High–Energy‐Storage Density Capacitors of Bi(Ni1/2Ti1/2)O3–PbTiO3 Thin Films with Good Temperature Stability

High–energy‐storage density capacitors with thin films of 0.5Bi(Ni_1/2Ti_1/2)O₃–0.5PbTiO₃ (BNT–PT) were fabricated by chemical solution deposition technique on Pt/Ti/SiO₂/Si substrates. The dense thin films with pure‐phase perovskite structure could be obtained by annealing at 750°C. High capacitance density (~1925 nF/cm² at 1 kHz) and extremely high‐energy density (~45.1 J/cm³) under an electric field of 2250 kV/cm were achieved at room temperature. The energy‐storage density and efficiency varied little in a wide temperature range from ?190°C to 250°C. The high–energy‐storage density and good temperature stability make BNT–PT films promising candidates for high power electric applications.     

The microstructural features and corrosion behavior of Hydroxyapatite/ZnO nanocomposite electrodeposit on NiTi alloy: Effect of current density

In the present study, hydroxyapatite/ZnO nanocomposite coatings were developed on NiTi superelastic alloy via pulse electrodeposition technique under three different current densities. The morphological observations (FESEM) indicated that under 6 mA/cm², a compact, uniform composite layer could form, whereas lower or higher current densities resulted in non-uniform, porous coatings with uneven distribution of nanoparticles. XRD and FTIR studies revealed that pure hydroxyapatite was not achieved below 6 mA/cm². Topographic features (AFM) were assessed and demonstrated a continuous rise in roughness parameters as current density increased. The corrosion behavior was investigated through potentiodynamic polarization as well as impedance spectroscopy techniques. According to the extracted data, the porosity and non-uniformity of coatings formed under 3 and 9 mA/cm² caused a detrimental effect on the corrosion resistance of surfaces. The layer obtained under 6 mA/cm² showed resistance (R_c) which was almost two times greater than those deposited under 3 and 9 mA/cm² current densities. Last but not least, the bioactivity of coatings was evaluated in simulated body fluid. It was observed that more compact deposits offered more active sites for apatite nucleation, resulting in refined cauliflower-like grains. Accordingly, it can be asserted that the best composite coating was achieved under 6 mA/cm² current density.     

The Influence of Temperature and Composition on the Operation of Al Anodes for Aluminum‐Air Batteries

The influence of composition and temperature on the anode polarization and corrosion rate of pure Al and Al‐In anodic alloys in 8M NaON electrolyte has been investigated. High current density (more than 800 mA cm⁻²) and faradaic efficiency over 97% were observed for all investigated alloys at 60 °C. Lower temperature provides lower current density (200–300 mA cm⁻² at 40 °C, and less than 100 mA cm⁻² at 25 °C). Different formation of the product reaction layers was observed for pure aluminum and Al–0.41In alloy, leading to the different polarization character of the samples. The comparison of two Al‐In alloys with similar composition has been carried out. Al–0.45In alloy having a coarse‐grained structure had a more positive no‐current potential and lower value of anode limiting current (200 mA cm⁻² vs. 300 mA cm⁻²) compared with the fine‐grained Al–0.41In alloy, as well as greater parasitic corrosion rate and greater no‐current corrosion. The current‐voltage, power and discharge characteristics of the aluminum‐air cell with Al–0.41In anode and gas diffusion cathode have been investigated. Open circuit voltage of the cell is 1.934 V and the maximum power density of the cell is 240 mW cm⁻² at the voltage of 1.3 V.     

CO2‐Tolerant Ceramic Membrane Driven by Electrical Current for Oxygen Production at Intermediate Temperatures

In this work, an electrochemical oxygen pump ceramic membrane based on Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte and La_0.6Sr_0.4FeO_3?δ (LSF) electrode was prepared and characterized by XRD, SEM, and EDX. The area specific resistance of the membranes was measured by impedance spectroscopy. The oxygen electrical permeation behavior of SDC/LSF membrane was investigated under different operating conditions. In consistent with the theoretical prediction from Faraday law, the oxygen flux value observed is closely correlated in quantity with the applied current density. The permeation (or Faraday) efficiency of SDC/LSF membrane could reach above 95% at lower temperatures (600°C–700°C). At 700°C, the oxygen flux through SDC/LSF membrane with 3000 mA/cm² current density could reach ~9.97 mL/cm²/min. In addition, the prepared SDC/LSF membrane electrical performance was also tested under the presence of CO₂. It was found that SDC/LSF membrane has excellent structure and permeation stability against CO₂ gas, reflecting its potential applications like oxyfuel technologies and hydrocarbon oxidations.     

