Investigation on the electrode process of the Mn(II)/Mn(III) couple in redox flow battery

The Mn(II)/Mn(III) couple has been recognized as a potential anode for redox flow batteries to take the place of the V(IV)/V(V) in all-vanadium redox battery (VRB) and the Br₂/Br⁻ in sodium polysulfide/bromine (PSB) because it has higher standard electrode potential. In this study, the electrochemical behavior of the Mn(II)/Mn(III) couple on carbon felt and spectral pure graphite were investigated by cyclic voltammetry, steady polarization curve, electrochemical impedance spectroscopy, transient potential-step experiment, X-ray diffraction and charge-discharge experiments. Results show that the Mn(III) disproportionation reaction phenomena is obvious on the carbon felt electrode while it is weak on the graphite electrode owing to its fewer active sites. The reaction mechanism on carbon felt was discussed in detail. The reversibility of Mn(II)/Mn(III) is best when the sulfuric acid concentration is 5 M on the graphite electrode. Performance of a RFB employing Mn(II)/Mn(III) couple as anolyte active species and V(III)/V(II) as catholyte ones was evaluated with constant-current charge-discharge tests. The average columbic efficiency is 69.4% and the voltage efficiency is 90.4% at a current density of 20 mA cm⁻². The whole energy efficiency is 62.7% close to that of the all-vanadium battery and the average discharge voltage is about 14% higher than that of an all-vanadium battery. The preliminary exploration shows that the Mn(II)/Mn(III) couple is electrochemically promising for redox flow battery.     

A comparative study of carbon felt and activated carbon based electrodes for sodium polysulfide/bromine redox flow battery

Carbon felt (CF) and activated carbon (AC) based electrodes for sodium polysulfide/bromine redox flow battery (PSB) were prepared and compared with a laboratory scale PSB flow cell in terms of structure and application performances. The structural properties of the two types of electrodes were characterized by filamentary analog and BET analysis, respectively. Catalyst coating, discharge behavior analysis and thermogravimetric analysis-mass spectrometry (TG-MS) were carried out to make out the different dominant factor in the application performances of the two materials. Compared to AC based electrode (ACE), despite of the relatively low surface area, CF demonstrates almost the same application performances, much more gains in electrochemical activity towards negative half-cell reactions by catalyst coating, and more even discharge voltage curve and stable cycling performance. At current density of 40 mA cm⁻², an average energy efficiency of up to 81% over 50 cycles (about 600 h) has been achieved with cobalt coated CF, but with ACE only 64.7% within 16 cycles, which decreases quickly due to the loss of surface area resulted from sulfur depositing. The difference in structure related to mass transport makes the application performances gap between the two types of materials in PSB.     

Analytical solution for the voltage distribution in one-dimensional porous electrode subjected to cyclic voltammetric (CV) conditions

An analytical solution for the voltage distribution in one-dimensional porous electrode subjected to cyclic voltammetric (CV) conditions was developed by considering the resistivity of both electrode and electrolyte. Voltage distribution inside the electrode as a function of dimensionless distance was generated at different electrode phase resistances. The analytical solution of voltage distribution for cyclic voltammetric conditions was employed in deriving the charging currents. Capacitance studies were conducted on carbons derived from catechol-formaldehyde gels prepared at pH conditions of 3, 6, and 7.5 in 30 wt.% H₂SO₄ electrolyte using CV and constant current charge/discharge studies. Charging currents derived from voltage distribution were fitted with experimental anodic part of CV curves and equivalent series resistance (ESR) was generated. Thus, generated ESR values were compared with that obtained using constant current charge-discharge curves. The model fitted resistance values matched closely with resistance values obtained from galvanostatic constant current charge-discharge method.     

