Electrolytic Saturation Research Articles

Boosting Lithium-Ion Storage Capability in CuO Nanosheets via Synergistic Engineering of Defects and Pores.

CuO is a promising anode material for lithium-ion batteries due to its high theoretical capacity, low cost, and non-toxicity. However, its practical application has been plagued by low conductivity and poor cyclability. Herein, we report the facile synthesis of porous defective CuO nanosheets by a simple wet-chemical route paired with controlled annealing. The sample obtained after mild heat treatment (300°C) exhibits an improved crystallinity with low dislocation density and preserved porous structure, manifesting superior Li-ion storage capability with high capacity (~500 mAh/g at 0.2 C), excellent rate (175 mAh/g at 2 C), and cyclability (258 mAh/g after 500 cycles at 0.5 C). The enhanced electrochemical performance can be ascribed to the synergy of porous nanosheet morphology and improved crystallinity: (1) porous morphology endows the material a large contact interface for electrolyte impregnation, enriched active sites for Li-ion uptake/release, more room for accommodation of repeated volume variation during lithiation/de-lithiation. (2) the improved crystallinity with reduced edge dislocations can boost the electrical conduction, reducing polarization during charge/discharge. The proposed strategy based on synergic pore and defect engineering can pave the way for development of advanced metal oxides-based electrodes for (beyond) Li-ion batteries.

Three-Dimensional Interconnected Network Architecture with Homogeneously Dispersed Carbon Nanotubes and Layered MoS2 as a Highly Efficient Cathode Catalyst for Lithium-Oxygen Battery.

The structure and catalytic activity of the oxygen electrode determine the overall electrochemical performance of lithium-oxygen (Li-O2) batteries. Here, a three-dimensional (3D) porous interconnected network structure combined with ultrathin MoS2 nanosheets with homogeneously dispersed CNTs (MoS2/CNTs) was synthesized via a one-step hydrothermal reaction. The 3D interconnected architecture can efficiently promote the diffusion of O2 and Li ions as well as impregnation of electrolyte and provide more abundant storage space for the accommodation of discharge products, while the incorporation of uniformly dispersed CNTs improves the electronic conductivity and maintains the integrity of the cathode structure. Therefore, the Li-O2 battery based on MoS2/CNTs achieves improved performance with the low overpotentials (discharge/charge overpotentials of approximately 0.29 and 1.05 V), a high discharge specific capacity of 6904 mA h g-1 at a rate of 200 mA g-1, and excellent cycling stability (132 cycles). Experimental studies reveal that the improved electrochemical performance can be ascribed to the synergistic advantages of electronic conductive CNTs and excellent catalytic activity of the MoS2 nanosheets. Moreover, the unique 3D interconnected network structure can effectively facilitate fast charge transfer kinetics and a facile mass transport pathway. These encouraging performances demonstrate the metal sulfide catalyst as a promising catalytic material of oxygen electrodes for Li-O2 batteries.

Combined treatment plasma electrolytic carburizing and borocarburizing on Q235 low-carbon steel

The boride layers were fabricated on Q235 low-carbon steel by duplex plasma electrolytic saturation treatment in order to improve the boriding efficiency. The two-step process for plasma electrolytic carburizing (PEC) with 5 min and plasma electrolytic borocarburizing (PEB/C) with 5 min–15 min was applied. Their microstructure, hardness, corrosion and wear behaviors were analyzed. XRD and XPS spectra confirmed that the modified boride layers consisted mainly of Fe2B phase. The thickness of the borided layers for combined PEC + PEB/C treatment increased considerably comparing to PEB/C treatment alone. The PEC pretreatment can enhance the growth of boride layer for the following PEB/C process. The corrosion resistance and wear resistance of Q235 low-carbon steel with combined PEC + PEB/C treatment were also significantly improved. In addition, by increasing the PEB/C time from 5min to 15min, the hardness、corrosion and wear resistance of boride layer on PEC + PEB/C samples increased. The main reason was that the thickness and Fe2B phase content of boride layer increased.