Crosslinked hydroxyl‐conductive copolymer/silica composite membranes based on addition‐type polynorbornene for alkaline anion exchange membrane fuel cell applications

Crosslinked hydroxyl‐conductive copolymer/silica composite membranes based on addition‐type polynorbornene, poly(dodoxymethylene norbornene‐co‐norbornene‐3‐(trimethylpropyl ammonium)‐functionalized silica (QP(DNB/NB‐SiO₂), were prepared by a sol–gel method. Copolymer composite membranes with different degree of quaternary ammonium functional silica, designated as QP(DNB/NB‐SiO₂‐X) (X = 5, 10, 15 and 25 wt%, respectively), displayed good dimensional stabilities with low in‐plane swelling rate of 1.32–3.7%, good mechanical properties with high elastic modulus of 605.4–756.8 MPa and high tensile strength of 13.2–20 Mpa. The achieved copolymer composite membranes could self‐assemble into a microphase‐separated morphology with randomly oriented long‐range aliphatic chain/cylinder ionic channels that were imbedded in the hydrophobic PNB matrix. Among these membranes, the QP(DNB/NB‐SiO₂‐25) showed the parameter with ionic conductivity of 9.33 × 10^?3S cm^?1, methanol permeability of 2.89 × 10^?7cm² s^?1, and ion‐exchange capacity(IEC) of 1.19 × 10^?3 mol g^?1. A current density of 82.3mA cm^?2, the open circuit voltage of 0.65 V and a peek power density of 32 mW cm^?2 were obtained. POLYM. ENG. SCI., 58:13–21, 2018. © 2017 Society of Plastics Engineers     

Sr2Fe1.5Mo0.5O6–δ – Zr0.84Y0.16O2–δ Materials as Oxygen Electrodes for Solid Oxide Electrolysis Cells

The high‐temperature solid oxide electrolysis cell (SOEC) is one of the most promising devices for hydrogen mass production. To make SOEC suitable from an economical point of view, each component of the SOEC has to be optimized. At this level, the optimization of the oxygen electrode is of particular interest since it contributes to a large extent to the cell polarization resistance. The present paper is focused on an alternative oxygen electrode of Zr_0.84Y_0.16O_2–δ‐Sr₂Fe_1.5Mo_0.5O_6–δ (YSZ‐SFM). YSZ‐SFM composite oxygen electrodes were fabricated by impregnating the YSZ matrix with SFM, and the ion‐impregnated YSZ‐SFM composite oxygen electrodes showed excellent performance. For a voltage of 1.2 V, the electrolysis current was 223 mA cm⁻², 327 mA cm⁻² and 310 mA cm⁻² at 750 °C for the YSZ‐SFM10, YSZ‐SFM20, and YSZ‐SFM30 oxygen electrode, respectively. A hydrogen production rate as high as 11.46 NL h⁻¹ has been achieved for the SOEC with the YSZ‐SFM20 electrode at 750 °C. The results demonstrate that YSZ‐SFM fabricated by impregnating the YSZ matrix with SFM is a promising composite electrode for the SOEC.     

A Coated Infiltration Growth Technique for Fabricating Single‐Grain Y–Ba–Cu–O Bulk Superconductor

A coated infiltration growth technique was proposed to fabricate single‐grain Y?Ba?Cu?O bulk superconductor, in which a liquid source coated Y₂BaCuO₅ (Y‐211) preform was employed and the liquid source composition was 3BaO + 5CuO. Experimental results indicated that, the sample exhibited a single‐grain morphology on the top surface, and the liquid source coating always existed surrounding the bulk which contributed to the complete growth of the sample. The homogeneous distribution of fine Y‐211 inclusions in microstructure and a satisfactory J_c performance of 5.67 × 10⁴ A/cm² in self‐field at 77 K have also been observed.     

