Separate Cathode Research Articles

THE WAYS OF INCREASING WEAR RESISTANCE ABILITY OF WC – Co HARD ALLOY

The paper presents the new knowledge about influence of zirconium as an ingredient of ionic-plasma (Ti, Zr)N coating which was spread on VK10 KS alloy. Ionic-plasma (Ti, Zr)N coating was spread with the use of “Kvant-6” equipment and separate cathodes made from 50 % Ti + 50 % Zr. N2 was used as a reaction gas. In this case two cathodes made from TiN were situated in the chamber of the equipment one against another but the cathode made from ZrN was between them. It was found out that introduction of zirconium into composition of the coating leads to increase of nanohardness as much as 23 % up to 38 500 MPa and Young’s modulus – as much as 67 %, which characterizes the increase of energy of atomic bonds and materials strength. Also it leads to increase of antifriction ability and decrease of friction constant of coating up to μ = 0.07, satisfactory adhesive strength of coating, i.e. generally improves the service features of the whole alloy.

Improving the wear resistance of tungsten-carbide hard alloys

The influence of zirconium in the (Ti, Zr)N ion-plasma coating on VK10KS alloy is studied. The (Ti, Zr)N ion-plasma coating is applied by means of a Kvant-6 instrument, using separate titanium and zirconium cathodes so as to obtain the composition 50% Ti + 50% Zr; nitrogen is used as the reaction gas. In that case, the two titanium-alloy cathodes are opposite one another within the instrument, while the zirconium-alloy cathode is between them. The introduction of zirconium in the (Ti, Zr)N coating increases its nanohardness to 38500 MPa (by 23%) and the Young’s modulus by 67%. That indicates increase in the binding energy of the atoms and the strength of the coating. In addition, we observe increase in wear resistance and decrease in the coating’s frictional coefficient to 0.07, while its adhesive strength is satisfactory. In other words, the performance of the whole hard alloy is improved.

Sea water magnesium fuel cell power supply

An environmentally friendly magnesium fuel cell system using seawater electrolyte and atmospheric oxygen was tested under practical considerations for use as maritime power supply. The hydrogen rate and therefore the power density of the system were increased by a factor of two by using hydrogen evolution cathodes with a gas separation membrane instead of submerged cathodes without gas separation. Commercial magnesium AZ31 rolled sheet anodes can be dissolved in seawater for hydrogen production, down to a thickness below 100 μm thickness, resulting in hydrogen generation efficiency of the anode of over 80%. A practical specific energy/energy density of the alloy of more than 1200 Wh/kg/3000 Wh/l was achieved when coupled to a fuel cell with atmospheric air breathing cathode. The performance of several AZ31 alloy anodes was tested as well as the influence of temperature, electrolyte concentration and anode – cathode separation. The excess hydrogen produced by the magnesium hydrogen evolving cell, due to the negative difference effect, is proportional to the cell current in case of the AZ31 alloys, which simplifies system control considerably. Stable long-term operation of the system was demonstrated at low pressures which can be maintained in an open-seawater-submerged hydrogen generator.

Current transient spectroscopy for trapping analysis on Au-free AlGaN/GaN Schottky barrier diode

This paper presents a combined technique of high voltage off-state stress and current transient measurements to investigate the trapping/de-trapping characteristics of Au-free AlGaN/GaN Schottky barrier diodes. The device features a symmetric three-terminal structure with a central anode contact surrounded by two separate cathodes. Under the diode off-state stress conditions, the two separate cathodes were electrically shorted. The de-trapping dynamics was studied by monitoring the recovery of the two-dimensional electron gas (2DEG) current at different temperatures by applying 0.5 V at cathode 2 while grounding cathode 1. During the recovery, the anode contact acts as a sensor of changes in diode leakage current. This leakage variation was found to be mainly due to the barrier height variation. With this method, the energy level and capture cross section of different traps in the AlGaN/GaN Schottky barrier diode can be extracted. Furthermore, the physical location of different trapping phenomena is indicated by studying the variation of the diode leakage current during the recovery. We have identified two distinct trapping mechanisms: (i) electron trapping at the AlGaN surface in the vicinity of the Schottky contact which results in the leakage reduction (barrier height ϕB increase) together with RON degradation; (ii) the electron trapping in the GaN channel layer which partially depletes the 2DEG. The physical origin of the two different traps is discussed in the text.