Formation of Plastic Zones near Spherical Cavity in Hardened Low-Carbon Steels under Conditions of Hydrogen Stress Corrosion

A method for mathematical description of local stress condition and formation of plastic zones near spherical pores formed at room temperature in the volume of low-alloy structural steels during their electrolytic hydrogen saturation under stress is proposed. The impact of external tension stress and pressure of gases (hydrogen and methane) in pores is taken into account. The method is promising for specification of kinetic parameters of destruction processes in structural steels under conditions of hydrogen stress corrosion.

CHANGES IN ULTRASONIC VELOCITY AT HYDROGEN EMBRITTLEMENT OF HIGH-CHROMIUM STEEL

The paper presents research into changes in the ultrasonic velocity (Rayleigh wave propagation) at plastic deformation of the type 40Kh13 corrosion-resistant high-chromium steel with a sorbitol structure after high-temperature tempering (original state) and after electrolytic hydrogenation saturation for 12 and 24 h. The method implementation for measuring Rayleigh wave propagation includes a periodic generation of square-waves 100 nm long. Measurements are performed at the input of a radiating piezoelectric transducer including the wave propagation over the specimen using a receiving piezoelectric transducer connected to a digital oscilloscope. Measurements show changes not only in the deformation curve at uniaxial tension but also in the dependence between the ultrasonic velocity and deformation.

(Invited) Multiscale Morphological and Electrical Characterization of Charge Transport and Charge Transfer Limitations to Power Performance of Positive Electrode for Li-Ion Batteries

Composite materials consisting of several interpenetrated and percolating phases are widely used as electrodes for a variety of electrochemical cells. Such electrodes are generally mixed ionic−electronic conductors, in which ions and electrons are confined to transport within the specific conducting network. In particular, for electrochemical storage and energy transformation devices, the transport properties play critical roles in determining their performance, which is pivotal to improve them for service as power sources. To reach this goal, an increased fundamental understanding of the factors that play on the transport properties within such composite materials is still required. The transport of the electrons and ions through Li-ion battery electrode and their transfer to the active matter depend on the electrode architecture (nano- and microstructure) through the interfacial areas, materials connectivity, and the transport length scales. Novel opportunity for progressing in this direction and exploring relationships between electrode architecture, charge transport and electrochemical performance is implementation of X-ray computed tomography (XRCT) and focused ion beam in combination with scanning electron microscopy (FIB-SEM) techniques to characterize and quantify the 3D architecture of composite electrodes. In particular, tortuosity, a critical parameter with respect to ionic transport, has been exhaustively studied. Comparatively, factors that play on the electrons transport and wiring to the active mass have been much less considered. Moreover, attempts to correlate quantified 3D geometries with measured electrochemical power performance or electrical transport properties of same real electrodes remain rare. We intend to fill this gap in this presentation. We have undertaken exhaustive characterizations of 3D geometries of LiNi1/3Mn1/3Co1/3O2 (NMC), LiFePO4 (LFP), and NMC/LFP blended electrodes and rationally interpreted their measured electrical properties and electrochemical performance. A combination of X-Ray tomography and FIB-SEM tomography are used for a multiscale analysis of electrodes 3D geometries, in particular the distribution of the conductive additive and the binder that perform as electronic wires, the tortuous pores distribution, which after electrolyte impregnation perform as ionic wires, and the inter-connectivity between the active matter phase and the electronic and the ionic wires [1]. The electrical properties (permittivity and conductivity) are measured from low (a few Hz) to microwave (a few GHz) frequencies by the broadband dielectric spectroscopy technique [2]. This one is very sensitive to the different scales of the electrode architecture involved in electronic transport, from interatomic distances to macroscopic sizes, as well as to the morphology at these scales, coarse or fine distribution of the constituents [2,3]. In addition to the geometry of the electrode architecture, the interfaces (adsorption of ions to the surface of active material and carbon nanoparticles), and interactions at such interfaces lead to a reciprocal influence of ionic and electronic transfers at the different scales of the electrode [4]. Finally, discharge rate performance is analyzed by simple, yet efficient methods. This approach allows discriminating between the contributions of the electronic and ionic wiring networks as the performance limiting factors, depending on the electrode geometry and discharge rate. [5] Acknowledgements Financial funding from the ANR Program No. ANR-15-CE05-0001-01 (PEPITE) is acknowledged. We also thank the CLYM (Centre Lyonnais de Microscopie) supported by the CNRS, the “Grand Lyon” and the Rhône-Alpes Region for use of the Zeiss NVision40 FIB/SEM. The IMD (Institut de la Mobilité Durable – Sustainable Mobility Institute) is also acknowledged for financial support.