Study of the electrochemical hydrogen storage properties of the proton-conductive perovskite-type oxide LaCrO3 as negative electrode for Ni/MH batteries

LaCrO₃ was prepared by glycine combustion method and investigated as negative electrode for Ni/MH batteries. The structures of the as-calcined powder and the 20th charge-discharge cycle sample were characterized by XRD. The electrochemical experimental results demonstrated that the LaCrO₃ electrode showed excellent electrochemical reversibility and considerably high charge-discharge capacity at various temperatures. Except for the charge-discharge cycle at 298 K, the discharge capacities of LaCrO₃ electrode keep steady at 107.1 mA h g⁻¹and 285 mA h g⁻¹ at 313 K and 333 K after 5 cycles, respectively.     

Microstructure and electrochemical properties of electron-beam deposited Sn-Cu thin film anodes for thin film lithium ion batteries

Thin film Sn-Cu anodes with high Cu content were prepared by electron-beam evaporation deposition using Cu substrate as current collector. Annealing, with the condition being determined by DSC, was used to improve the performance of these electrodes. X-ray diffraction (XRD), scanning probe microscopy (SPM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were used to characterize the structure and composition of the Sn-Cu thin film electrodes. Cyclic voltammetry and galvanostatical charge-discharge measurement were carried out to characterize the electrochemical properties of the as-deposited and annealed electrodes. ?-Cu₃Sn intermetallic phase was formed and interface strength between deposited active materials layer and current collector was enhanced by annealing the as-deposited film under suitable condition. The annealed thin film electrode showed good cycleability and had no phase change during cycling. Although large initial capacity loss was found associated with SEI formation due to increase of surface roughness of annealed electrode, a stable discharge capacity near 300 mAh/g with Coulomb efficiency of about 96% was obtained at voltage window of 0.1-2.0 V and a discharge capacity of about 200 mAh/g and Coulomb efficiency of 97% were kept stable up to 30th cycle at a narrower voltage window of 0.2-1.5 V versus Li/Li⁺.     

Study on capacity fade factors of lithium secondary batteries using LiNi0.7Co0.3O2 and graphite-coke hybrid carbon

In our previous work, 10 Wh-class (30650 type) lithium secondary batteries, which were fabricated with LiNi_0.7Co_0.3O₂ positive electrodes and graphite-coke hybrid carbon negative electrodes, showed an excellent cycle performance of 2350 cycles at a 70% state of charge charge-discharge cycle test. However, this cycle performance is insufficient for dispersed energy storage systems, such as home use load leveling systems. In order to clarify the capacity fade factors of the cell, we focused our investigation on the ability discharge capacity of the positive and negative electrodes after 2350 cycles. Although the cell capacity deteriorated to 70% of its initial capacity after 2350 cycles, it was confirmed that the LiNi_0.7Co_0.3O₂ positive electrode and graphite-coke hybrid negative electrode after 2350 cycles still have sufficient ability discharge capacity of 86 and 92% of their initial capacity, respectively. Accompanied by the result for a composition analysis of the positive electrode material by inductively coupled plasma (ICP) spectroscopy and atomic absorption spectrometry (AAS), electrochemical active lithium decreased and the Li_xNi_0.7Co_0.3O₂ positive electrode could be charged-discharged in a narrow range of between x=0.41 and 0.66 in the battery, although it had enough ability discharge capacity that can use between x=0.36 and 0.87. It is predicted that solid electrolyte interface formation by electrolyte decomposition on the carbon negative electrode during the charge-discharge cycle test is a main factor of the decrease of electrochemical active lithium.     

A rechargeable redox battery utilizing ruthenium complexes with non-aqueous organic electrolyte

A new-type redox battery has been developed. Some ruthenium complexes in organic electrolyte solution were utilized as the electrode active materials. A single cell consisting of [Ru(bpy)₃]²⁺ complex in acetonitrile solution had an open circuit voltage of 2.6 V and a discharge current of 5 mA cm^–2 (at a smooth carbon electrode). The characteristics of this type of cell were much influenced by such factors as the diaphragm material and the concentration of the complex. A cell with flowing electrolyte was also constructed and its charge-discharge performance was examined.     

