High Cathodic Potentials Research Articles

A Study of Particle Size Effect on the Voltage Behavior of LixNi0.5Mn1.5O4 Electrode

Lithium nickel manganese oxide (LNMO, LixNi0.5Mn1.5O4) is an attractive high potential cathode material for rechargeable lithium ion batteries to meet toady’s pressing need of high energy density. One of the main issues faced by LNMO electrode is that its voltage could be invariant with state of charge in charge and discharge operations of battery. This is believed to be originated from its two consecutive phase transition processes during cycling. In this study, a mathematical model is developed to understand the voltage behavior of LNMO electrode in the charge and discharge process by coupling phase transition process with lithium transport process. Effect of electrode particle size on the phase distribution and stability is simulated by the developed model. Results indicate that the voltage behavior of electrode in the charge and discharge can be significantly influenced by different LNMO particle size. Further, electrode with mixed size particles is also investigated by the developed model. Through comparison, limitations of current existing models on predicting LNMO electrode voltage behavior as well as their underlying reasons are discussed based on the modeling results.

Direct synthesis of homogeneous Li2CoSiO4/C for enhanced ionic transport properties in Li-ion battery

Lithium metal orthosilicates are attracting a lot of attention owing to their potential as high capacity and high energy-density cathode materials for Li-ion batteries. Although a number of studies have been performed on lithium metal silicates, understanding of the structure and electrochemical behaviour of Li2CoSiO4 has remained elusive. Herein, homogeneous nanocrystalline Li2CoSiO4/C composites have been synthesized directly by a sol-gel method using water-soluble silicon compounds. X-ray diffraction (XRD) analysis confirmed that the Li2CoSiO4 was well-crystallized in βI phase with Pbn21 space group. From the high resolution transmission electron microscopy (HRTEM) image, the lattice fringes of {001} and {100} are well-resolved. Selected area electron diffraction (SAED) pattern reveal the highly crystalline nature of Li2CoSiO4 and HRTEM image shows the carbon layer coating on particle surface. The Li2CoSiO4 cathode materials delivered an initial discharge capacity of 112 mAhg−1 at C/10 rate with good cyclic performance. The discharge profile of Li2CoSiO4 shows a plateau at 4.1V, revealing its importance as high potential voltage cathode for high energy-density battery.

Исследование влияния пиридина на показатели электролиза цинка из кислых и нейтральных растворов