CHARACTERIZATION OF NITROCARBURIZED COATING BY PLASMA ELECTROLYTIC SATURATION

<p class="AMSmaintext">Plasma electrolytic saturation (PES) is an atmospheric pressure plasma deposition which is used for fabrication of nanostructural coatings. This process starts with the appearance of some sparks on the surface and finally by the formation of plasma envelope around the sample, particles and free radicals bombard the surface and diffusion takes place into the work-piece. In this paper, the effect of frequency (500, 1000 and 10000 Hz) as pulse parameters on properties of nitrocarburized layers deposited on AISI 1045 steel were investigated. The analytical characteristics of the coating were assessed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The corrosion behavior of coatings was analyzed by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 3.5% sodium chloride solution. Moreover, the microhardness and wear resistance of coated samples were also studied. The results indicated that applying nitrocarburized layer in all cases, improved the corrosion resistance, microhardness and also wear resistance of the substrate. The coatings treated at the frequency of 10000 Hz, had corrosion resistance about 2.4 and 1.4 times higher than those of the samples prepared at the frequency of 500 Hz and 1000 Hz. The surface hardness of 10000 Hz treated sample was about 1040 Vickers, which was more than those of the two other ones. An increase in frequency also caused wear resistance to increase. </p>

Diffusion of carbon and nitrogen in TC4 titanium alloy plasma electrolytic saturation

The study aims at deriving an equation for the temperature field of the specimen- vapour-gaseous envelope (VGE) – electrolyte three-phase system, followed by the calculation of the temperature distribution expression. The diffusion mechanism of carbon and nitrogen, in light of the theory of molecular diffusion, and the mechanism behind the plasma electrolytic saturation, is also discussed. In the PES process, the diffusion of carbon and nitrogen is affected by the strengthening voltage and processing time, which in turn affects the thickness and element distribution of the diffusion layer. Carbon, of which the diffusion depth ranges from 0.5 μm to 2.5 μm, is mainly distributed into the outermost layer. While the nitrogen is able to distribute throughout the diffusion layer as indicated by its several tens microns of diffusion depth. Further, the influence of process parameters on the diffusion of atoms during the strengthening process is verified experimentally.

3D Foam-Like Composites of Mo2C Nanorods Coated by N-Doped Carbon: A Novel Self-Standing and Binder-Free O2 Electrode for Li-O2 Batteries.

The development of self-standing and binder-free O2 electrodes is significant for enhancing the total specific energy density and suppressing parasitic reactions for Li-O2 batteries, which is still a formidable challenge thus far. Here, a three-dimensional foam-like composite composed of Mo2C nanorods decorated by different amounts of N-doped carbon (Mo2C-NR@xNC (x = 5, 11, and 16 wt %)) was directly employed as the O2 electrode without applications of any binders and current collectors. Mo2C-NR@xNC presents a network microstructure with interconnected macropore and mesoporous channels, which is beneficial to achieving fast Li+ migration and O2 diffusion, facilitating the electrolyte impregnation, and providing enough space for Li2O2 storage. Additionally, the coated N-doped carbon layer can largely improve the electrochemical stability and conductivity of Mo2C. The cell with Mo2C-NR@11NC shows a considerable cyclability of 200 cycles with an overpotential of 0.28 V in the first cycle at a constant current density of 100 mA g-1, a superior reversibility associated with the formation and decomposition of Li2O2 as desired, and a high electrochemical stability. On the basis of the experimental results, the electrochemical mechanism for the cell using Mo2C-NR@11NC is proposed. These results represent a promising process in the development of a self-standing and binder-free foam-based electrode for Li-O2 batteries.