Performance Comparison of Three Common Proton Exchange Membranes for Sustainable Bioenergy Production in Microbial Fuel Cell

Proton exchange membranes (PEMs) have essential role in the performance of microbial fuel cells (MFCs). They act as a separator and separate anode and cathode compartments and they also transfer protons between anode and cathode. In this study three types of PEMs (Nafion 112, SPEEK and Nafion 117) have been applied to MFC and the amount of produced bioenergy with the feed of a wastewater in 5000 m/l chemical oxygen demand (COD) have been reported. It has been observed that the MFC working with Nafion 117 as separator produced the highest power among the other MFCs. Also It was found that the produced power was 179.7 mW/m2 for Nafion 117 while it was 126.1 for SPEEK and 19.7 for Nafion 112. Moreover it has been concluded that the low power production of Nafion 112 was due to the diffusion of oxygen from the cathode chamber to the anode chamber that disturb the microorganism's metabolism for degradation of organic compounds. Generally we have found a new economic PEM for using in MFCs.

Preparation of high performance lithium-ion batteries with a separator–cathode assembly

Comparison of the lithium-ion batteries with conventional separator (A) and separator–cathode assembly (B).

New Cathode Materials for the Anion Exchange Membrane Electrolyzer (AEM)

AbstractAn anion exchange membrane electrolyzer (AEM) should combine the positive qualities of the Alkaline Water Electrolysis and the proton exchange membrane (PEM) Electrolysis – compactness, environmentally friendly, effectively and being economically priced. Here, we present improvements of the used substrate materials and of the deposited coatings for developing an AEM with such characteristics. Ni‐wire mesh, stainless steel non‐woven fabrics and stainless steel web were tested as cathode substrate. Base alloys of NiWTiOx, CoNiMoW, CoMn, porous Ni, and porous Ni with TiOx were potentiostatically and galvanostatically deposited. The effect of a single substrate and electrolyte component is graphically shown. We established that, the rougher the structure of an alloy is, the better the electrochemical properties are. The cathode separators were analyzed through EDS‐analysis, light microscopy and REM‐investigations. The electrochemical characterizing was performed galvanostatically in 1 M KOH. The combination substrate‐alloy, which shows the very best electrochemical properties, will be tested in real conditions.

Lithium-Ion Cell Nail Penetration Safety Experiments under Adiabatic Conditions

Nail penetration tests under adiabatic conditions are proposed as a new safety test method to simulate a short circuit caused by intrusion in the worst case scenario, i.e., adiabatic conditions. The behaviors of commercially available 18650 type lithium-ion cells with two different cell chemistries, LiNi0.33Co0.33Mn0.33O2 - LiCoO2 blend (NCM-LCO blend) vs. graphite and LiFePO4 (LFP) vs. graphite, were investigated at different states of charge (SoC). The results show a small standard deviation for the temperature and pressure measurements from five identical experiments. The detailed examination of the nail penetration experiments reveals differences in the safety properties of the cathode materials (LFP vs. NCM-LCO), separator types (PP PE PP trilayer vs. PE single layer) and electrode designs (high power vs. high energy). For both cell types, the observed cooling effect at high energy contents could be linked to an increased gas production due to the loss of electrolyte.

Improved lithium–sulfur batteries with a conductive coating on the separator to prevent the accumulation of inactive S-related species at the cathode–separator interface

Lithium–sulfur (Li–S) batteries are highly attractive for future generations of portable electronics and electric vehicles due to their high energy density and potentially low cost. In the past decades, various novel electrodes and electrolytes have been tested to improve Li–S battery performance. However, these designs on electrodes and electrolytes have not fully addressed the problem of low cycling stability of Li–S batteries. Here, we show the role of the separator in the capacity decay of the Li–S battery, namely that it can accommodate a large amount of polysulfides inside which then precipitates as a thick layer of inactive S-related species. Using a thin conductive coating on the separator to prevent the formation of the inactive S-related species layer, we show that the specific capacity and cycling stability of the Li–S battery are both improved significantly compared to the battery with a pristine separator. Combining this separator design with a monodisperse sulfur nanoparticle cathode, we show Li–S batteries with a life of over 500 cycles with an initial specific capacity of 1350 mA h g−1 at C/2 and a cycle decay as low as 0.09% per cycle.