The particular importance for the practice of zinc electrolysis is the knowledge of the reasons that affect the performance of this process. Previously published data indicate about the negative effects on the zinc current efficiency, energy consumption, quality of the cathode deposit non-optimal composition of the mixture of surfactant: licorice bone glue, lignosulfonate, flocculants, ekstragentami-2-ethyl-hexyl phosphoric acid (D2EHPA) various car oils, kerosene, white spirit, polyacrylamide. Electrochemical studies were performed using three electrolytes of the following composition: 0.25 M ZnSO4, 0.25 M ZnSO4 + 48 g/l H2SO4; 0.25 M ZnSO4 + 18 g/l H2SO4. Potentiostatic and galvanostatic studies were carried out on the potentiostat "Potentiostat P-30J com" by "Elins" using a three-electrode cell. The working electrode (cathode) is made of copper with an area of 0.1 cm2; the auxiliary electrode (anode) is made of a platinum plate with an area of 0.20 cm2, the reference electrode is silver chloride (AgCl/Ag). Measurements were carried out at room temperature under intensive stirring with a magnetic stirrer. Initially, before the removal of the experimental curves, zinc buildup at the cathode was carried out at a constant potential of -1200 mV (AgCl/Ag) for 5 min, using an electrolyte of 0.25 M ZnSO4. For potentiometric measurements, the results are presented by averaged data obtained for 30 seconds of electrolysis, and for galvanostatic measurements by 0.05 seconds from the beginning of electrolysis. In this article, we consider the effect of pyridine additives on the discharge of cations from zinc sulfate electrolytes, including sulfuric acid. The ratio in one of the three electrolytes of zinc mass to the mass of sulfuric acid corresponded to the composition of industrial solutions directed to the electrolysis of zinc. It is shown that the increase in the content of acid in the electrolyte, the increase in the cathode potential and the discharge rate of cations increases with the addition of pyridine decreases. The increase in the discharge rate of cations at low pyridine additives of 0.1 mg/l for electrolytes of the composition: 0.25 M ZnSO4 and 0.25 M ZnSO4 + 18 g/l H2SO4, and the decrease in discharge currents with the addition of 0.6 mg/l pyridine in the electrolysis of a solution containing 18 g/l H2SO4, compared with electrolysis without additives, testified to the priority effect of pyridine on the discharge of hydrogen cations. In the work it is noted, when removing dependencies with pyridine additives at the final stage, an accelerated increase in overvoltage occurs, and without the addition, the increase slows down. This is explained by the fact that the addition of pyridine, due to its ability to protonation and absorption of a significant amount of hydrogen, slows down the discharge of hydrogen to a greater extent than zinc in areas of high current density. It is shown that the final parts of the curves of the voltammograms, the current sharing at high cathodic potentials increased almost nine-fold when the concentration of the pyridine up to 0.3 mg/l However, when the concentration of the pyridine up to 0.6 mg/l current sharing (i_o), as well as the rate of discharge of ions decreases, which is consistent with the equation of Butler-Folmer for the cathodic process at high voltages. The calculation of transport numbers has allowed concluding that at low transport numbers associated with the addition of pyridine, the function of the transition state Gibbs will increase, and the cation will be slower to approach the electrode because of the increased overvoltage. In this case, it is believed that the recovery reaction proceeds in the non-activation mode.

Locally Concentrated LiPF6 in a Carbonate-Based Electrolyte with Fluoroethylene Carbonate as a Diluent for Anode-Free Lithium Metal Batteries.

Currently, concentrated electrolyte solutions are attracting special attention because of their unique characteristics such as unusually improved oxidative stability on both the cathode and anode sides, the absence of free solvent, the presence of more anion content, and the improved availability of Li+ ions. Most of the concentrated electrolytes reported are lithium bis(fluorosulfonyl)imide (LiFSI) salt with ether-based solvents because of the high solubility of salts in ether-based solvents. However, their poor anti-oxidation capability hindered their application especially with high potential cathode materials (>4.0 V). In addition, the salt is very costly, so it is not feasible from the cost analysis point of view. Therefore, here we report a locally concentrated electrolyte, 2 M LiPF6, in ethylene carbonate/diethyl carbonate (1:1 v/v ratio) diluted with fluoroethylene carbonate (FEC), which is stable within a wide potential range (2.5-4.5 V). It shows significant improvement in cycling stability of lithium with an average Coulombic efficiency (ACE) of ∼98% and small voltage hysteresis (∼30 mV) with a current density of 0.2 mA/cm2 for over 1066 h in Li||Cu cells. Furthermore, we ascertained the compatibility of the electrolyte for anode-free Li-metal batteries (AFLMBs) using Cu||LiNi1/3Mn1/3Co1/3O2 (NMC, ∼2 mA h/cm2) with a current density of 0.2 mA/cm2. It shows stable cyclic performance with ACE of 97.8 and 40% retention capacity at the 50th cycle, which is the best result reported for carbonate-based solvents with AFLMBs. However, the commercial carbonate-based electrolyte has <90% ACE and even cannot proceed more than 15 cycles with retention capacity >40%. The enhanced cycle life and well retained in capacity of the locally concentrated electrolyte is mainly because of the synergetic effect of FEC as the diluent to increase the ionic conductivity and form stable anion-derived solid electrolyte interphase. The locally concentrated electrolyte also shows high robustness to the effect of upper limit cutoff voltage.