Use of multiple regression analysis to develop equations for predicting Li-Al/iron sulphide cell performance

A multiple regression analysis was conducted to develop predictive equations for the specific energy and specific power of Li-Al/iron sulphide cells over a wide range of cell designs and operating variables. The intent was to make these equations as general as possible such that one set of equations would predict the performance of Li-Al/FeS or Li-Al/FeS₂ cells with bicell (one positive electrode and two facing negative electrodes) or multiplate cell configurations. Data from 33 cells were used in the analysis of specific energy, and 26 cells were used to develop the specific power equation. The calculated specific energy and specific power showed good agreement with the measured values for these cells. In general, the deviation between the calculated and measured values was within ±10%. A check of the predictive capability of these equations also showed good agreement. The specific energy and specific power calculated for 14 cells not used in the regression analysis deviated by ±10% from the measured values. These equations were used to identify the most likely cell designs to meet selected electric-vehicle battery performance goals. These designs were included in an experimental programme for further performance evaluation.Nomenclature A _e limiting electrode area (cm²) - AHREFF coulombic efficiency (%) - b _i constants in multiple regression equation - CCO cell charge cut-off voltage (V) - CF charge factor (1.0 for fully charged cell, 0.5 for cell 50% discharged, 0.05 for cell discharged to a cut-off of 0.9–l.0 V) - DCO cell discharge cut-off voltage (V) - FCCF fully charged correction factor (1.0 for fully charged cell, 0.05 for any state of discharge) - FSLMUL product of FSUBL and MUL (defined below) - FSUBL calculated utilization factor of the limiting electrode (%) - i _c charge current density (A cm^–2) - i _D discharge current density (A cm^–2) - MUL theoretical specific energy factor (W h kg^–1) - NSPTHC negative-to-positive capacity ratio - OCV cell open-circuit voltage (V) - OFFEUT factor related to LiCl composition in electrolyte (%) - PF power factor (W kg^–1) - POSPIN reciprocal of the number of positive electrode plates - PPXCYC product of the number of positive electrode plates in the cell and the number of deep discharge cycles - R ² correlation coefficient - ¯R _c average cell resistance () - SP calculated cell specific power (W kg^–1) - SPECYC calculated cell specific energy (W h kg^–1) - SPEBAS calculated cell specific energy early in life (W h kg^–1) - TEMPR temperature ratio - TSUBCR thickness ratio of counter electrode and electrode separator - VFSNEG volume fraction salt in the negative electrode - VFSPOS volume fraction salt in the positive electrode - VOLT1R discharge voltage factor - VOLT2R charge voltage factor - W cell weight (kg) - X _i independent variables in regression equation - dependent variable in regression equation     

Filtration Characteristics of a Miniature Electrostatic Precipitator

This study investigates the filtration characteristics of a miniature dual saw-like electrodes electrostatic precipitator (ESP). Parameters such as particle size, rate of airflow through the ESP, voltage of charge electrode, and discharge polarity were considered to study their influence on aerosol penetration through the ESP. Polydisperse and monodisperse particles with sizes ranging from 30 nm to 10 w m were used as the challenge aerosols. Experimental results indicated that the aerosol penetration through the ESP decreased (from 96% to 15% for 0.3 w m) as the voltage of the discharge electrode increased (from + 4 kV to +8 kV) at a flow rate of 30 L/min. At a fixed electrode voltage (+8 kV), aerosol penetration increased from 15% to 69% for 0.3 w m particles as the flow rate increased from 30 to 120 L/min. The most penetrating particle size was in the range of 0.25 w m to 0.5 w m depending on the discharge voltage and the flow rate. In general, the most penetrating particle size of the ESP decreased with decreasing discharge voltage or with increasing flow rate. At the same voltage level but opposite polarity, the aerosol penetration through the ESP with negative corona was lower than that with positive corona. The difference in aerosol penetration was a factor of about 2 between the negative and positive coronas for 0.3 w m particles, and this difference was found to be independent of discharge voltage. Regarding energy conservation, use of a negative-polarity ESP was more economical if the same efficiency was required. However, the ozone generated by the ESP with negative polarity was about five times greater than that generated with positive polarity. Therefore when using an ESP as an indoor air cleaner, the search for an optimum balance between ozone production and aerosol collection efficiency should be considered.     

