Supercapacitive behavior of mesoporous carbon CMK-3 in calcium nitrate aqueous electrolyte

Calcium nitrate Ca(NO₃)₂ aqueous solution was found to be an effective aqueous electrolyte for a supercapacitor using ordered mesoporous carbon as the electrode materials. The supercapacitive behavior of ordered mesoporous carbon CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte was investigated utilizing cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge measurements. CMK-3 electrode shows excellent supercapacitive behavior with wide voltage window, high specific gravimetric capacitance and satisfactory electrochemical stability in Ca(NO₃)₂ aqueous electrolyte. The specific gravimetric capacitance of CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte reaches 210 F g^?1 at a current density of 1 A g^?1, which is higher than that in conventional aqueous electrolytes NaNO₃ and KOH solution about 40% and 54%, respectively. The high charge density of the electric double layer formed at the interface of the CMK-3 electrode and Ca(NO₃)₂ aqueous electrolyte and the pseudo-capacitive effect originating from the oxygen groups on the surface of CMK-3 were believed to respond for the excellent supercapacitive behavior of CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte.     

“Deactivation of copper electrode” in electrochemical reduction of CO2

Metallic Cu electrode can electrochemically reduce CO₂ to CH₄, C₂H₄ and alcohols with high yields as revealed by the present authors. Many workers reported that formation of CH₄ and C₂H₄ rapidly diminishes during electrolysis of CO₂ reduction. This paper shows that such deactivation of Cu electrode is reproduced with electrolyte solutions prepared from reagents used by these workers. Deactivated Cu electrodes recovered the electrocatalytic activity for CO₂ reduction by anodic polarization at −0.05 V versus she in agreement with the previous reports. Features of the deactivation depend greatly on the individual chemical reagents. Purification of the electrolyte solution by preelectrolysis with a Pt black electrode effectively prevents the deactivation of Cu electrode. Anode stripping voltammetry of Cu electrodes, which were deactivated during electrolysis of CO₂ reduction, showed anodic oxidation peaks at ca. −0.1 or −0.56 V versus she. The severer the deactivation of the Cu electrode was, the higher electric charge of the anodic peak was observed. It is presumed that some impurity heavy metal, originally contained in the electrolyte, is deposited on the Cu electrode during the CO₂ reduction, poisoning the electrocatalytic activity. On the basis of the potential of the anodic peaks, Fe²⁺ and Zn²⁺ are assumed to be the major contaminants, which cause the deactivation of the Cu electrode. Deliberate addition of Fe²⁺ or Zn²⁺ to the electrolyte solutions purified by preelectrolysis exactly reproduced the deactivation of a Cu electrode in CO₂ reduction. The amount of the deposited Fe or Zn on the electrode was below the monolayer coverage. Electrothermal atomic absorption spectrometry (etaas) showed that Fe originally contained in the electrolyte solution is effectively removed by the preelectrolysis of the solution. Mechanistic difference is discussed between Fe and Zn in the deterioration of the electrocatalytic property of Cu electrode in the CO₂ reduction. The concentration of the impurity substances originally contained in the chemical reagents as Fe or Zn is estimated to be far below the standard of the impurity levels guaranteed by the manufacturers. Presence of trimethylamine in the electrolyte solution also severely poisons a Cu electrode in the CO₂ reduction. It was concluded that the deactivation of Cu electrode in CO₂ reduction is not caused by adsorption of the products or the intermediates produced in CO₂ reduction.     

Flow-through electrode for the retention of copper

A flow electrolytic cell is described which uses a vertical porous cathode composed of granulated coke. The cell is applied for the deposition of copper from diluted solutions, 10^?3-10^?2M, in the supporting electrolyte of 0.1 M Na₂SO₄ and 2% per weight H₂SO₄ in water. For the determination of concentration of copper ions in the effluent a radiometric method is applied using the radioactive isotope ⁶⁴Cu. At the applied solution flow rates from 2 to 10 ml min^?1, the coke electrode works efficiently, depositing on a single pass as much as 90% of copper ions present in solution.     