Iron oxide supercapacitor of high volumetric energy and power density using binder-free supersonic spraying and self-healing rGO

Iron oxide (Fe₂O₃) nanoparticles and reduced graphene oxide (rGO) sheets were supersonically sprayed onto a nickel substrate to fabricate flexible supercapacitors. The supersonic impact velocity was adjusted by varying the air chamber pressure from 2 to 6 bar, which facilitated the self-healing of Stone-Wall defects in rGO sheets. Supersonic spraying caused exfoliation of the rGO sheets, which in turn increased the surface area and adherence of the Fe₂O₃ nanoparticles. The optimal case exhibited a specific capacitance of 1.44 F?cm^-2 at a current rate of 1.5 mA?cm^-2 and the energy density was 14.23 mWh?cm^-3 at 250 mW?cm^-3. The width of the potential window increased to 1.4 V, implying a significant increase in the energy storage capability. The energy density of the supersonically sprayed Fe₂O₃/rGO electrode also showed no signs of deterioration even when the increased current density interfered with the electrode performance.     

Electrochemical Performance of MnO2‐based Air Cathodes for Zinc‐air Batteries

This paper compares the oxygen reduction on four MnO₂‐based air cathodes assembled in home‐made electrochemical cells, with some particular observations on α‐MnO₂ cathode. The results show that the catalytic activity decreases in the following order: electrolytic MnO₂ (EMD) > natural MnO₂ (NMD) > β‐MnO₂ > α‐MnO₂. The maximum power density of the zinc‐air battery with EMD as the catalyst reaches up to 141.8 mW cm⁻² at the current density of 222.5 mA cm⁻², which is about 60%, 20% and 10% higher than that of α‐MnO₂ (90.0 mW cm⁻² at 120.3 mA cm⁻²), β‐MnO₂ (121.5 mW cm⁻² at 150.4 mA cm⁻²) and NMD (128.2 mW cm⁻² at 207.8 mA cm⁻²), respectively. It is believed that its unique crystal structure and biggest BET surface area make EMD have the smallest charge transfer resistance (R_ct), thus EMD has the highest activity.     

Expanded Graphite–Epoxy–Flexible Silica Composite Bipolar Plates for PEM Fuel Cells

Silica impregnated expanded graphite–epoxy composites are developed as bipolar plates for proton exchange membrane (PEM) fuel cells. These composite plates were prepared by solution impregnation, followed by compression molding and curing. Mechanical properties, electrical conductivities, corrosion resistance, and contact angles were determined as a function of impregnated content. The plates show high flexural strength with 5% methyltrimethoxysilane (MTMS) addition (20 MPa) and in‐plane conductivity of 131 S cm⁻¹ that meet the DOE target (>100 S cm⁻¹). Corrosion current values as low as 1.09 μA cm⁻² were obtained. The contact angle was found to be 80°. Power density of 1 W cm⁻² was achieved with custom made expanded graphite–polymer composite plates. High efficiency values were obtained at low current regions.     

The high temperature oxidation and thermal shock behavior of a dense WSi2–TaSi2 coating on Ta substrate prepared by a novel two-step process

In order to improve the oxidation resistance of the Ta substrate, a novel two-step process including molten salt electrodeposition (Na₂WO₄-WO₃ system) and halide activated pack cementation was adopted to prepare a WSi₂–TaSi₂ coating on tantalum substrate. During the electrodeposition process, dense tungsten coatings were fabricated at current densities of 30 mA/cm², 40 mA/cm² and 50 mA/cm². It was observed that the grain size exhibited a log-normal distribution. When the current density was 40 mA/cm², the grain size and flattest surface of the tungsten coating reached 9.50 ± 0.23 μm and 6.792 μm, respectively. When performing the static oxidation test, the WSi₂–TaSi₂ coating could effectively protect the Ta substrate oxidized at 1600 °C for 30 h. This is attributed to the presence of dense SiO₂ and Ta₂O₅, which acted as a protective layer and suppressed the further penetration of oxygen. Furthermore, due to the matching thermal expansion coefficient between each layer and the sealing ability of semi-molten SiO₂, the four-layer SiO₂–W₅Si₃–WSi₂–Ta₅Si₃ coating could successfully pass 721 thermal shock tests from 1600 °C to room temperature.     