Mechanistic insights for the electro-Fenton regeneration of carbon materials saturated with methyl orange: Dominance of electrodesorption.

Adsorption followed by regeneration of the adsorbent is a sustainable way to remove pollutants from water systems. In this study, the electro-Fenton regeneration of activated carbon and mesoporous carbon loaded with magnetic γ-Fe2O3 and then saturated with an anionic adsorbate, methyl orange, has been studied. The saturated adsorbents were regenerated and the influence of several factors on the regeneration efficiency and pore structure recovery was systematically investigated. Regeneration was improved with a higher cathodic potential, better contact with the cathode, and larger pores. The addition of an electrochemical potential improved the regeneration of adsorption sites within micropores. A mathematical model based on electrostatic, solvation, and dispersion interaction energies was developed to explain the regeneration process. Cationic (methylene blue) and neutral (benzoic acid) adsorbates were also tested to further test the model predictions. Overall, the results support electro-desorption being the dominant pathway during electro-Fenton regeneration of the carbon materials, with cathodic reduction and electro-Fenton oxidation contributing a minor part to the regeneration via degradation of the desorbed methyl orange.

Zr2N2O Coating-Improved Corrosion Resistance for the Anodic Dissolution Induced by Cathodic Transient Potential.

Developing a corrosion-resistant and electrically conductive coating on metallic bipolar plates is essential to mitigate the performance degradation induced by the high cathodic transient potentials (CTPs) in the start-up/shut-down (SU/SD) processes of polymer electrolyte membrane fuel cells (PEMFCs). Herein, a zirconium oxynitride (Zr2N2O) coating prepared by atomic layer deposition was used to improve the corrosion resistance of 304 stainless steel (304 SS) toward anodic dissolution at various CTPs. Triangular potential pulses were applied to the specimens to simulate potential variations at the cathode side of the PEMFCs at SU/SD stages. Results show that the Zr2N2O coating can provide effective protection at a CTP as positive as 1.1 V versus Ag/AgCl. At all CTPs examined, the peak current density ( ipeak) extracted from the pulse test of the coated specimen (Zr2N2O/SS) is 2 orders of magnitude lower than that of uncoated 304 SS, indicating that the presence of the Zr2N2O coating remarkably increases the corrosion resistance for the anodic dissolution induced by CTPs. More importantly, upon increasing the CTPs, 304 SS experiences severe intergranular corrosion after 4050 pulses, whereas Zr2N2O/SS shows slight pitting corrosion. The quite low ipeak and the mitigated corrosion morphologies of Zr2N2O/SS confirm that incorporating oxygen into the protective coating for achieving a high oxidation resistance is a feasible way to restrain the anodic dissolution caused by high CTPs. Analysis of the electron energy level diagrams of the passive film suggests a protective coating with a wider valence band contributing to the improved corrosion resistance toward the transpassive dissolution.

Cathodically activated Au/TiO2 nanocomposite synthesized by a new facile solvothermal method: An efficient electrocatalyst with Pt-like activity for hydrogen generation

We report here a facile, template-free and one-step solvothermal approach for the synthesis of high-temperature stable gold/titania nanocomposite (NCs), providing a new, simple, quick and inexpensive wet-chemical route. Our approach is based on the assembly of gold salt and titanium butoxide in dimethyl sulfoxide (DMSO). Also, we present here, for the first time, a cathodically activated Au/TiO2 catalyst with Pt/C activity for the hydrogen evolution reaction (HER) in 0.5 M H2SO4 in the dark. The as-prepared (unactivated) Au/TiO2 NCs exhibits considerable electrocatalytic activity for H2 generation in the dark, with a low onset potential (EHER) of −64 mV vs. RHE, a Tafel slope (-bc) of 60 mV dec−1 and an exchange current density (jo) of 0.12 mA cm−2. Long-term stability and durability tests in 0.5 M H2SO4, employing cyclic voltammetry technique (10,000 of repetitive cycling) and 72 h of chronoamperometry measurements at a high cathodic potential (cathodic activation), reveal that the electrocatalyst activates during such aging processes yielding an activated Au/TiO2 catalyst with Pt/C-like activity for H2 generation (EHER -3 mV, -bc: 35 mV dec−1, and jo: 0.95 mA cm−2). The outstanding HER activity of the activated catalyst is discussed.