Simple solvothermal synthesis of magnesium cobaltite microflowers as a battery grade material with high electrochemical performances

In this paper, a simple solvothermal method accompanied with a post annealing process was used to synthesize porous and hierarchical MgCo₂O₄ microflowers (MFs), which were composed of many tightly connected nanosheets. The entire synthesis process was accomplished without any surfactant or template participation. The specific surface area of MgCo₂O₄ MFs with mean pore size of 29.6 nm was as high as 71.58 m² g⁻¹. A typical three-electrode system was used to investigate the electrochemical properties of MgCo₂O₄ MFs-based electrode in 2 M of potassium hydroxide aqueous solution as electrolyte. The results demonstrated that such working electrode delivered a specific capacity of 313.3 C g⁻¹ at 1 A g⁻¹, and still remained 189.4 C g⁻¹ even at the current density increasing to 16 A g⁻¹. In addition, the capacity retention reached 74.5% after 5000 cycles at 5 A/g, suggesting its excellent long-term stability. MgCo₂O₄ MFs with highly specific surface area as well as mesoporous microstructures are significantly beneficial to rapid Faradic reaction, in that it ensures sufficient contact of electrolyte/electrode materials and shortens diffusion paths for ions/electrons, as well as maximizes the number of active sites. The synthesis procedure of MgCo₂O₄ MFs proposed in this work is simple and cheap, and is expected to be employed for the preparation of other binary metal cobaltite as well.     

Improved gas diffusion electrodes for hybrid polymer electrolyte fuel cells

In this study, the performance of the anionic electrodes for hybrid polymer electrolyte fuel cells was improved. The anion exchange membrane (AEM) electrodes were initially characterized as the cathode on a proton exchange membrane (PEM) anode/membrane half-assembly (i.e. hybrid polymer electrolyte fuel cell). The electrode performance was improved by tailoring the ionomer distribution within the electrode structure so as to better balance the electronic, ionic, and reactant transport within the catalyst layer. An ionomer impregnation method was used to achieve a non-uniform ionomer distribution and higher performance. Traditional electrode fabrication methods (i.e. thin-film method) lead to a uniform ionomer distribution. The peak power density at 70 °C for a H₂/O₂ hybrid fuel cell was 44 mW cm⁻² using the thin-film electrode, and 120 mW cm⁻² using the ionomer impregnated electrode. A hydrophobic additive used in the catalyst layer further improved the electrode performance, giving a peak power density of 315 mW cm⁻² for H₂/O₂ at 70 °C. Electrochemical impedance spectroscopy was used as an in situ diagnostic tool to help understand the origin of the electrode improvements. The increase in performance was attributed to improved catalyst utilization due to the creation of facile gas transport domains in the AEM electrode structure. Similarly, the AEM anode prepared by ionomer impregnation with polytetrafluoroethylene resulted in a three-fold increase in the peak power density compared to ones made by the thin-film method, which has no polytetrafluoroethylene.     

Decorating carbon nanosheets with copper oxide nanoparticles for boosting the electrochemical performance of symmetric coin cell supercapacitor with different electrolytes

The synergetic combination of double-layer capacitor carbon nanosheets and pseudocapacitive CuO particles with enhanced electrochemical properties had been proposed. Herein, CuO/carbon nanosheets electrode material with outstanding electrochemistry performance was successfully synthesized via a low-cost and controllable strategy. Such rational architecture integrates high-conductivity carbon nanosheets with rich-chemical-activity CuO particles. The surface-functional carbon nanosheets serve as a conductive substrate, provide an efficient pathway and accelerate the fast diffusion of electrons. This electrode material depicts high specific capacitance up to 183.9 and 371.1 F g⁻¹ at 1 A g⁻¹ in Na₂SO₄ and KOH electrolyte using three-electrode tests, respectively. Moreover, two symmetric devices using this CuO/carbon nanosheets electrode material were assembled with different electrolytes. The as-fabricated device with KOH electrolyte delivers remarkable energy density of 19.36 W h kg⁻¹ at power density of 355.6 W kg⁻¹ and still maintains 12.06 W h kg⁻¹ at 1750.7 W kg⁻¹. The as-fabricated device with Na₂SO₄ electrolyte achieves the maximum energy density of 12.46 W h kg⁻¹ at 355.6 W kg⁻¹. The capacitance retention rate is maintained at 94.4% after 2000 cycles in the as-fabricated coin cell supercapacitor with Na₂SO₄ electrolyte, showing outstanding long-cycling life. Herein, the strategic integration of CuO particles with two-dimensional functional carbon nanosheets as the electrode material provides superior electrochemical performance for supercapacitors.     