Novel BiFeO3–BaTiO3–Ba(Mg1/3Nb2/3)O3 Lead‐Free Relaxor Ferroelectric Ceramics for Energy‐Storage Capacitors

A novel lead‐free relaxor ferroelectric ceramic of (0.67?x)BiFeO₃–0.33BaTiO₃–xBa(Mg_1/3Nb_2/3)O₃ [(0.67?x)BF–0.33BT–xBMN, x = 0–0.1] was prepared by a solid‐state reaction method. A relatively high maximum polarization P_max of 38 μC/cm² and a low remanent polarization P_r of 5.7 μC/cm² were attained under 12.5 kV/mm in the x = 0.06 sample, leading to an excellent energy‐storage density of W ~1.56 J/cm³ and a moderate energy‐storage efficiency of η ~75%. Moreover, a good temperature stability of the energy storage was obtained in the x = 0.06 sample from 25°C to 190°C. The achievement of these characteristics was basically attributed to an electric field induced reversible ergodic to ferroelectric phase transition owing to similar free energies near a critical freezing temperature. The results indicate that the (0.67?x)BF–0.33BT–xBMN lead‐free realxor ferroelectric ceramic could be a promising dielectric material for energy‐storage capacitors.     

Relaxor Ferroelectric BaTiO3–Bi(Mg2/3Nb1/3)O3 Ceramics for Energy Storage Application

Perovskite solid solution ceramics of (1 ? x)BaTiO₃–xBi(Mg_2/3Nb_1/3)O₃ (BT–BMN) (x = 0.05–0.2) were synthesized by solid‐state reaction technique. The results show that the BMN addition could lower the sintering temperature of BT‐based ceramics. X‐ray diffraction results reveal a pure perovskite structure for all studied samples. Dielectric measurements exhibit a relaxor‐like characteristic for the BT–BMN ceramics, where broadened phase transition peaks change to a temperature‐stable permittivity plateau (from ?50°C to 300°C) with increasing the BMN content (x = 0.2), and slim polarization–electric field hysteresis loops were observed in samples with x ≥ 0.1. The dielectric breakdown strength and electrical resistivity of BT–BMN ceramics show their maxima of 287.7 kV/cm and 1.53 × 10¹³ Ω cm at x = 0.15, and an energy density of about 1.13 J/cm³ is achieved in the sample of x = 0.1.     

The evaluation of nickel deposit obtained via Watts electrolyte at ambient temperature

A series of electroplating works were conducted to investigate the best conditions for the electrodeposition of nickel on a mild steel substrate. The electrodeposition was done at ambient electrolyte temperature with mild agitation and under current density ranging from 10 to 50 mA/cm². X-ray diffraction analysis (2θ for first three peaks = 44.6, 51.9, and 76.8) and Energy Dispersive Spectrometer verified the presence of a pure nickel coating. Under field emission scanning electron microscopy analysis, the coating shows a typical nodular surface morphology, while cross-sectional microstructures show a compact nickel layer. Vickers hardness testing shows that the coating hardness gave the highest value of 293 HV at 30 mA/cm² current density.     

Fabrication of Transparent Spinel Honeycomb Structures by Methyl Cellulose–Based Thermal Gelation Processing

Transparent MgAl₂O₄ spinel of flat as well as honeycomb structure was fabricated by employing thermally induced gel casting of the slurry with 56 wt% solid loading containing 0.2 wt% of methylcellulose. The green specimens were pressureless sintered to 98%–99% of theoretical density with no open porosity at an optimum temperature of 1700°C. Final densification by hot isostatic pressing of both the specimens at the optimum temperature of 1800°C and 195 MPa pressure enabled further elimination of residual porosities and full densification resulting in theoretical density of 3.58 g/cc. The design of the honeycomb was such that it exhibited a surface area to volume ratio of 0.65 cm²/cm³ and a relative density of 0.69. The hardness of the honeycomb specimens has been found to be 13 GPa, which is at par with the solid specimens processed under identical conditions. Solid specimens of around 4 mm thickness exhibited a transmission of >80% in the visible (0.4–0.8 μm) region. Specimens were also tested according to ASTM procedures and have shown a flexural strength (σ_f) of 195 MPa and plane‐strain fracture toughness (K_Ic) of 1.87 MPa·m^1/2 as reported in this study.     

