Improvement Of Electrochemical Behavior Research Articles

The impact of successive laser shock peening on surface integrity and residual stress distribution of laser powder-bed fused stainless steel 316L

Abstract The utilization of laser shock peening (LSP) in laser powder bed fused (LPBF) stainless steel (SS) 316L components enhances the mechanical characteristics and operational lifespan of the product quality through a significant reduction of residual stress and a noticeable increase in roughness parameters. The key objective of the study is to analyze the influence of consecutive laser shock peening (LSP) without ablative coating and low pulse energy on the surface properties, residual stress distribution, and microhardness of samples produced by LPBF with SS316L material. The surface quality of the sample subjected to consecutive laser shock peening shows a slight deterioration in its condition. This can be attributed to the combined impact of ablative surface and surface damage resulting from the production of high-energy plasma. However, the implementation of successive LSP results in a distinctive enhancement of compressive residual stresses (CRS) that are evenly distributed throughout the central axis and sharp edges. In contrast, the as-built condition exhibits non-uniform stress magnitudes. CRS observed in each LSP iteration exhibits a notable increase, reaching a maximum magnitude of −389 MPa compared to the initial stress level of 165 MPa in the as-built sample. This enhancement can be attributed to the repetitive impact of shock waves on the surface, leading to the formation of plastic deformation. The refinement of surface grains and the presence of favorable residual stresses were proven by the utilization of x-ray diffraction (XRD) studies and the Cos α plot. The XRD investigation also indicated the absence of any newly formed phases or secondary phases. A significant enhancement in microhardness was observed, with an increase of 58.3% achieved after the third consecutive peening process. The successive LSP samples displayed a gradual improvement in electrochemical behavior. Though the amplitude parameters increased after LSP, the increase in wear rate was observed.

Corrosion performance of TiAlVN-Ag nanocomposite coating deposited by reactive direct current magnetron sputtering

Surgical devices and tools are manufactured in AISI 420 martensitic stainless steel, due to its hardenability, adequate hardness and acceptable biocompatibility. Nevertheless, many surface modification strategies are being investigated with a view to improving this material by providing it with self-protection against the colonization of bacteria. One such strategy is the use of a TiAlVN-Ag nanocomposite coating to promote bactericidal effect in surgical devices; however, it is necessary to study the electrochemical response of such coatings to aggressive environments that simulate disinfection and sterilization processes. The aim of this work is to study the relationship between the microstructure, chemical phases and the electrochemical and corrosion response of TiAlVN-Ag coating, varying the amount of silver with the target power increase (0, 50, 70, 80 and 100 W). To study the microstructure, chemical phases, scanning and high resolution transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction were used. Roughness, microhardness, residual stresses, qualitative adhesion of coatings were estimated by atomic force microscopy, Knoop indentation, profilometer and Rockwell C indentation, respectively. Electrochemical behavior and corrosion protection of coatings were studied using electrochemical impedance spectroscopy and potentiodynamic polarization. TiAlVN-Ag 50W coating showed an improvement in electrochemical behavior and in protection of the steel against corrosion and exhibiting higher hardness than that of the AISI 420 stainless steel substrates. This coating exhibited a dense microstructure and high crystallinity, indicating that the low Ag content does not affect the insulating nature of the coating matrix.

CoS2 Nanoparticles Embedded in Two‐Dimensional Sheet‐Shaped N‐Doped Carbon for Sodium Storage

AbstractNa‐ion batteries (NIBs) have attracted more and more attention due to the plentiful resources of sodium, excellent ion storage capacity and superior cycle life. However, the implementation of NIBs has been limited by the shortage of electrode materials with outstanding comprehensive properties. Among the discovered anode materials, transition metal sulfides (TMSs) have been widely considered as one of the most competitive and promising ones due to their high theoretical specific capacity. Herein, CoS2 nanoparticles embedded in nitrogen‐doped carbon nanosheets (CoS2/NC) were designed and synthesized by using Co‐based Metal‐organic frame‐work (Co−MOF) as precursor of metal sulfurs, followed by a simple combined carbonization‐sulfurization process. The CoS2/NC compo‐sites were evaluated as binder‐free anode materials for NIBs, delivering a high reversible gravimetric capability of 332 mA h g−1 after 60 cycles as well as great rate capability of 326.6 mA h g−1 at 2000 mA g−1. The improvement of electrochemical behavior is attributed to the synergistic interaction between CoS2 nanoparticles with high electro‐chemical activity and the sheet‐shaped N‐doped carbon with high conductivity. This work provides a greatly attractive strategy for energy conversion and storage.