New insights into the electrochemical behaviour of porous carbon electrodes for supercapacitors

Abstract Activated carbons, with different surface chemistry and porous textures, were used to study the mechanism of electrochemical hydrogen and oxygen evolution in supercapacitor devices. Cellulose precursor materials were activated with different potassium hydroxide (KOH) ratios, and the electrochemical behaviour was studied in 6 M KOH electrolyte. In situ Raman spectra were collected to obtain the structural changes of the activated carbons under severe electrochemical oxidation and reduction conditions, and the obtained data were correlated to the cyclic voltammograms obtained at high anodic and cathodic potentials. Carbon-hydrogen bonds were detected for the materials activated at high KOH ratios, which form reversibly under cathodic conditions. The influence of the specific surface area, narrow microporosity and functional groups in the carbon electrodes on their chemical stability and hydrogen capture mechanism in supercapacitor applications has been revealed.

Operando XAS Studies: Electro-Reduction of CO2 on Nanoporous Cu Foams

New and improved strategies to secure our global energy economy and chemical industry in the future are needed due to the strong dependence on limited fossil resources and the socio-environmental problems associated with increasing anthropogenic emissions of CO2. To counteract this problem and simultaneously to reduce the concentration of the CO2 as well-known greenhouse gas, a very promising route is the electrochemical CO2 reduction reaction (CO2RR) into hydrocarbons and alcohols. Different reaction mechanisms and kinetics for the CO2RR are postulated.[1-4] In particular, the role of Cu oxide during the C2 formation like ethylene and ethanol is poorly understood to date. Further critical issues are addressed: (i) high overpotentials, (ii) broad product distribution, (iii) fast degradation by catalyst poisoning and (iv) competition reaction at high cathodic potentials, referred to as hydrogen evolution reaction. Our work is focusing on the fundamental understanding about the mechanism and kinetics for the CO2RR on nano-porous copper (np-Cu) foams probed by XAS technique. The np-Cu foams prepared by dealloying of Cu-based alloys or by electrodeposition exhibit large surface area-to-volume ratios, improved catalytic performance and high C2 selectivity compared to a flat Cu surface. The catalytic properties (activity and selectivity) can be controlled by the pore size and curvature of the ligaments of the np-Cu. By using operando X-ray absorption spectroscopy (XAS), we studied the various structures and oxidation states of the Cu species in np-Cu foams as function of the applied potential, kind of electrolyte and pH value during the CO2RR. Linear combination fitting and multi-edge EXAFS fit analysis provide us information about the potential-controlled changes of oxidation state and local environment of Cu. In addition, we identified the potential range for the catalyst aging via coarsening and suggest strategies to stabilize the ligament structure and size of the Cu foams during the CO2RR. Based on our operando XAS studies, we obtained a deeper insight to the mechanism and kinetics of the CO2RR on porous Cu foams and clarified the role of Cu oxides for the C2 production. K. P. Kuhl , E. R. Cave, D. N. Abram, and T. F. Jaramillo, Energy Environ. Sci., 5 (2012) p. 7050.A. Dutta, M. Rahaman, N. C. Luedi, M. Mohos, and P. Broekmann, ACS Catal., 6 (2016) p. 2804.H. Mistry, A. S. Varela, C. S. Bonifacio, I. Zegkinoglou, I. Sinev, Y.-W. Choi, K. Kisslinger, E. A. Stach, J. C. Yang, P. Strasser, B. R. Cuenya, Nature Communications, 7 (2016) p. 12123.R. Reske, M. Duca, M. Oezaslan, K. J. P. Schouten, M. T. M. Koper, and P. Strasser, J. Phys. Chem. Lett., 4 (2013) p. 2410.