Formation of holes into granule Li4Ti5O12 anode for enhanced performance of hybrid supercapacitors

Hybrid supercapacitors are being studied as a next-generation energy storage device that bridge supercapacitor and lithium-ion battery. However, an imbalance of two electrodes of hybrid supercapacitors, especially due to the slow lithium ion kinetics at anode is the one of the most important problems. To solve this problem, we have demonstrated optimized hybrid supercapacitor performance by applying the punched granule Li4Ti5O12 (P-LTO) via mechanical punching as a high power anode. The hybrid supercapacitors based on P-LTO anode and activated carbon delivers not only high specific capacity of 57 F/g and excellent long-term cycling of 99% after 14,000 cycles but also remarkable rate capability of 90.6% even at a high rate of 4 A/g, mainly due to i) increase in the total effective contact area, ii) efficient electrolyte impregnation and iii) effective dispersion of hydrogen fluoride attack.

Ag-decorated highly mesoporous Co3O4 nanosheets on nickel foam as an efficient free-standing cathode for Li-O2 batteries

Highly mesoporous cobalt oxide nanosheets are grown on nickel foam (M-Co3O4/NF) by a hydrothermal method. Ag nanoparticles with 10–50 nm diameters are uniformly distributed on the surface of the mesoporous Co3O4 nanosheets (Ag/M-Co3O4/NF) after chemical bath reaction. Moreover, we discovered that the homogeneous distribution of Ag nanoparticles on free-standing, highly mesoporous Co3O4 nanosheets showed the synergistic effect of the high electrocatalyst reactions toward the ORR from Ag and OER from M-Co3O4. Highly mesoporous Co3O4 nanosheets with a thickness of 10 nm as free-standing cathode for Li-O2 battery are beneficial to accommodating insoluble discharge products and facilitating oxygen diffusion and electrolyte impregnation. Ag nanoparticles can improve the electrical conductivity of the O2 electrode and provide a catalytic activity for ORR at the same time. The Ag/M-Co3O4/NF exhibited a robust catalytic activity as cathode for Li-O2 batteries with a high reversible capacity of 2471.1 mA h g−1, a low discharge/charge overpotential, and a cycle life of 124 cycles (under the curtaining capacity of 500 mA h g−1). The preliminary results indicate that Ag/M-Co3O4/NF is an efficient and stable bifunctional cathode for Li-O2 batteries.

Carbon-Nanotube-Incorporated Graphene Scroll-Sheet Conjoined Aerogels for Efficient Hydrogen Evolution Reaction

Developing low-cost Pt-free hydrogen evolution reaction (HER) electrocatalyst is highly desired in exploiting hydrogen as a sustainable new energy carrier. Herein, hierarchically structured graphene-carbon nanotube aerogel-MoSe2 hybrid (GCA-MoSe2) was constructed as efficient HER electrocatalysts. GCA was facilely fabricated by direct freeze-drying of graphene oxide (GO)-carbon nanotube (CNT) hybrid dispersion, with subsequent carbonization. Through a shock cooling method, a unique scroll-sheet conjoined architecture could be formed in GCA, which can function as highly conductive skeleton, thus facilitating the transport of electrons through the whole hybrids. Furthermore, CNTs acting as “spacers” between graphene layers can efficiently impede their restacking, thus giving full play to the superior electrical conductivity of graphene. The hierarchical porous aerogel skeleton could allow full impregnation of electrolyte, accelerating the ion diffusion kinetics. Benefiting from the three-dimensional (3D) ne...

Characterization and one-step synthesis of Hydroxyapatite-Ti(C,N)-TiO2 composite coating by cathodic plasma electrolytic saturation and accompanying electrochemical deposition on titanium alloy