Electrochemical performance of activated carbon-supported vanadomolybdates electrodes for energy conversion

Reinforcing polyoxomolybdates (POMs) into the activated carbon (AC) template engenders a nanohybrid electrode material for high-performance supercapacitor applications. Herein, a first-time novel integration of two polyoxometalates ([PVMo₁₁O₄₀]^4-, [PV₂Mo₁₀O₄₀]^5-) with AC has been demonstrated, and their structural and electrochemical performances were analyzed. AC-VMo₁₁ composite displayed an enhanced capacitance of 450 Fg^-1 with an improved energy density of 59.7 Whkg^-1. Furthermore, the symmetric supercapacitor cell for AC-VMo₁₁ and AC-V₂Mo₁₀ showed high cell capacitances of 38.8 and 20.01 mF, respectively, alongside 99.99% capacitance retention of over 5000 cycles. In addition, the influence of ionic liquid as an electrolyte on AC-V₂Mo₁₀ based supercapacitor cell was investigated in tetrabutylammonium bromide (TBAB) electrolyte solution.     

Metal electrodes bonded on solid polymer electrolyte membranes (SPE)—III. CO oxidation at Au-SPE electrodes

The electrochemical oxidation of CO was examined on the Au-SPE electrode, which gives ca 10² times larger oxidation current than that of a metal Au electrode immersed in an electrolyte solution. The Au-SPE electrode shows the same reaction mechanism as a metal Au electrode but the amount of the poisonous species, linearly adsorbed CO, is several times less. The product of the CO oxidation leaves into the gas phase as CO₂ with a current efficiency of > 90% though the electrode is in contact with 1 M NaOH+0.1 M Na₂CO₃ through the membrane.A model for the reaction zone of the Au-SPE electrode is discussed.     

Stabilisation of lithiated graphite in an electrolyte based on ionic liquids: an electrochemical and scanning electron microscopy study

1-Ethyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide (EMI-TFSI) is shown to reversibly permit lithium intercalation into standard TIMREX^® SFG44 graphite when vinylene carbonate (VC) is used in small amounts as additive. The best performance was obtained when 5% of VC was added to a 1 M solution of LiPF₆ in EMI-TFSI. Intercalation of lithium in the SFG44 graphite host was demonstrated over 100 cycles without noticeable capacity fading. The reversible charge capacity was around 350 mA h g⁻¹ and an only small irreversible capacity loss per cycle could be observed. Li₄Ti₅O₁₂ was used as counter electrode material. Scanning electron microscopy indicates the reduction of the electrolyte without graphite exfoliation in the neat electrolyte and the formation of a passivation film in the case of a VC-containing electrolyte. Other additives that were tested comprise ethylene sulphite and acrylonitrile which show also a positive effect, but a smaller one than vinylene carbonate. LiCoO₂ positive electrodes were cycled in a 1 M solution of LiPF₆ in EMI-TFSI with good charge capacity retention over more than 300 cycles, when Li₄Ti₅O₁₂ was used as counter electrode. The formation of a passivation film is proven on the LiCoO₂-electrodes, when the electrolyte contained VC, but not in the neat ionic liquid. Finally, the stable cycling of a full cell configuration is proven in this electrolyte system. An ammonium-containing ionic liquid (methyltrioctylammonium-bis(trifluoromethylsulfonyl)-imide, MTO-TFSI) is shown to permit the cycling of both, graphite and lithium cobalt oxide when VC is used as additive in small amounts, but at slightly elevated temperatures.     