Highly Concentrated Mg(TFSA)2–MgCl2–Triglyme Electrolytes Toward High Potential Mg Rechargeable Batteries

There is a growing demand for large scale batteries applying to electric vehicles and stationary energy storage systems. Although lithium ion batteries are currently used for these purpose, further innovative batteries in terms of energy density and safety are required. Then, magnesium rechargeable batteries (MRBs) can be a promising candidate because Mg metal has several attractive features, such as its high specific capacity (2205 mAh g- 1), low electrode potential (-2.38 V vs. SHE), and dendrite-free electrodeposition. However, the sluggish Mg diffusion in cathode materials and the limited choice of electrolytes make it difficult to construct full-cell MRBs with high cell voltage. Recently, our group has reported that some spinel oxides (e.g., MgCo2O4) can work as 2–3 V class cathode materials, by utilizing the spinel-to-rocksalt transition with Mg insertion into spinel mother phase [1]. In the previous work, we used a CsTFSA-based ionic liquid as the electrolyte, and the operating temperature was set at 150°C to facilitate Mg diffusion in the spinel oxides. However, Mg metal anode is readily passivated in such electrolytes due to the decomposition of TFSA, which causes a large drop of the cell voltage. Recently, it was reported that the addition of MgCl2 is effective to suppress the passivation of deposited Mg in some ether based solutions of Mg(TFSA)2 [2–4], but the electrolytes that exhibit stable Mg dissolution behavior with a low overpotential as well as high thermal stability at elevated temperatures are not established yet. In this work, we reveal that the Mg deposition/dissolution behavior in the Mg(TFSA)2–MgCl2/Triglyme (G3) solutions can be improved by restricting the amount of G3. Large amounts of MgCl2 salt can be dissolved in highly concentrated Mg(TFSA)2/G3 solutions at elevated temperatures around 150°C, by utilizing the chelating ability of G3 to Mg2+ ions and certain Shrenk-like reactions with Mg(TFSA)2. In particular, as for the mixture of Mg(TFSA)2:MgCl2:G3 = 1:1:2 (molar ratio), where the amounts of Mg and G3 are equimolar, the evaporation of the G3 solvent is efficiently suppressed even at 150°C. In addition, the mixture is crystallized by cooling down to room temperature without any phase separation or recrystallization of MgCl2. The behavior indicates that all G3 molecules coordinate to Mg2+ ions to form equimolar complexes as in the case of the so-called solvate ionic liquids [5], and it is also supported by Raman spectroscopy. More importantly, in the electrochemical measurements at elevated temperatures, the passivation of Mg is markedly suppressed in such highly concentrated solutions, in comparison to in the dilute solutions such as Mg(TFSA)2:MgCl2:G3 = 1:1:10 (molar ratio). In this presentation, we will discuss the solvation structure of Mg2+ ions in the highly concentrated solutions based on the results of Raman spectroscopy and powder-XRD measurements to grasp the origins of the improved Mg deposition/dissolution behavior. To assess the feasibility for MRBs operating at 150°C, battery tests are conducted using full-cells with MgCo2O4 cathodes and Mg metal anodes. We demonstrate that the cell with the electrolyte of Mg(TFSA)2:MgCl2:G3 = 1:1:2 delivers the highest cell voltage of about 2 V during a discharge process among the several electrolytes examined (Figure 1). We will mention how to design electrolytes with high potential cathodes to achieve high performance MRBs.