Systematic Variation of Membrane Chemistry and Biofilm Composition in Strategic Modifications of Microbial Fuel Cells (MFC) and Other Bio-Electrochemical Systems (BES)

Microbial fuel cell (MFC) technology is under development for electricity production for cleansing of waste waters, but also for direct use of the electricity in bio-electrochemical systems (BES) geared to produce high added value products (e.g. acetate and other complex organics from CO2). The presentation will detail systematic examination of the chemical and biological variables in such systems. Both cation and anion exchange membranes of a range of controlled thickness as anode compartment and air cathode separator membrane will be outlined, with the accompanying variations in performance of otherwise similar cells. Both types of membrane can be readily tailored by their production using radiation-induced grafting of appropriately functionalized precursors and subsequent conversion to ionic head groups with accompanying ion-exchange properties.From extensive studies of a range of closely related MFCs, the role of variations in the composition of anode biofilms in operational MFCs have been characterized and compared to the population in suspension [1]. Film composition has been followed using DDGE, identifying the range of microbes present and variations in film composition during operation. Diversity of the community has been found to correlate with cell performance, and hence can be used as a predictor of cell behavior [2].Identification of the make-up of microbial communities in operating MFCs has led to studies of the electrogenic activities of individual strains, and of their interactions when more than one species is present, detecting synergistic or antagonistic relationships. Data on microbial oxidative activity (metabolic profiling) using a range of substrates and a Biolog instrument (multi-well UV-vis spectrometer) have characterized the behaviors of a range of species (e.g. C. denitrificans and B. graminisolvens) not normally considered of significance for power production in MFCs, both as single strains and in combination. “Synthetic communities” derived from these studies are indeed active in production of electricity in MFCs, with product analysis carried out by ion chromatography. A basic outline of the proposed metabolic profile of a synthetic community has been proposed, with individual species being classified as fermentative or electrogenic. The presence of fermentative species may lead to higher power output, contrary to previous orthodoxy. The potential for use of a complex waste (distiller’s dried grains with solubles, DDGS) for production of electricity or in the bio-electrochemical production of high added value products is also under investigation, with useable power densities being achieved Acknowledgements The UK’s SUPERGEN Biological Fuel Cells Consortium (8 univeristies) is led by RS and is funded by Research Councils UK (RCUK) under EPSRC grant EP/H019480/1. Further work in MFC science at Surrey is funded by RCUK under EPSRC grant EP/I004882/1 and BBSRC grant BB/J01916X/1.

The influence of gold nanoparticles on the electroactivity of nickel tetrasulfonated phthalocyanine

We report on the electrodeposition of gold nanoparticles ( AuNPs ) on a glassy carbon electrode (GCE) followed by deposition of nickel tetrasulfonated phthalocyanine ( NiTSPc ) film by electropolymerization (poly- NiTSPc -GCE) to form Poly- NiTSPc / AuNPs -GCE. The presence of the gold nanoparticles caused a lowering of the anodic and cathodic peak separation (ΔEp) of ferricyanide from 126 mV on poly- NiTSPc to 110 mV on poly- NiTSPc / AuNPs . The electrooxidation of nitrite improved on modified electrodes compared to GCE, with the latter giving Ep= 0.78 V and the modified electrodes gave Ep= 0.62 V or 0.61 V. Poly- NiTSPc / AuNPs -GCE had higher currents compared to poly- NiTSPc -GCE. This indicates the enhancement effect caused by the AuNPs . Electrochemical impedance spectroscopy and chronoamperometric studies also showed that poly- NiTSPc / AuNPs -GCE was a better electrocatalyst than poly- NiTSPc -GCE or AuNPs -GCE.