Preparation of 3D carbon conductive composite derived from nitrogen-rich resin/MWCNT and its application in supercapacitors

Carbon materials are considered as one of the promising materials in supercapacitors because of their distinctive electrochemical properties. In this study, N-doped carbon electrode materials, derived from melamine formaldehyde (MF) resin, a high-performance and N-rich thermosetting resin, used as an electrode active material for supercapacitor application. A simple method was adopted to fabricate the three-dimensional conductive composite materials by mixing the carbon nanotubes (CNTs) to the carbon material with different mass ratios. It was found that the reactant ratio of MF and CNT plays an important role in the improvement of electrochemical behavior. The sample of 7% CNT@MF-C showed a gravimetric specific capacitance of 319.6 F g−1 in 6 M KOH aqueous electrolyte at a current density of 0.5 A g−1, as well as capacitance retention of 97.8% after 10,000 cycles. A remarkable improvement in the electrochemical behavior was obtained by modifying the surface chemistry as well as the electrical conductivity of the carbon. The assembled symmetrical supercapacitors have a high energy density and power density of 9.53 Wh kg−1 and 400 W kg−1, respectively. The presence of porous carbon with intrinsic nitrogen-containing groups makes them more useful as high-performance supercapacitors. Overall, this simple approach exhibits great potential for carbon-based high-performance supercapacitor application.

Feasible synthesis of NCM811 cathodes with controllable Li/Ni cationic mixing for enhanced electrochemical performance via a nano grinding assisted solid‐state approach

This paper reports a feasible approach to offer LiNi0.8Co0.1Mn0.1O2 (NCM811) layered cathode materials with enhanced lattice ordering and improved electrochemical performance through a nano grinding assisted solid-state reaction. Different from the commercial precursor method, oxide raw materials, NiO, CoO and MnO2, rather than the hydroxides, was employed as the starting raw material which was milled into submicron size, pressed into pellets and crushed into granular powder. After calcination under oxygen atmosphere under different temperature, such a simple approach provides layered cathode materials with controllable Li/Ni disordering. Powder XRD results show that when sintered at 800°C, a largest I(003)/I (104) ratio is observed, indicating that the cationic disordering is the lowest, as been confirmed by the XRD refinement data, showing that only 1.08% Ni is misplaced at 3b site. For the electrochemical test, the pNCM800 sample presented an initial specific discharge capacity of 203 mAh/g at 0.1C, together with a capacity retention of 91.77% after 100 cycles at 0.5C. Compared to the value of the sample obtained at normal routine (163.8 mAh/g and 74.85%), the improvement in electrochemical behavior is obvious. Furthermore, the rate performance is also improved, with a specific capacity of 144.1 mAh/g even at 5C rate. The reason for such enhancement could be ascribed to the better kinetic process with low interfacial resistance and fast Li diffusion contributed from the promoted lattice ordering. The results obtained in the experiments greatly indicate the significance of the approach in controlling the Li/Ni disordering, and thus offer an alternative routine for the mass production of layered cathode materials besides the so-called precursor method.

Titania nanotubes dispersed graphitic carbon nitride nanosheets as efficient electrode materials for supercapacitors

Herein, we report the synthesis of a hybrid nanocomposite containing one dimensional (1D) TiO2 nanotube supported over a two dimensional (2D) network of conducting graphitic carbon nitride (g-C3N4) nanosheets by a facile hydrothermal strategy. Symmetric supercapacitors based on the hybrid composite electrodes were fabricated and their electrochemical energy storage performances were evaluated and the results were compared with individual component based supercapacitors. The symmetric supercapacitor based on the composite with 1:4 weight ratios of TiO2 and g-C3N4 exhibited a remarkable increase in the specific capacitance in comparison with the individual components. The improvement in electrochemical behavior of the composite sample was attributed to the increase in surface area of the composite due to the spacer effect of titania nanotubes in the 2D g-C3N4 nanosheets.

Polybenzoxazine originated N-doped mesoporous carbon ropes as an electrode material for high-performance supercapacitors

In this study, N-doped mesoporous carbon ropes (N-MCRs), derived from polybenzoxazine, a new high-performance thermosetting resin, used as an electrode active material for supercapacitor application. Nitrogen-containing tetraethylenepentamine and eugenol were used to synthesize polybenzoxazine. The structure of the monomer was supported by Fourier transform infrared (FT-IR) and 1H NMR spectroscopy. The morphology and surface properties of the synthesized N-MCRs were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), N2 adsorption-desorption study and X-ray photoelectron spectroscopy (XPS). It was found that the reactant ratio of nitrogen-rich polybenzoxazine plays an important role in the improvement of electrochemical behavior. The BET surface area of N-MCRs was found to be 300 m2 g−1. Electrochemical performance proposes a high nitrogen content of 12.38 mol % with optimum nitrogen-containing benzoxazine derived carbon backgrounds. It showed a specific capacitance of the 60 F g−1 in 2 M KOH aqueous electrolyte at a current density of 1 A g−1. A remarkable improvement in the electrochemical behavior was obtained by modifying the surface chemistry as well as the electrical conductivity of the carbon. The presence of porous carbon with intrinsic nitrogen-containing groups makes them more useful as high-performance supercapacitor. Overall, this simple approach exhibits great potential for carbon-based high-performance supercapacitor application.