A Combined Experimental and Theoretical Study on the Activity and Selectivity of the Electrocatalytic Hydrogenation of Aldehydes

A detailed mechanistic study of the electrochemical hydrogenation of aldehydes is presented toward the goal of identifying how organic molecules in solution behave at the interface with charged surfaces and what is the best manner to convert them. Specifically, this study focuses on designing an electrocatalytic route for ambient-temperature postpyrolysis treatment of bio-oil. Aldehyde reductions are needed to convert biomass into fuels or chemicals. A combined experimental and computational approach is taken toward catalyst design to provide testable hypotheses regarding catalyst composition, activity, and selectivity. Electrochemical hydrogenation mechanisms for benzaldehyde and pentanal reduction are found to proceed by a coupled proton–electron transfer process. Initial results show that Au, Ag, Cu, and C catalysts exhibit the highest conversion to alcohol products. These catalysts are suitable because they show high cathodic onset potentials for H2 formation and low cathodic onset potentials for orga...

Towards high-voltage Li-ion batteries: Reversible cycling of graphite anodes and Li-ion batteries in adiponitrile-based electrolytes

Due to their low vapor pressure and their promising electrochemical and thermal stability, NC- (CH2)n-CN dinitriles are proposed as an electrolyte solvent for Li-ion batteries. Adiponitrile (ADN) has substantial advantages, especially for applications requiring high potential cathodes, because it has high electrochemical/thermal stability (up to 6 V vs. Li/Li+,> 120 °C). However, to obtain very high voltage batteries, ADN electrolytes must also passivate the anode of the battery. In this work, reversible cycling of graphite in adiponitrile was successfully achieved by adding a few percent of fluoroethylene carbonate allowing the realization of Graphite/NMC Li-ion battery. The battery of specific capacity of 135 mAhh.g−1 showed a cycling stability for more than 40 cycles. The composition of the solid electrolyte interphase (SEI) was determined as a function of the FEC concentration as well as the state of charge of the graphite anode using hard X-ray photoelectron spectroscopy (HAXPES) and XPS. With FEC, the SEI layer is thinner and depends on the SOC of the anode, but does not depend on the FEC concentration. SEM characterizations clearly showed that the surface of the anode is completely covered by the SEI layer, regardless of the concentration of FEC. Indeed, 2% of FEC is sufficient to suppress the reduction of adiponitrile which is explained by a specific adsorption of FEC on the graphite anode.

A Computational Mechanistic Investigation into Reduction of Gold(III) Complexes by Amino Acid Glycine: A New Variant for Amine Oxidation.

Density functional theory (DFT) was utilized to explore the reduction of gold(III) complexes by the amino acid glycine (Gly). Interestingly, when the nitrogen atom of Gly coordinates to the gold(III) center, its Cα -hydrogen atom becomes so acidic that it can be easily deprotonated by a mild base like water. The deprotonation converts the amino acid into a potent reductant by which gold(III) is reduced to gold(I) with a moderate activation energy. To our knowledge, this is the first contribution suggesting that primary amines are oxidized to imines via direct α-carbon deprotonation. This finding may provide new insights into the mechanistic interpretation of amine oxidations catalyzed/mediated by a center with high cathodic reduction potential. This work also provides a rationalization behind why gold(III) complexes with amine-based polydentate ligands are reluctant to undergo a redox process. Gold(III) reduction occurs most efficiently if the Cα proton leaves in the plane of the Cα , N and Au atoms. Chelation prevents this alignment, resulting in the gold(III) complex being unreactive toward reduction. It has been experimentally found that gold(III) is capable of oxidizing Gly to glyoxylic acid (GA) as the initial product. The latter, in the presence of another gold(III) complex, has been reported to undergo oxidative decarboxylation to afford CO2 and HCOOH. This process is found to be mediated by formation of a geminal diol intermediate produced by reaction of water with the aldehyde functional group of the coordinated GA.