Ion-exchange membrane bioelectrochemical reactor for removal of nitrate in the biological effluent from a coking wastewater treatment plant

Bioelectrochemical reduction of nitrate using an electrode (i.e., cathode) as the electron donor represents a promising method for denitrification; however, this process suffers from the problem of being applied for treating real wastewater, because the cathodic bacteria are susceptible to poisoning by other components in the wastewater. Here we reported the concept of an ion-exchange membrane bioelectrochemical reactor (IEMBER) that integrates the transport of nitrate from a wastewater chamber through an anion-exchange membrane (AEM) with its bioelectrochemical reduction in a separate cathode chamber. Successful removal of nitrate in the biological effluent from a coking wastewater treatment plant was achieved, in good agreement with the obvious cathodic current observed in the IEMBER when its cathode was poised at a potential of −0.50V (vs. SCE). The AEM plays a crucial role in preventing the residuals in the wastewater chamber to enter the cathode chamber, thus avoiding their potential toxicity to the denitrifying bacteria.

A novel process for recycling and resynthesizing LiNi1/3Co1/3Mn1/3O2 from the cathode scraps intended for lithium-ion batteries

To solve the recycling challenge for aqueous binder based lithium-ion batteries (LIBs), a novel process for recycling and resynthesizing LiNi1/3Co1/3Mn1/3O2 from the cathode scraps generated during manufacturing process is proposed in this study. Trifluoroacetic acid (TFA) is employed to separate the cathode material from the aluminum foil. The effects of TFA concentration, liquid/solid (L/S) ratio, reaction temperature and time on the separation efficiencies of the cathode material and aluminum foil are investigated systematically. The cathode material can be separated completely under the optimal experimental condition of 15vol.% TFA solution, L/S ratio of 8.0mLg−1, reacting at 40°C for 180min along with appropriate agitation. LiNi1/3Co1/3Mn1/3O2 is successfully resynthesized from the separated cathode material by solid state reaction method. Several kinds of characterizations are performed to verify the typical properties of the resynthesized LiNi1/3Co1/3Mn1/3O2 powder. Electrochemical tests show that the initial charge and discharge capacities of the resynthesized LiNi1/3Co1/3Mn1/3O2 are 201mAhg−1 and 155.4mAhg−1 (2.8–4.5V, 0.1C), respectively. The discharge capacity remains at 129mAhg−1 even after 30 cycles with a capacity retention ratio of 83.01%.

Tetrahydrofuran hydroperoxide and 3-Aminopropyltrimethoxysilane mediated controlled synthesis of Pd, Pd-Au, Au-Pd nanoparticles: Role of Palladium nanoparticles on the redox electrochemistry of ferrocene monocarboxylic acid

Tetrahydrofuran hydroperoxide (THF-HPO) and 3-aminopropyltrimethoxysilane (3-APTMS) mediated controlled synthesis of palladium (Pd) and palladium-gold bimetallic (Pd-Au) nanoparticles are reported and characterized by TEM, AFM and UV-Vis spectroscopy. A comparative study on the formation of bimetallic nanoparticles via sequential and simultaneous reduction of metal salts is reported. The nanogeometry of as synthesized nanoparticles decreases with an increase in 3-APTMS concentration. The effect of variable nanogeometry of palladium nanoparticles (PdNPs) on the reversible redox electrochemistry of ferrocene monocarboxylic acid (Fc-COOH) is examined with major findings; (1) the homogeneous redox electrochemistry of Fc-COOH tend to become sluggish in the presence of 3-APTMS, (2) the presence of palladium significantly improve the reversible redox behavior of ferrocene derivative with considerable decrease in anodic and cathodic peaks separation, (3) there is an increase in electrocatalytic efficiency during electrochemical sensing of ascorbic acid as a function of nanogeometry and (4) the PdNPs also show admirable peroxidase mimetics activity with remarkable dependence of the same on 3-APTMS concentrations.

Transitions of Ba0.5Sr0.5Co0.8Fe0.2O3-δ and La0.58Sr0.4Co0.2Fe0.8O3-δ

Mixed ionic–electronic conducting perovskites are promising candidates for use as oxygen separation membrane and cathode of solid oxide fuel cells. In the current study, electrical conductivity, magnetic susceptibility, and linear expansion coefficient of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) and La0.58Sr0.4Co0.2Fe0.8O3−δ (LSCF) are measured in a wide temperature range, including room temperature and below. The properties of BSCF reveal a quite complex behaviour, exhibiting five transitions around 200, 350, 500, 800, and 1050K, which can be related to the respective valence state and the spin-state of B-site cations as well as the oxygen non-stoichiometry, whereas those of LSCF has a simple temperature dependence, exhibiting two transitions around 250 and 800K.

