%. It is considered that this improvement resulted from the formation of two different tin–copper intermetallic compound layers between the tin layer and the copper current collector due to the heat treatment.A small cell using this annealed anode as a negative electrode was also investigated. This cell offered good cycle performance for the first 20 cycles.     

Electrochemical properties of Zn/orange dye aqueous solution/carbon cell

An investigation is made of the electrochemical properties of a Zn/orange dye aqueous solution/carbon cell. In this cell, a solution of 3 wt.% orange dye (C₁₇H₁₇N₅O₂) in distilled water is used as the electrolyte and zinc and carbon rods serve as electrodes. The cell is fabricated in a cylindrical glass vessel and has a length and a diameter of 4 and 2 cm, respectively. The discharge voltage–current, charge voltage/current–time and discharge voltage/current–time studies are made. It is found that the cell is rechargeable. The open-circuit voltage and short-circuit current of the fully charged cell is 1.5 V and 0.45 mA, respectively. The efficiency of current discharge/charge is 67%. The discharge voltage/current–time characteristics exhibit stable and constant behaviour.     

Thermal effect of the adsorption heat on an adsorbed natural gas storage and transportation systems

This paper experimentally studies the thermal effect that results from the adsorption heat on both the charge and discharge performance of adsorbed natural gas (ANG) storage and transportation systems. Two storage tanks built with temperature systems and security control were used during the adsorption and desorption process. Temperature, flow rate and discharge amount were recorded experimentally at 2, 3 and 4 MPa adsorption pressures, using different activated carbon (AC) as an adsorbent bed. Results show that the central region of the adsorbent bed suffers from the severest temperature fluctuation of the charge and discharge process. It was observed that the best discharged amount was 4 MPa using, G1220 Extra AC as an absorbent bed. Conclusions detected that it is possible mitigate the temperature fluctuations with improved AC properties and the amount of NG desorbed is linearly proportional to the respective tank’s hydraulic volumes.     

Studies on preparation and performances of carbon aerogel electrodes for the application of supercapacitor

Carbon aerogel was prepared by the polycondensation of resorcinol (R) with formaldehyde (F), and sodium carbonate was added as a catalyst (C). Physical properties of carbon aerogel were characterized by infrared spectrometer (IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is found that carbon aerogel is an amorphous material with a pearly network structure, and it consists of one or two diffuse X-ray peaks. The results of cyclic voltammetry indicated that the specific capacitance of a carbon aerogel electrode in 6 M KOH electrolyte was approximately 110.06 F g⁻¹. Through the galvanostatic charge/discharge measurement, it was found that the electrode is stable in KOH electrolyte, the maximum capacitance of the supercapacitor with carbon aerogel as the electrode active material was 28 F g⁻¹. Besides, the supercapacitor has long cycle life. Thus, it was thought that the carbon aerogel is an excellent electrode material for a supercapcitor.     

Supercapacitors based on conducting polymers/nanotubes composites

Three types of electrically conducting polymers (ECPs), i.e. polyaniline (PANI), polypyrrole (PPy) and poly-(3,4-ethylenedioxythiophene) (PEDOT) have been tested as supercapacitor electrode materials in the form of composites with multiwalled carbon nanotubes (CNTs). The energy storage in such a type of composite combines an electrostatic attraction as well as quick faradaic processes called pseudo-capacitance. It has been shown that carbon nanotubes play the role of a perfect backbone for a homogenous distribution of ECP in the composite. It is well known that pure conducting polymers are mechanically weak, hence, the carbon nanotubes preserve the ECP active material from mechanical changes (shrinkage and breaking) during long cycling. Apart of excellent conducting and mechanical properties, the presence of nanotubes improves also the charge transfer that enables a high charge/discharge rate. For an optimal use of ECPs in electrochemical capacitors, a special electrode composition with ca. 20 wt.% of CNTs and a careful selection of the potential range is necessary. The capacitance values ranging from 100 to 330 F g⁻¹ could be reached for different asymmetric configurations with a capacitor voltage from 0.6 to 1.8 V. It is also noteworthy that such a type of ECP/CNTs composite does not need any binding substance that is an important practical advantage.     

Effects of surface treatments of MlNi4.0Co0.6Al0.4 hydrogen storage alloy on the activation,charge/discharge cycle and degradation of Ni/MH batteries

The effects of the surface treatment of the hydrogen storage alloy on the activation property and cycle life of nickel/metal-hydride (Ni/MH) batteries were investigated by means of the electrochemical impedance spectra. It was found that the oxide layer on the alloy surface affected its electrochemical properties and catalysis for the oxygen combination. Therefore, Ni/MH battery employed the untreated alloy as negative electrode material exhibited bad activation property, short cycle life and high internal pressure. Because of the improvement in the metal hydride electrode electrochemical characteristics and catalysis for oxygen recombination by the surface treatment of the alloy in 0.02 M KBH₄+6 M KOH or 6 M KOH solution, the battery used the treated alloy as negative exhibited good activation, long cycle life and low internal pressure. The composition and dissolution of the alloy surface were analyzed by an electron probe microanalysis (EPMA) and induced coupled plasma spectroscopy (ICP). It was found that the Ni-rich surface layer was an important factor to improve the activation and cycle life of battery.     

A high energy density lithium/sulfur–oxygen hybrid battery

In this paper we introduce a lithium/sulfur–oxygen (Li/S–O₂) hybrid cell that is able to operate either in an air or in an environment without air. In the cell, the cathode is a sulfur–carbon composite electrode containing appropriate amount of sulfur. In the air, the cathode first functions as an air electrode that catalyzes the reduction of oxygen into lithium peroxide (Li₂O₂). Upon the end of oxygen reduction, sulfur starts to discharge like a normal Li/S cell. In the absence of oxygen or air, sulfur alone serves as the active cathode material. That is, sulfur is first reduced to form a soluble polysulfide (Li₂S_x, x ≥ 4) that subsequently discharges into Li₂S through a series of disproportionations and reductions. In general, the Li/S–O₂ hybrid cell presents two distinct discharge voltage plateaus, i.e., one at ～2.7 V attributing to the reduction of oxygen and the other one at ～2.3 V attributing to the reduction of sulfur. Since the final discharge products of oxygen and sulfur are insoluble in the organic electrolyte, it is shown that the overall specific capacity of Li/S–O₂ hybrid cell is determined by the carbon composite electrode, and that the specific capacity varies with the discharge current rate and electrode composition. In this work, we show that a composite electrode composed by weight of 70% M-30 activated carbon, 22% sulfur and 8% polytetrafluoroethylene (PTFE) has a specific capacity of 857 mAh g^?1 vs. M-30 activated carbon at 0.2 mA cm^?2 in comparison with 650 mAh g^?1 of the control electrode consisting of 92% M-30 and 8% PTFE. In addition, the self-discharge of the Li/S–O₂ hybrid cell is expected to be substantially lower when compared with the Li/S cell since oxygen can easily oxidize the soluble polysulfide into insoluble sulfur.