Influence of backscattered neutrals on the grain size of magnetron-sputtered TaN thin films

A side effect of magnetron sputtering is the production of neutral working gas atoms backscattered from the cathode. Their influence on the morphology of sputter-deposited thin films, though, is usually neglected, which may not always be justified. In particular, for high-power impulse magnetron sputtering with its high negative cathode potential during the discharge pulse in combination with heavy metal targets, this effect can be important. In this work, we find experimentally that the grain size of magnetron-sputtered δ-TaN films is considerably reduced at high negative cathode potential and without the use of a substrate bias. For these deposition conditions, computer calculations show a high rate of backscattered neutrals with energies >100 eV, which is only a factor of 10 to 20 lower than the total deposition rate of sputtered species. Such a significant fraction of energetic backscattered neutrals can readily impede grain growth by the incorporation of defects followed by renucleation. Thermalization of the energetic neutrals by the process gas is shown to be insufficient for typical magnetron operating pressures and cathode-substrate distances. The methodology presented here can be used to explain similar results of shrinking grains with increased negative cathode potential for other material systems.

Dominant role of orbital splitting in determining cathode potential in O3 NaTMO2 compounds

Designing high potential cathodes for Na-ion batteries, which are comparable in performance to Li-ion cathodes, remains a challenging task. Through comprehensive density functional calculations, we disentangle the relationship between the cathode potential and the ionicity of $TM-O$ bonds in $O3$ $NaTMO_2$ compounds in which TM ions is a fourth- or fifth-row transition metal. We demonstrate that the magnetic exchange interaction and the local distortions in the coordination environment of TM ions play more significant roles in determining the cathode potential of the $TM^{3+}$ $\to$ $TM^{4+}+ e^-$ reaction than the ionicity of the $TM-O$ bonds in these compounds. These results indicate that designing cathode materials solely based on empirical electronegativity values to achieve high potential may not be a feasible strategy without taking into account a detailed structural assessment.

An electrolyte to improve the deep charge–discharge performance of LiNi0.8Co0.15Al0.05O2 cathode

The electrochemical behaviors of electrolytes, 1 M lithium difluoro(oxalate)borate (LiODFB) in sulfone and dimethyl carbonate blends, have been investigated for LiNi0.8Co0.15Al0.05O2 (NCA) cathode. The viscosity and conductivity tests have been used to investigate the relationship among the solution viscosity, conductivity and electrolyte composition. Through linear sweep voltammetry, cyclic voltammetry, AC impedance and charge–discharge test, we have compared the electrochemical stability of different electrolytes, the reversibility, capacity, cycling performance, rate capability and interfacial impedance of NCA cathode in different electrolytes. SEM, XPS, TEM and FTIR analyses have utilized to discuss the surface nature of NCA cathode after cycles at deep charge–discharge voltage. These results demonstrate that 1 M LiODFB/(SL–DMC, 4:6) electrolyte shows the maximum conductivity value (κmax = 4.25 S cm−1), proper viscosity (η = 3.43 mPa s) and high oxidative decomposition potential (5.66 V) and NCA cathode can present superior reversibility, higher columbic efficiency during cycles in this electrolyte than in 1 M LiPF6/(EC–DMC, 3:7) electrolyte. Besides, a dense deposition layer is formed on the NCA cathode when NCA/Li cells cycle in 1 M LiODFB/(SL–DMC, 4:6) electrolyte with deep charging and discharging process, which can avoid the erosion of electrolyte to transition-metal elements, restrain the damage of NCA structure, and then improves the cycle performance of NCA/Li cells.

Plasma Nitriding of AISI 304 Stainless Steel in Cathodic and Floating Electric Potential: Influence on Morphology, Chemical Characteristics and Tribological Behavior