Multifunctional polyaniline–tin oxide (PANI–SnO2) nanocomposite: Synthesis,electrochemical, and field emission investigations

Synthesis of PANI–SnO₂ nanocomposite has been performed using a simple two step chemical oxidative polymerization route. The structural, morphological and chemical properties of the as‐synthesized PANI–SnO₂ nanocomposite have been revealed by various characterization techniques such as SEM, TEM, XRD, FTIR, and XPS. Interestingly the as‐synthesized PANI–SnO₂ nanocomposite exhibits supercapacitance value of 721 F g^?1 with energy density 64 Wh kg^?1, which is noticed to be higher than that of pristine SnO₂ and PANI nanostructures. Furthermore, the galvanostatic charge–discharge characteristics revealed pseudocapacitive nature of the PANI–SnO₂ nanocomposite. The estimated values of charge transfer resistance and series resistance estimated from the Nyquist plot are found to be lower. Along with the supercapacitive nature, PANI–SnO₂ nanocomposite showed promising field emission behavior. The threshold field, required to draw emission current density of 1 μA/cm², is observed to be 0.90 V/μm and emission current density of 1.2 mA/cm² has been drawn at applied field of ～2.6 V/μm. The emission current stability investigated at preset values of 0.02 and 0.1 mA/cm² is observed to be fairly stable over duration of more than 3 h. The enhanced supercapacitance values, as well as, the promising field emission characteristics are attributed to the synergic effect of SnO₂ nanoparticles and PANI nanotubes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41401.     

Effects of CuO Addition on Electrical Properties of 0.6BiFeO3–0.4(Bi0.5K0.5)TiO3 Lead‐Free Piezoelectric Ceramics

0.6BiFeO₃–0.4(Bi_0.5K_0.5)TiO₃ (0.6BF–0.4BKT) ceramic samples with 0.0–4.0 mol% CuO were prepared by the solid‐state reaction. The CuO addition aided the densification of the samples and slightly increased the lattice constant. The relaxor‐like defuse dielectric peak of 0.6BF–0.4BKT became sharper with increasing the CuO content. Polarization–electric field curve of the undoped 0.6BF–0.4BKT was a pinched loop in the as‐sintered state, while that was a square hysteresis with a large remanent polarization of 48 μC/cm² after the thermal quenching, demonstrating a strong domain wall pinning due to defect dipoles. We found that the CuO addition up to 2.0 mol% facilitates the polarization switching in the as‐sintered samples to increase the remanent polarization and the piezoelectric d₃₃ coefficient. The results of the structural and electrical investigations suggested that the copper ion acts as a donor in 0.6BF–0.4BKT by compensating the potassium vacancy created by the evaporation of K₂O during the calcination and sintering processes.     

Optimization of wear–corrosion properties of a–C:N films using filtered cathodic arc deposition

Applying a 4-factor (negative substrate bias voltage, arc current, Ar flow and N₂/Ar ratio) 3-level (L9) orthogonal array design using the Taguchi method to optimize the wear–corrosion properties of a–C:N in Filtered Cathodic Vacuum Arc (FCVA) deposition was investigated. The influence of N₂/Ar ratio, over the range of 1/6 to 2/3, is shown by the increase in the following: the wear–corrosion current density changes from 36 to 78 nA/cm², and the friction coefficient changes from 0.042 to 0.086. A higher N₂/Ar ratio induces the a–C:N film's structure to reduce the sp³ content (sp² rich) which implies the formation of loose networks due to N₂ incorporation. Based on the analysis, the N₂/Ar ratio is the most significant control factor as its percentage contribution is 69% for wear–corrosion current density and 32% for frictional coefficient, respectively. There is a tendency for a higher friction coefficient by increasing the following three factors; level of negative substrate bias voltage, Ar flow and N₂/Ar ratio. We observed an increase of N content and sp² bonding which correlated to the decrease of hardness and an also rougher a–C:N surface with increasing the factors level. Over the design range of 4 factors, the optimum wear–corrosion properties and friction coefficient obtained from the Taguchi analysis were obtained using a 20 V negative substrate bias, 30 A arc current, 30 sccm Ar flow and 1/6 N₂/Ar ratio respectively. Overall, the results show an optimum design when compared with the current design as it was able to reduce 84% of the wear–corrosion current density (35.7 down to 5.6 nA/cm²) and 58% of the frictional coefficient (0.060 down to 0.025), respectively.     