Determination of hydroquinone using poly(3‐methylthiophene) synthesized electrochemically on pt electrode in methylene chloride

Poly(3‐methylthiophene) (P3MT) film was synthesized by potentiodynamic method on Pt electrode in methylene chloride solution containing 0.10M tetrabuthlammonium perchlorate supporting electrolyte and used for the determination of hydroquinone (HQ) with amperometric I–t method in solution consisting of NaHSO₄/Na₂SO₄ (SBS; pH 2.0). This modified electrode has a lower working potential and good operational stability due to reducing electrode fouling when compared with the direct oxidation of HQ at the bare Pt electrode. Limit of detection, limit of quantification, and the linear response range were found to be 1.32 × 10^?5 mM, 4.41 × 10^?5 mM, and between 4.41 × 10^?5 – 50.0 mM (R² = 0.997), at 0.50 V versus saturated calomel electrode, respectively. HQ determination in complex matrix was checked using real samples to demonstrate the applicability of modified electrode. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40859.     

Potentiometric study of the interaction of Cr and O ions in fused NaCl-2CsCl eutectic

The physical and chemical properties of chromium chlorides have been studied in fused NaCl-2CsCl eutectic at the temperature range 843-1008 K using an electrochemical cell containing a platinum-oxygen electrode with solid electrolyte membrane, which was used as pO²⁻ indicator electrode. The concentration of oxygen ions in the solution was modifying by dropping the calculated amount of BaO. Titration of Cr³⁺ chlorocomplex by O²⁻ ions demonstrated the precipitation of CrOCl and Cr₂O₃. The solubility constants of these compounds were calculated. E-pO²⁻ and three-dimensional E-pO²⁻-T type diagrams, which summarized the properties of chromium species in the melt, were determined.     

Influence of manganese(II), cobalt(II), and nickel(II) additives in electrolyte on performance of graphite anode for lithium-ion batteries

Manganese dissolution into an electrolyte from the spinel LiMn₂O₄ in the lithium-ion cell has been recently investigated. In order to study the influence of the dissolved manganese species on the lithium intercalation/deintercalation into a natural graphite electrode, the electrochemical behavior of graphite was investigated in 1 mol dm⁻³ LiClO₄ electrolyte solution containing a small amount of Mn(II) by the addition of manganese(II) perchlorate. During the charging process, Mn(II) ions were firstly electroreduced on the electrode around 1.0 V versus Li/Li⁺ followed by irreversible decomposition of the electrolyte and lithium intercalation into the graphite. By microscopic observation of the graphite surface, manganese deposition was confirmed after the charge/discharge test. Due to the manganese deposition, the reversible capacity of the graphite electrode was drastically decreased. Furthermore, the cyclability of the anode was degraded with the amount of the manganese additive increasing. We compared these results with those of the cobalt(II) and nickel(II) additives by dissolving the corresponding perchlorates. Furthermore, we discussed the influence in practical cells based on the consideration of electrochemistry of the deposited metals.     

Cathodic polarization characteristics of the oxygen electrodes/stabilized Bi2O3 solid electrolyte interface

A study has been conducted on the effects of electrode materials and electrolyte stabilizers on the kinetics of the oxygen cathodic reaction at the oxygen electrode/stabilized Bi₂O₃ electrolyte interface in the temperature range of 450-700°C under dry N₂+20% O₂ gas mixture. The La_l-xM_xCoO₃ electrodes prepared by the thermal decomposition method employing the ultrasonic technique and the Ag electrodes by the rf magnetron sputtering method were used as the oxygen electrodes. The electrode/electrolyte interface behaviour was investigated by means of dc and ac measurements. The electrolyte polarization or iR drop could be distinguished from the electrode polarization using an ac method and a current interruption method with the aid of a reference electrode.The electrode process is significantly influenced by the nature of the electrode/electrolyte interface. The dc and ac polarization properties for the system of (Bi₂O₃)_0.77(Y₂O₃)_0.23/La_0.5Sr_0.5CoO₃ electrode prepared by the thermal decomposition method using the ultrasonic technique were more favorable than that of the other electrode/electrolyte systems. The impedance results for the La_0.5Sr_0.5CoO₃ electrode system were different from those for the Ag-sputtered electrode system. It can be considered that the differences are due to the interaction condition between an electrode and an electrolyte, ie the electrochemical matching condition.The reaction mechanisms were also investigated. In the La_0.5Sr_0.5CoO₃ electrode system, the diffusion process of O⁻_ad and/or V^{+ +}₀ along and/or through the interface, respectively, and in the Ag electrode system the O⁻₂ migration process along the interface play an important role in determining the reaction kinetics.     