In direct current plasma nitriding (DCPN), the treated components are subjected to a high cathodic potential, which brings several inherent shortcomings, e.g., damage by arcing and the edging effect. In active screen plasma nitriding (ASPN) processes, the cathodic potential is applied to a metal screen that surrounds the workload, and the component to be treated is placed in a floating potential. Such an electrical configuration allows plasma to be formed on the metal screen surface rather than on the component surface; thus, the shortcomings of the DCPN are eliminated. In this work, the nitrided experiments were performed using a plasma nitriding unit. Two groups of samples were placed on the table in the cathodic and the floating potential, corresponding to the DCPN and ASPN, respectively. The floating samples and table were surrounded by a steel screen. The DCPN and ASPN of the AISI 304 stainless steels are investigated as a function of the electric potential. The samples were characterized using scanning electron microscopy with energy-dispersive x-ray spectroscopy, x-ray diffraction, atomic force microscopy and transmission electron microscope. Dry sliding ball-on-disk wear tests were conducted on the untreated substrate, DCPN and ASPN samples. The results reveal that all nitrided samples successfully produced similar nitrogen-supersaturated S phase layers on their surfaces. This finding also shows the strong impact of the electric potential of the nitriding process on the morphology, chemical characteristics, hardness and tribological behavior of the DCPN and ASPN samples.

First-principles study of mixed eldfellite compounds [formula omitted] (x=0–2, M = Mn, Co, Ni): A new family of high electrode potential cathodes for the sodium-ion battery

Natural abundance of sodium and its similar behavior to lithium triggered recent extensive studies of cost-effective sodium-ion batteries (SIBs) for large-scale energy storage systems. A challenge is to develop electrode materials with a high electrode potential, specific capacity and a good rate capability. In this work we propose mixed eldfellite compounds Nax(Fe1/2M1/2)(SO4)2 (x = 0–2, M = Mn, Co, Ni) as a new family of high electrode potential cathodes of SIBs and present their material properties predicted by first-principles calculations. The structural optimizations show that these materials have significantly small volume expansion rates below 5% upon Na insertion/desertion with negative Na binding energies. Through the electronic structure calculations, we find band insulating properties and hole (and/or electron) polaron hoping as a possible mechanism for the charge transfer. Especially we confirm the high electrode voltages over 4 V with reasonably high specific capacities. We also investigate the sodium ion mobility by estimating plausible diffusion pathways and calculating the corresponding activation barriers, demonstrating the reasonably fast migrations of sodium ions during the operation. Our calculation results indicate that these mixed eldfellite compounds can be suitable materials for high performance SIB cathodes.

Stabilization of Iron-Based Fuel Cell Catalysts by Non-Catalytic Platinum

Since a few years, non-precious metal catalysts with iron or cobalt as active centers show sufficient activity to be viable candidates as electrocatalysts for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFC). They can sustain substantial current densities when operated at low potentials. However, their stabilization at high cathode potentials, necessary for high energy efficiency, remains a daunting task. Here an Fe-N-C catalyst is stabilized over the whole potential range through functionalization with minute amounts of platinum. With the addition of 1 to 2 wt% Pt, the present Pt/Fe-N-C hybrid catalysts show a similar current density at 0.8 V than Fe-N-C but are much more stable during operation in PEMFC. Various characterization techniques, including CO stripping, demonstrate that platinum in these hybrid catalysts is ORR-inactive, not only initially but also after the PEMFC potentiostatic test. It is proposed that the present platinum species protects the Fe-based active sites from the ORR by-product H2O2, or reactive oxygen species produced from its reaction with surface Fe. This proof-of-concept paves the way for a new class of hybrid catalysts, where the activity and stability of Me-N-C catalysts can be independently addressed.

Porous carbon adsorption layer enabling highly reversible redox-reaction of a high potential organic electrode material for sodium ion batteries.

Organic compounds have been utilized in rechargeable batteries as electrode materials on account of their designable structures and reversible redox properties. However, most of them suffer from problems with dissolution resulting in poor electrochemical performance. In this work, we adapt a sodium salt of tetracyanoquinodimethane (NaTCNQ) to work as a high redox potential cathode material in sodium ion batteries (SIBs). A porous carbon coated separator is demonstrated to be an adsorption layer and prevents the dissolved active material from migrating to the anode side. The NaTCNQ cell assembled with a carbon layer containing 5% activated carbon (AC) exhibits a higher initial capacity and greatly improved cycling stability. Using a conductive adsorption layer in organic redox batteries is a promising pathway to develop high performance organic electrode materials for SIBs.