LiNi0.8Co0.15Al0.05O2: Enhanced Electrochemical Performance From Reduced Cationic Disordering in Li Slab

Sub-micron sized LiNi0.8Co0.15Al0.05O2 cathode materials with improved electrochemical performance caused by the reduced cationic disordering in Li slab were synthesized through a solid state reaction routine. In a typical process, spherical precursor powder was prepared by spray drying of a uniform suspension obtained from the ball-milling of the mixture of the starting raw materials. Then the precursor powders were pressed into tablets under different pressures and crushed into powder. The pressing treated powders were finally calcinated under oxygen atmosphere to obtain the target cathode materials. XRD investigation revealed a hexagonal layered structure without impurity phase for all samples and significant increase in the diffraction intensity ratio of I(003)/I(104) was observed. Rietveld refinement further confirmed the reduced cationic disordering in Li slab by such pressing treatment, and the smallest disordering was observed for sample S4 with only 1.3% Ni ions on Li lattice position. The electrochemical testing showed an improvement in electrochemical behavior for those pressing treated samples. The calculation of diffusion coefficients using EIS data showed improved Li diffusion coefficient after pressing treatment. The sample S4 presented a diffusion coefficient of 4.36 × 10−11 cm2·s−1, which is almost 3.5 times the value of untreated sample.

Improving electrochemical properties of AISI 1045 steels by duplex surface treatment of plasma nitriding and aluminizing

Improvement in electrochemical behavior of AISI 1045 steel after applying aluminum nitride coating was investigated in 3.5% NaCl solution, using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) analyses. Aluminum nitride coating was applied on the steel surface by duplex treatment of pack aluminizing and plasma nitriding. Some specimens were plasma nitrided followed by aluminizing (PN–Al), while the others were pack aluminized followed by plasma nitriding (Al–PN). Topological and structural studies of the modified surfaces were conducted using scanning electron microscope (SEM) equipped by energy dispersive X-ray spectroscope (EDS), and X-ray diffractometer (XRD). The electrochemical measurements showed that the highest corrosion and polarization (Rp) resistances were obtained in PN–Al specimens, having single phase superficial layer of AlN. Pitting mechanism was dominant reason of lower corrosion resistance in the Al–PN specimens.

Co3O4@layered double hydroxide core/shell hierarchical nanowire arrays for enhanced supercapacitance performance

Co3O4@NiAl-layered double hydroxide (LDH) core/shell nanowire arrays with hierarchical structure have been synthesized by in situ growth of LDH nanosheets shell on the surface of Co3O4 nanowire arrays. The resulting Co3O4@NiAl-LDH material exhibits promising supercapacitance performance with largely enhanced specific capacitance and rate capability, much superior to pristine Co3O4 nanowire arrays. The improvement in electrochemical behavior is attributed to the hierarchically mesoporous morphology and the strong core–shell binding interaction, which facilitates a sufficient exposure of electroactive species as well as the charge transportation process. This work provides a facile and effective strategy for the fabrication of hierarchical materials with core/shell structure, which can be potentially used in the energy storage and conversion devices.

Effect of surface modifiers in improving the electrochemical behavior of LiNi0.4Mn0.4Co0.2O2 cathode

Surface modification of LiNi0.4Mn0.4Co0.2O2 (442) compound with certain metal oxides viz., Al2O3, Bi2O3 and In2O3 has been attempted with a view to improve the structural and cycling stability, especially upon high voltage and high rate cycling conditions. In addition to HF scavenging effect, the protective metal oxide inter-connect layer restricts the number of oxide ion vacancies eliminated during the initial cycling of cathode, resulting in the reduced irreversible capacity loss of the first cycle. Among the surface modified cathodes, Bi2O3 coated LiNi0.4Mn0.4Co0.2O2 cathode exhibits appreciable specific capacity values of 196mAhg−1 (Qdc1) and 175mAhg−1 (Qdc100) with 89% capacity retention, thus evidencing the superiority of Bi2O3 modifier in improving the electrochemical behavior of pristine LiNi0.4Mn0.4Co0.2O2 cathode. Further, suitability of Bi2O3 coated LiNi0.4Mn0.4Co0.2O2 cathode for high voltage (5.0V) and high rate (3C) lithium intercalation and de-intercalation applications has been demonstrated up to 100 cycles. Based on the extent of improvement in electrochemical behavior, the cathodes under investigation could be arranged in the order: Bi2O3 coated>Al2O3 coated>In2O3 coated>uncoated LiNi0.4Mn0.4Co0.2O2 oxide.

Improvement of Corrosion Resistance and Structural Change in 304 Stainless Steel by means of Ion-Mixing

High-energy ion-beam mixing technique was applied for the surface modification of austenitic stainless steel, followed by electrochemical characterization and microstructural observation. The co-mixing of silicon and chromium resisted the passivation current to 1/1000 relative to the un-modified condition. The corrosion resistance improved remarkably. Microstructural observation revealed that the enhanced diffusion and induced amorphous structure introduced by the co-mixing of silicon and chromium, which played a very important role in the improvement of electrochemical behavior at surface.