Treatment of Endocrine Disrupting Chemical From Aqueous Solution by Electrocoagulation

The removal of endocrine disrupting chemical (BPA; Bisphenol–A) from aqueous solution was experimentally investigated by electrocoagulation process. The effects of different combinations of aluminum (Al) and iron (Fe) electrode pair, supporting electrolyte type, supporting electrolyte concentration, initial pH and applied current density and initial BPA concentration on the Chemical Oxygen Demand (COD), and energy consumption performances were critically evaluated. The experiment results indicate that Al–Al electrode pair is the most efficient choice of the four electrode pairs. The COD removal efficiency was increased when NaCl was used as the supporting electrolyte instead of Na₂SO₄ and NaNO_3. The optimum supporting electrolyte type and its concentration, initial pH, applied current density and treatment time were found to be NaCl, 0.05 M, pH 7.0, 12 mA cm^?2 and 40 min, respectively. Energy consumption was found to decrease with increase of NaCl concentration while it increases with increasing applied current density. The initial and treated sample was characterized by UV–vis spectroscopy to confirm the treatment efficiency. The sludge formed during electrocoagulation was characterized by XRD and SEM/EDAX analysis.     

Oxidative conversion of CH4 on Ni and Ag electrode-catalysts in molten carbonate fuel cell reactor

A fuel cell system using molten carbonates of potassium and lithium as electrolyte was applied to the oxidative conversion of methane over Ni and Ag electrodes. A possibility of cogeneration of valuable chemicals, like C₂-hydrocarbons, and electricity in such a system was demonstrated. With CO ₃ ^2– ions (oxygen) transported electrochemically, the rate of formation of C₂-hydrocarbons and selectivity for them on the Ag electrode were found to be greater than those with oxygen premixed to the gase phase.     

Comparative study of the solid electrolyte interphase on graphite in full Li-ion battery cells using X-ray photoelectron spectroscopy,secondary ion mass spectrometry,and electron microscopy

Commercial lithium-ion cells with LiMn_1/3Ni_1/3Co_1/3O₂ as the positive electrode, graphite as the negative electrode and a LiPF₆-EC:PC:DEC electrolyte were cycled under several conditions, and the solid electrolyte interphase (SEI) on the graphite electrode was studied. Nuclear magnetic resonance (NMR) spectroscopy confirmed that LiPF₆-EC:PC:DEC electrolyte was used in the cell and the relative volume ratio between solvents was acquired via quantitative NMR. Secondary ion mass spectrometry, X-ray photoelectron spectroscopy, and a dual-beam focused ion beam/scanning electron microscope have been used to characterize the thickness, morphology and chemical composition of complex SEI on graphite anodes. The advantages and limitations of the characterization techniques are discussed and the results compared to provide a more comprehensive analysis of the SEI.     

Nano-sized copper tungstate thin films as positive electrodes for rechargeable Li batteries

Nano-sized CuWO₄ thin films have been fabricated by radio-frequency (R.F.) sputtering deposition, and are used as positive electrode with both LiClO₄ liquid electrolyte and LiPON solid electrolyte in rechargeable lithium batteries. An initial discharge capacity of 192 and 210 mAh/g is obtainable for CuWO₄ film electrode with and without coated LiPON in liquid electrolyte, respectively. An all-solid-state cell with Li/LiPON/CuWO₄ layers shows a high-volume rate capacity of 145 μAh/cm² μm in first discharge, and overcomes the unfavorable electrochemical degradation observed in liquid electrolyte system. A two-step reactive mechanism is investigated by both transmission electron microscopy and selected area electron diffraction techniques. Apart from the extrusion and injection of Cu²⁺/Cu⁰, additional capacity can be achieved by the reversible reactivity of (WO₄)²⁻ framework. The chemical diffusion coefficients of Li intercalation/deintercalation are estimated by cyclic voltammetry. Nano-CuWO₄ thin film is expected to be a promising positive electrode material for high-performance rechargeable thin-film lithium batteries.     