Besides oxides ceramic coating, cathodic plasma electrolytic saturation (PES) could produce more other types ceramic coatings, including nitrides, carbonitrides, borides, etc., on nearly all kinds of metal substrate. Owing to the accompanying electrochemical deposition (ED) effect of PES, special functional compounds could be deposited in mentioned ceramic coatings by PES simultaneously in special designed electrolyte. In this study, the target Hydroxyapatite (HA)-Ti(C,N)-TiO2 composite coatings were synthesized in one step by PES and accompanying ED in calcium nitrate and sodium dihydrogen phosphate containing formamide based electrolyte. The phase structures, functional groups of molecules, chemical compositions of the surfaces and binding energies of atoms in coatings were characterized by X-ray diffraction (XRD), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) respectively. The surfaces morphologies, cross sections morphologies, and element maps of the surface were analyzed by Scanning electron microscopy (SEM) and energy dispersive spectrum (EDS). The coatings exhibit porous structure with island like bulges or spheroids around the pores. The phases formed in coatings are verified to be constituted of HA, Ti(C,N) and anatase. The suggested formation mechanism of anatase in coatings differs to that obtained on anodic titanium surface in PEO process. The phase of HA distributes homogenously on surfaces and displays as clusters congressed by nano-scale needles or rods with their transverse length about ~10nm. The size of the pores and bulges, the crystalline amount of HA phase, and the thickness of the coatings all increase with increasing duration time. The thickness reaches about 56±7μm when the duration time grew to 30min, 26% higher than that of the HA-free coating produced in formamide electrolyte with the same process parameters.

Increasing Wear Resistance of Titanium Alloys by Anode Plasma Electrolytic Saturation with Interstitial Elements

In our previous studies, we have shown that anode plasma electrolytic saturation of titanium alloys with nitrogen and carbon can improve their tribological properties. Obtained structure containing oxide layer and solid solution of diffused element in titanium promotes the enhancement of running-in ability and the decrease in the wear rate in some special cases. In this paper, further investigations are reported regarding the tribological properties of alpha- and beta-titanium alloys in wear test against hardened steel (50 HRC) disk using pin-on-disk geometry and balls of Al2O3 (6.25 mm in diameter) or bearing steel (9.6 mm in diameter) with ball-on-plate one and normal load from 5 to 209 N. Reproducible results were obtained under testing samples treated by means of the plasma electrolytic nitriding (PEN) with the mechanical removal of the oxide layer. Friction coefficient of nitrided samples is 0.5-0.9 which is somewhat higher than that for untreated one (0.48-0.75) during dry sliding against Al2O3 ball. An increase in the sliding speed results in the polishing of nitrided samples and reduction of their wear rate by 60 times. This result is obtained for 5 min at 850 °C using PEN in electrolyte containing 5 wt.% ammonia and 10 wt.% ammonium chloride followed by quenching in solution. Optical microscope was employed to assist in the evaluation of the wear behavior. Sizes of wear tracks were measured by profilometer TR200.

Hierarchical Porous Carbon Spheres for High‐Performance Na–O2 Batteries

As a new family member of room-temperature aprotic metal-O2 batteries, Na-O2 batteries, are attracting growing attention because of their relatively high theoretical specific energy and particularly their uncompromised round-trip efficiency. Here, a hierarchical porous carbon sphere (PCS) electrode that has outstanding properties to realize Na-O2 batteries with excellent electrochemical performances is reported. The controlled porosity of the PCS electrode, with macropores formed between PCSs and nanopores inside each PCS, enables effective formation/decomposition of NaO2 by facilitating the electrolyte impregnation and oxygen diffusion to the inner part of the oxygen electrode. In addition, the discharge product of NaO2 is deposited on the surface of individual PCSs with an unusual conformal film-like morphology, which can be more easily decomposed than the commonly observed microsized NaO2 cubes in Na-O2 batteries. A combination of coulometry, X-ray diffraction, and in situ differential electrochemical mass spectrometry provides compelling evidence that the operation of the PCS-based Na-O2 battery is underpinned by the formation and decomposition of NaO2 . This work demonstrates that employing nanostructured carbon materials to control the porosity, pore-size distribution of the oxygen electrodes, and the morphology of the discharged NaO2 is a promising strategy to develop high-performance Na-O2 batteries.