Well‐functioned photovoltaics based on nanofibers composed of PBDT‐TIPS‐DTNT‐DT and graphenic precursors thermally modified by polythiophene,polyaniline and polypyrrole

Reduced graphene oxide nanosheets modified by conductive polymers including polythiophene (GPTh), polyaniline (GPANI) and polypyrrole (GPPy) were prepared using the graphene oxide as both substrate and chemical oxidant. UV–visible and Raman analyses confirmed that the graphene oxide simultaneously produced the reduced graphene oxide and polymerized the conjugated polymers. The prepared nanostructures were subsequently electrospun in mixing with poly(3‐hexylthiophene) (P3HT)/phenyl‐C71‐butyric acid methyl ester (PC₇₁BM) and poly[bis(triisopropylsilylethynyl)benzodithiophene‐bis(decyltetradecylthien)naphthobisthiadiazole] (PBDT‐TIPS‐DTNT‐DT)/PC₇₁BM components and embedded in the active layers of photovoltaic devices to improve the charge mobility and efficiency. The GPTh/PBDT‐TIPS‐DTNT‐DT/PC₇₁BM devices demonstrated better photovoltaic features (J_sc = 11.72 mA cm^?2, FF = 61%, V_oc = 0.68 V, PCE = 4.86%, μ_h = 8.7 × 10^?3 cm² V^–1 s^?1 and μ_e = 1.3 × 10^?2 cm² V^–1 s^?1) than the GPPy/PBDT‐TIPS‐DTNT‐DT/PC₇₁BM (J_sc = 10.30 mA cm^?2, FF = 60%, V_oc = 0.66 V, PCE = 4.08%, μ_h = 1.4 × 10^?3 cm² V^–1 s^?1 and μ_e = 8.9 × 10^?3 cm² V^–1 s^?1) and GPANI/PBDT‐TIPS‐DTNT‐DT/PC₇₁BM (J_sc = 10.48 mA cm^?2, FF = 59%, V_oc = 0.65 V, PCE = 4.02%, μ_h = 8.6 × 10^?4 cm² V^–1 s^?1 and μ_e = 7.8 × 10^?3 cm² V^–1 s^?1) systems, assigned to the greater compatibility of PTh in the nano‐hybrids and the thiophenic conjugated polymers in the bulk of the nanofibers and active thin films. Furthermore, the PBDT‐TIPS‐DTNT‐DT polymer chains (3.35%–5.04%) acted better than the P3HT chains (2.01%–3.76%) because of more complicated conductive structures. © 2019 Society of Chemical Industry     

Erosive and corrosive wear performance and characterization studies of plasma-sprayed WC/Cr3C2 coating on SS316

Plasma spray coating with ceramic carbide is a promising approach for improving the surface quality of the materials. In this work, the effectiveness of tungsten carbide (WC), chromium carbide (Cr₃C₂), and the composite coating of the two powders in the weight ratio of 50:50 were investigated. In the erosion test, aluminum oxide (Al₂O₃) particles were combined with a high-speed air-jet and impinged at 90° on the top surface of the material. Electrochemical polarization and electrochemical impedance spectroscopy studies were conducted with a 3.5 wt.% of sodium chloride (NaCl) solution as the electrolyte. Using a scanning electron microscope, the surface morphology of powders and coatings, as well as the mechanisms of erosion and corrosion, were studied. Energy-dispersive X-ray analysis and X-ray diffractometry were used to reveal the composition and elemental distribution of the feedstock powders and coatings. Because of the presence of hard phases, the composite coating shows the highest average microhardness of 1350.2 HV. The composite coating exhibits improved erosive wear resistance with an increase in erodent exposure time. The Cr₃C₂ coating has a reduced corrosion current density of 1.404 × 10⁻⁵ mA/cm² and a higher charge transfer resistance of 2086.75 Ω cm² due to passivation.