Al/Cl2 battery with slightly acidic NaCl electrolyte. II. Ti-Ti/Ru oxide chlorine cathodes

A new version of the Al/Cl₂ battery previously described was investigated. Instead of a graphite cylinder, a porous titanium plate was used as a chlorine electrode (cathode). The electrolyte used was a moderately acidic aqueous NaCl solution of pH 2 containing small amounts of In³⁺ and Hg²⁺ as additives. The cell had an open-circuit voltage of 2.6 V and delivered a maximum power of 19.8 W at 1.1 V with a Faradiac efficiency of 69%. The power density was 280 mW cm^–2. A module consiting of 4 submodules connected in series, where each submodule contained 4 double-unit cells connected in parallel, had an open-circuit voltage of 10.6 V, a maximum power of 200 W and an energy density of 110 Whl^–1.     

Solution and solid phase electrochemical behaviour of [Os(bpy)3]3[P2W18O62]

[Os(bpy)₃]₃[P₂W₁₈O₆₂] has been synthesised and characterised by elemental analysis, spectroscopic (UV-vis, IR spectroscopy) and electrochemical techniques. In 0.1 M Bu₄NPF₆ DMSO the complex shows a series of redox couples associated with the Os^3+/2+ and bipyridine ligands of the cationic [Os(bpy)₃]²⁺ moiety and the tungsten-oxo framework of the associated Dawson parent heteropolyanion, [P₂W₁₈O₆₂]⁶⁻. At this electrolyte concentration, the Os³⁺ redox form of the complex was seen to adsorb onto the electrode surface. When the electrolyte concentration is lowered to 0.01 M Bu₄NPF₆ in addition to the Os^3+/2+ redox couple, the redox process associated with the [P₂W₁₈O₆₂]^8−/7− couple also exhibited properties indicating surface based processes were present. Electroactive films of the complex were formed on carbon macroelectrodes by the redox switching of the transition metal within the complex. Voltammetric investigations into the film's behaviour in a range of buffer solutions (pH 2.0, 4.5 and 7.0) were performed. The films were found to possess better stability in acidic pH and the same pH dependence for the tungsten-oxo framework of the heteropolyanions as in solution. Solid state electrochemical measurements on mechanically attached microparticles of the complex were performed, with the effect of both the nature and concentration of the aqueous electrolyte on this behaviour being investigated. Upon redox switching between the Os^2+/3+ redox states, there is an associated insertion/expulsion of anions from/to the solution phase. Scanning electron micrographs of these solid state films were attained before and after redox cycling.     

Characterization of poly(vinylidenefluoride-co-hexafluoropropylene)-based polymer electrolyte filled with TiO2 nanoparticles

Nanoscale TiO₂ particle filled poly(vinylidenefluoride-co-hexafluoropropylene) film is characterized by investigating some properties such as surface morphology, thermal and crystalline properties, swelling behavior after absorbing electrolyte solution, chemical and electrochemical stabilities, ionic conductivity, and compatibility with lithium electrode. Decent self-supporting polymer electrolyte film can be obtained at the range of <50 wt% TiO₂. Different optimal TiO₂ contents showing maximum liquid uptake may exist by adopting other electrolyte solution. Room temperature ionic conductivity of the polymer electrolyte placed surely on the region of >10⁻³ S/cm, and thus the film is very applicable to rechargeable lithium batteries. An emphasis is also be paid on that much lower interfacial resistance between the polymer electrolyte and lithium metal electrode can be obtained by the solid-solvent role of nanoscale TiO₂ filler.