A Microscopic Safety Mechanism Study for Li Ion Battery

As the large number of LiB has powering in wide ranges of devices in a variety of usage and environmental conditions, there were several LiB field incidents. Many LiB safety mechanisms studies were devoted to understand the safety hazard and to prevent field safety incidents. Many researches have focused on the inherent safety of the battery materials and on the simulation of the cell abuse conditions. The thermal behavior and stability of the LiB cell and its component were studies by the DSC (Differential Scanning Calorimetry), ARC (Accelerating Rate Calorimeter) and other tools. Many LiB degradation and safety mechanisms were proposed from those results. Meanwhile, some LiB safety standard and approval test are in place to minimize hazard or to prevent field safety incidents, which simulate batteries in the thermal, electrical and mechanical abuse conditions. However frequent LiB field incidents on the certified batteries have still causing big concerns on its safety. Many field incident analysis reports identified that there are important difference between reported LiB safety mechanisms in papers, abuse testing in standards and the real field incidents. And those concluded the battery field incidents almost originated due to the cell internal short circuit that was not predictable at the point of cell manufacturing process and certifciation or approval testing process. There are many factors which can induce cell internal short circuit; -metal impurity in the electrode matrials, -metal particle during cell manufacturing process, -flaw in separator, - flaw in cell design and manufacturing, - defected by electric, mechanical and thermal impact and so on. This paper studied a mechanism of the cell internal short circuit by using microscopic techniques. This technique checks the status of a cell design and manufacturing status of a cell model, which may cause a cell internal short circuit during in use if the cell has flaw. We performed two types o f the "Destructive Physical Analysis" testing to identify a cell's latent possibility of inducing internal short circuit; 1) by measuring the gap between separator and anode and cathode in the jellyroll or cell stacking (sepertor shrinkage allowance at room/high teperatture and cell electrode geometry) by microscopic techniques; 2) by checking the position and status of insulation mechanism in the cell (Electrode tab insulation, Application of insulation, Supplementary Insulation, Internal short avoidance, Position of insulation material). This paper shows the relationship between the status of a cell model and the simulation result of the cell abuse testing (Electric testing, and thermal testing and mechanical testing). This paper identifies the battery safety mechanism which is representing the real field failures and incidents. Attached image file shows relationships between cell design/manufacturing status of a LiB cell and cell abuse simulation testing result.

Multi-Cell Stack of Nonaqueous Lithium-Air Battery

Theoretical energy density of lithium-air battery exceeds 1000 Wh/kg. However, in order to realize such high energy density in practical applications, multiple lithium-air cells must be densely stacked just like in the conventional lithium-ion battery. This requires novel design of the cell stack in which air can be supplied to the cathode. In a fuel cell, gases are supplied to the electrodes through flow channels formed on the bipolar plate. Although this method is also applicable to the lithium-air system, it will result in smaller energy density as well as high cost. Thus, it is extremely important to develop a novel cell stack that provides both high energy density and air supply at a low cost. We have recently developed a multi-cell stack of nonaqueous lithium-air battery and have demonstrated the discharge/charge cycle. Cells were stacked in parallel, similar to the conventional lithium-ion cell stack, but with ~0.5 mm porous current collector between adjacent cathode layers. In this case, air is passively taken up from the periphery of the stack through pores of the current collector. Note that air (oxygen) is naturally breathed in by discharging and breathed out by charging without any additional mechanics like pumps. We believe that such an air-breathing passive system is indispensable to realize both high energy density and low cost. In addition, mass production process for such a cell stack will be quite compatible with the conventional lithium-ion battery. Each cell of the stack is 20 × 20 to 20 × 42.5 mm2 in area and ~0.5 mm thick, and consists of layers of Li metal anode, separator and porous carbon cathode. The porous carbon cathode was prepared by painting Ketjen black paste on a carbon paper. Ether-based electrolytes such as 1 M LiCF3SO3/TEGDME were used. The cell stack assembly and measurements were done in a dry room with the supply-air dew point of −90°C.Figure 1 shows discharge and charge profiles for a two-cell stack with cathode layers inside the stack. Stable discharge at a constant current of 1 mA (current density of ~60 μA/cm2) was observed at ~2.7 V, and lasted for 58 h until the voltage dropped to 2.5 V. The energy density for this stack was roughly estimated to be ~150 Wh/kg although the cell stack design had not been optimized yet. By charging at the same current density, the voltage was gradually increased from ~3 V to over 4 V. These discharge/charge profiles are very similar to those for a single cell, which suggests that air is well breathed in and breathed out from the periphery through the narrow paths between cathode layers. We confirmed that the discharge current density can be increased to 0.5 mA/cm2although the voltage is lowered (2.45 V). Preliminary results for ten-cell stack (~6 mm thick in total) also showed similar cycle profiles.XRD, XANES and FIB-SEM observations showed that Li2O2 was predominantly grown on the carbon cathode during discharge, and decomposed by charging. The observed Li2O2 layer as thick as 200 nm (Fig. 2) strongly suggests that the grown Li2O2 is rather conductive. These results will also be discussed in the presentation.