Electrodeposition and lithium storage performance of three-dimensional porous reticular Sn-Ni alloy electrodes

Three-dimensional (3D) porous materials of Sn-Ni alloy with reticular structure were prepared by electroplating using copper foam as current collector. The structure and electrochemical performance of the electroplated 3D porous Sn-Ni alloys were investigated in detail. Experimental results illustrated that the 3D porous Sn-Ni alloy consists of mainly Ni₃Sn₄ phase with a hexagonal structure. Galvonostatic charging/discharging of annealed 3D porous Sn-Ni alloy confirmed its excellent performances: at 50th charge-discharge cycle, the discharge specific capacity is 505 mAh g⁻¹ and the corresponding charge (delithiation) specific capacity is 501 mAh g⁻¹, yielding columbic efficiency as high as 99%. It has revealed that the porous structure of the alloy can restrain the pulverization of electrode in charge/discharge cycles, and accommodate partly the volume expansion and phase transition, resulting in a significant improvement of cycle life of the Sn-Ni electrode.     

Cycling stability of a hybrid activated carbon//poly(3-methylthiophene) supercapacitor with N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid as electrolyte

A long cycle-life, high-voltage supercapacitor featuring an activated carbon//poly(3-methylthiophene) hybrid configuration with N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid, a solvent-free green electrolyte, was developed. The cyclability of a laboratory scale cell with electrode mass loading sized for practical uses was tested at 60 °C over 16,000 galvanostatic charge-discharge cycles at 10 mA cm⁻² in the 1.5 and 3.6 V voltage range. The reported average and maximum specific energy and power, specific capacitance and capacity, equivalent series resistance and coulombic efficiency over cycling demonstrate the long-term viability of this ionic liquid as green electrolyte for high-voltage hybrid supercapacitors.     

Functional metal-porphyrazine derivatives and their polymers, 10. Secondary fuel cells based on oxygen reduction on platinum electrode modified by polymers and metal-phthalocyanines

Secondary fuel cells based on oxygen reduction of platinum electrode modified by polymers and metal-phthalocyanine (Mt = Fe(III), Co(II), Ni(II), and Cu(II)) were studied. The discharge curves for the platinum electrode modified by poly(2-vinylpyridine) (or polystyrene) and Co-phthalocyanine in 30% KOH aqueous solution, for a 30 min charge at 500 μA, followed by a 100 μA discharge showed a stable plateau at about ?0.24 V SCE (Saturated Calomel Electrode). The open circuit voltage (vs. Zn) of the cell was 1.2 V, and the discharge capacity was of 46 A · h/kg. For this battery there was no significant decay in its characteristics after more than 30 charge-discharge cycles. In Mt-phthalocyanines, the values decreased in the order of Co(II) > Fe(III) > > Cu(II) > Ni(II). From a cyclic voltammogram for the electrode modified by the polymer and Co-Pc, the cathodic reactions were discussed.     

Effect on discharge of the heat treatment of graphite fluoride under a hydrogen atmosphere

Thermal decomposition of two types of graphite fluorides (CF) _n and (CF) _n , has been carried out in a hydrogen atmosphere at several temperatures between 100 and 500°C, with the object of improving the initial discharge behaviour of the Li/graphite flouride cell. The main reaction was the C-F bond rupture to form graphite-like carbon around the particle surface. The drop in cell voltage at the beginning of discharge could be minimized, and the polarization during discharge reduced by heat treatment under a hydrogen atmosphere. (CF) _n , heat treated at 400°C for 1 h, yielded a discharge capacity of 730–800 mA h per g of active material, corresponding to the discharge efficiency of 8390% at 25°C, and (C₂F) _n , heat treated at 350°C, for 10h, gave 670 mA h g^–1, corresponding to 91 % at 25°C.     