INVESTIGATION OF THE ELECTROLYTE EFFECT ON VN CREATED VIA PES

One of the most important methods of hardening steel tools is nitriding. During this process, nitrogen diffuses into the sample surface at high temperature and reacts with the elements existing in the sample and creates hard nitrides. Another way to create hard nitrides is the simultaneous hard diffusion of two nitride-causing elements. During the plasma electrolytic saturation process, one nitride –causing element, together with nitrogen, diffuses into the surface of the sample and forms a hard nitride coating on the surface of the component. In this process, a voltage is applied between a cathode (sample with smaller surface) and an anode (sample with larger surface); the plasma is formed on the surface of the cathode which then let the given elements diffuse into the surface of the base metal. In the present study, nitrogen and vanadium have diffused into the surface of the sample, 1.2436 tool steel, and vanadium nitride has been formed. The best combination of electrolyte solution is 4g Ferro vanadium, 50±1 ml nitric acid and sodium hydroxide. The results is indicating that the formed coating layer thickness is about 2-3.5 μm. As the conductivity increases, the condition for diffusion is provided; however, with over increasing the temperature, diffusion decreases. The coating formation has observed in 7-10±0.5 A current.

Influence of hydrogen on the localization of plastic strain in low-carbon steel

The localization of plastic strain in the extension of 08ps low-carbon steel is compared after hot rolling and after electrolytic saturation with hydrogen by means of a three-electrode electrochemical cell. Analysis of the strain curves shows that they include a plasticity region, a stage of linear strain hardening, and a stage of parabolic strain hardening (Taylor hardening). Double-exposure speckle photography is used to visualize the localized strain zones. On that basis, the quantitative deformation characteristics may be obtained. In other words, the displacement-vector field in a plane sample under extension may be determined, and then the components of the plastic distortion tensor (the local elongation exx, shear exy, and rotation ωz) may be calculated. The basic types of plastic flow localization are identified at different stages of strain hardening, and their parameters are determined.

Electrochemical features of plasma electrolytic thermochemical processing of steel and titanium alloys

This review is devoted to an analysis of plasma electrolytic saturation of steel and titanium alloys with light elements (nitrogen, carbon, and oxygen). These technologies have a number of advantages because of the high rates of processes and the low cost of equipment. Electrochemical aspects of the process, which include the formation of a gas–vapor shell, its composition, processes of anodic dissolution, and oxidation and adsorption of a saturating element on the surface processed, are considered. Data of investigations of the mechanism of the release and transport of nitrogen and carbon from the electrolyte into metal are given.

A laboratory device for measuring the diffusion coefficient of hydrogen in metals during their simultaneous hydrogenation and electron irradiation

An upgraded high-vacuum installation and procedure for studying diffusion of hydrogen in a BT1-0 titanium alloy membrane during irradiation of a sample by an electron beam with an energy of 10-120 keV in the scanning and stationary modes and with simultaneous electrolytic saturation are described. For this purpose, deflecting electrodes intended for scanning the beam are additionally integrated into the installation. The mass spectrum of the residual gases was recorded by the partial pressure sensors with a sensitivity as high as 10-13 Pa. The diffusion coefficient of hydrogen measured under the scanning action of the electron beam on the titanium membrane is given.

COMPARISON THE VANADIUM CARBIDE COATING CREATED VIA PLASMA ELECTROLYTIC SATURATION AND TERMO REACTIVE DIFFUSION

One of the most important hardening methods of tool steel is the use of carbide coatings, in which during this process, vanadium diffuses to the specimen’s surface and reacts with carbon. During the Plasma Electrolytic Saturation (PES) Process, the vanadium element diffuses with the help of plasma and increases up to around 1000°C as a result of the temperature, providing conditions for the creation of vanadium carbide. On the other hand, the thermo reactive diffusion (TRD) method during which the specimen is placed inside a salt bath containing the vanadium for a long period of time and the vanadium carbide coating is formed. In this paper, an attempt is made to study the formed coating with the method of plasma electrolytic saturation in addition to comparing the coatings formed by these two methods and obtain some vanadium carbide that created with TRD is purer than PES but that is thinner than plasma method, hardness of coating that created with TRD is about 2500 HV but in TRD is 1100 HV finally. In some PES samples the temperature increase slowly and the maximum temperature is about 120°C, in this condition, the coating is non- diffusion. The hardness of PES coating is about 1100 HV so we can use that in industrial molds.