Generation of Electricity from Sewage

Instead of using energy to treat waste water; it is actually feasible for one to harness energy from wastes as well as treating it using a Microbial Fuel Cell (MFC). An MFC generates electricity from sewage with the help of bacteria. This re- search paper investigates the generation of electricity from sewage as well as sewage treatment in the same period. Four cells were used A, B, C and a control. The cells A, B and C all consisted of the anode and the cathode separated by a loamy-sandy soil of electrical conductivity, 160 � S at 22.8°C. The cathode and anodes were made of carbon rods obtained from A size dry cell. The anode and cathode were separated by 25 mm, 50 mm and 75 mm for cells A, B and C respectively. The control cell had no electrical components but shared the other components as those for cell A, B and C. Sewage with COD of 2080 O2 mg/l was introduced into the cells. Voltage and COD measurements were made every 24 hours and 10 days respectively to investigate performance. Laboratory measurements and recordings were made for 60 days and maximum voltages of 0.426 V, 0.261 V and 0.267 V were recorded for A, B and C respectively. The COD removal efficiencies were over 90 %, for B and C; over 60 % for A and less than 40 % for the control even after 60 days. This asserted that MFCs generated electricity as well as being better waste treatment devices than natural or constructed waste treatment ponds. Results also showed that the further the anode - cathode separation, the lower the voltage that was developed owing to increase in cell internal resistance. This paper furthers the potential to generate green and clean energy by means of an MFC.

Modelling development of acidification within corroding sites on spent fuel surfaces

A model has been developed to predict whether the development of acidity is feasible within actively corroding sites on spent nuclear fuel (UO2) surfaces inside a failed nuclear waste container. The model simulations demonstrate that the build-up of acidity is possible within flaws and pores in a corroded UO2 surface, providing the separation of anodes and cathodes occurs. The extent to which the pH can be depressed is determined by the dissolution rate of the fuel, the dimensions of the defect, the local redox conditions which determine the corrosion potential, and the fraction of the fuel surface that is reactive. Based on the anticipated redox conditions established radiolytically in a failed container it is shown that a suppression of the pH sufficient to accelerate dissolution (pH≤5) is very unlikely.

Effective Separation of Lithium Anode and Sulfur Cathode in Lithium–Sulfur Batteries

AbstractWe demonstrate the importance of effective separation between the sulfur cathode and the lithium anode in Li–S batteries. Improved cycling stability is obtained by using fluoro‐functionalized reduced graphene oxide (rGO) as a separator between the sulfur cathode and the lithium anode. The thickness of the hydrophobic interlayer is found to be 1–2 μm. The possible mechanism is checked with analytical techniques and suggests that improvement in the capacity stability can be attributed to the reduced reactivity of long‐chain polysulfides with the metallic lithium and to the homogenous distribution of end‐discharge products during cycling. The importance of the effective separation of lithium and sulfur is proven by using commercially available lithium conductive ceramics. Good cycling stability over 350 cycles with a coulombic efficiency above 99.95 % is achieved, which demonstrates the possibility of long cycle life with proper separation of lithium and sulfur cathode.