Investigation of Ir-modified carbon felt as the positive electrode of an all-vanadium redox flow battery

Porous graphite felts have been used as electrode materials for all-vanadium redox flow batteries due to their wide operating potential range, stability as both an anode and a cathode, and availability in high surface area. In this paper, the carbon felt was modified by pyrolysis of Ir reduced from H₂IrCl₆. ac impedance and steady-state polarization measurements showed that the Ir-modified materials have improved activity and lowered overpotential of the desired V(IV)/V(V) redox process. Ir-modification of carbon felt enhanced the electro-conductivity of electrode materials. The Ir-material, when coated on the graphite felt electrode surface, lowered the cell internal resistance. A test cell was assembled with the Ir-modified carbon felt as the activation layer of the positive electrode, the unmodified raw felt as the activation layer of the negative electrode. At an operating current density of 20 mA cm⁻², a voltage efficiency of 87.5% was achieved. The resistance of the cell using Ir-modified felt decreased 25% compared to the cell using non-modified felt.     

应用于氧化还原电池的Fe3＋/Fe2＋电解液研究

以Fe（Ⅲ）/Fe（Ⅱ）为正极电解液的氧化还原电池,用循环伏安、交流阻抗、充放电等方法研究了在硫酸体系中的电化学行为.结果显示,Fe（Ⅲ）/Fe（Ⅱ）反应是准可逆过程,当硫酸的浓度为0.50 mol/L时,峰电流最大,Fe（Ⅱ）扩散系数Dc为2.276×10-6 cm2/s;在0.37 V下的电化学极化阻抗为2.238 Ω/cm2;与锌溶液组成电池,在20 mA/cm2进行循环充放电,充电电压在1.65 ～1.72 V,放电电压在1.11～1.25 V,电流效率为80％～97％,电压效率为65％ ～75％,能持续稳定循环110次.     

A study of the Fe(III)/Fe(II)-triethanolamine complex redox couple for redox flow battery application

The electrochemical behavior of the Fe(III)/Fe(II)-triethanolamine(TEA) complex redox couple in alkaline medium and influence of the concentration of TEA were investigated. A change of the concentration of TEA mainly produces the following two results. (1) With an increase of the concentration of TEA, the solubility of the Fe(III)-TEA can be increased to 0.6 M, and the solubility of the Fe(II)-TEA is up to 0.4 M. (2) In high concentration of TEA with the ratio of TEA to NaOH ranging from 1 to 6, side reaction peaks on the cathodic main reaction of the Fe(III)-TEA complex at low scan rate can be minimized. The electrode process of Fe(III)-TEA/Fe(II)-TEA is electrochemically reversible with higher reaction rate constant than the uncomplexed species. Constant current charge-discharge shows that applying anodic active materials of relatively high concentrations facilitates the improvement of cell performance. The open-circuit voltage of the Fe-TEA/Br₂ cell with the Fe(III)-TEA of 0.4 M, after full charging, is nearly 2.0 V and is about 32% higher than that of the all-vanadium batteries, together with the energy efficiency of approximately 70%. The preliminary exploration shows that the Fe(III)-TEA/Fe(II)-TEA couple is electrochemically promising as negative redox couple for redox flow battery (RFB) application.     

Disordered carbon negative electrode for electrochemical capacitors and high-rate batteries

In order to understand the properties of high-rate capability and cycleability for a disordered carbon negative electrode in LiPF₆/PC based electrolyte solution, the cell performance tests with various rates and depth of discharges (DODs) has been studied by spectroscopic and electrochemical analyses. From the charge-discharge measurements, a surface carbon-edge redox reaction occurring between a carbonyl (C_edgeO) and a lithium alkoxide (C_edge-OLi) that delivers a large capacity was found fast and high cycleability at only shallow DOD (2.0-0.4 V). The limited or shallow charge-discharge cycling utilizing such facile and reversible action of the C_edgeO/C_edge-OLi of the disordered carbon is suited to an application for an negative electrode of asymmetric hybrid capacitors. A deep DOD discharge (2.0-0.0 V) revealed the existence of some complex processes involving a lithium cluster deposition at pores or microvoids as well as a lithium ion intercalation at graphene layers. The cluster deposition at pores was found to be relatively fast and reproducible. The lithium ion intercalation at graphenes and the subsequent cluster deposition at microvoids were found to be slow and degrade the cycleability after 100 cycles because of the accumulation of a thick and low-ion-conductive solid electrolyte interface (SEI) film on surface.     

Sonochemical intercalation synthesis of nano γ-nickel oxyhydroxide: Structure and electrochemical properties

Nano γ-nickel oxyhydroxide (nano γ-NiOOH), intended as a new positive electrode material for alkaline Zn/Ni batteries, was synthesized by a sonochemical intercalation method. Using NaClO as oxidant, 5 M NiCl₂ solution was added dropwise to a concentrated alkaline solution of NaClO + NaOH, which allows all four elementary reactions (precipitation, oxidation, cation exchange, and water molecule intercalation) to proceed simultaneously under low-frequency ultrasonic irradiation. XRD, SAXS, TEM, SEM, AAS, IR, TG, CT (complexometric titration), cyclic voltammetry (CV), and a charge-discharge test of imitative cell have been used to characterize the microstructural characteristics, composition and electrochemical properties of the synthesized material. The results showed that the lattice parameters of nano γ-NiOOH are a = 2.8256 Å and c = 20.7938 Å. The average oxidation state of Ni in the sample is 3.65 as measured by an indirect iodine method. The alkali metallic Na⁺ ions and water molecules have been inserted into sites between NiO₂ layers. The cyclic voltammogram of nano γ-NiOOH exhibited two cathodic peaks and two anodic peaks, which is in accord with the redox reaction between the various phases of Ni(OH)₂ and NiOOH. The charge-discharge test of imitative cells revealed that nano γ-NiOOH exhibited a higher discharge capacity than spherical β-NiOOH.     

Asymmetric electric double layer capacitors using carbon electrodes with different pore size distributions

Asymmetric capacitors composed of carbon electrodes with different pore size distributions (PSD) were constructed in order to study the fundamental relationship between the PSD of positive and negative carbon electrodes and the performance of electric double layer capacitors. The performance of asymmetric capacitors in a non-aqueous electrolyte solution (TEMA·BF₄/PC) was found to be governed by the PSD of the carbon used in the negative electrode. Capacitance depends on the BET surface area of the negative electrode and the rate performance depends on its mesoporous surface area. These results were explained by the fact that it is more difficult to adsorb large solvated cations (TEMA⁺) in micropores (less than 2 nm wide) than in mesopores (2-50 nm wide), and that this is more difficult with a higher rate of charge-discharge.     

Aging of electrochemical double layer capacitors with acetonitrile-based electrolyte at elevated voltages

Laboratory-scale electrochemical capacitor cells with bound activated carbon electrodes and acetonitrile-based electrolyte were aged at various elevated constant cell voltages between 2.75 V and 4.0 V. During the constant voltage tests, the cell capacitance as well as the capacitance and resistance of each electrode was determined. Following each aging experiment, the cells were analyzed by means of electrochemical impedance spectroscopy, and the individual electrodes were characterized by gas adsorption and X-ray photoelectron spectroscopy. At cell voltages above 3.0 V, the positive electrode ages much faster than the negative. Both the capacitance loss and resistance increase of the cell could be totally attributed to the positive electrode. At cell voltages above 3.5 V also the negative electrode aged significantly. X-ray photoelectron spectroscopy indicated the presence of degradation products on the electrode surface with a much thicker layer on the positive electrode. Simultaneously, a significant decrease in electrode porosity could be detected by gas adsorption.