Effect of carbon coating on the electrochemical properties of La–Y–Ni-based hydrogen storage alloys

The A₂B₇-type (LaSmY) (NiMnAl)_3.5 alloys were prepared by induction melting, and then the alloy samples coated with different contents of nano-carbon were prepared by the mixing and sintering method using pitch as carbon source. The effects of the contents and structure of the coated-carbon on the electrochemical properties of alloy samples were investigated. With the carbon content increase from 0.1 to 1.0 wt%, the cyclic stability is improved and the high-rate dischargeabilitiy (HRD) of the alloy electrodes first increase and then decrease. The kinetic results show that the carbon coating improves the electrocatalytic activity and electrical conductivity of the alloy electrodes. The alloy electrode with 0.5 wt% carbon coating exhibits the best electrochemical properties. The maximum discharge capacity (C_max) is 345.7 mAh·g⁻¹, the HRD₁₂₀₀ is 72.49%, and the capacity retention rate (S₃₀₀) is 79.44%.     

LiPF6–EC–EMC electrolyte for Li-ion battery

We studied the effect of salt concentration and solvent ratio on the cycling performance of LiMn₂O₄ cathode and graphite anode in LiPF₆–ethylene carbonate (EC)–ethyl methyl carbonate (EMC) electrolytes. The results show that solvent ratio has negligible impact on the performance of both electrodes but does affect the issues of thermal compatibility and ionic conductivity. Salt concentration affects the performance in two reverse ways: LiMn₂O₄ cathode requires low concentration, while graphite anode requires high concentration. It is observed that, during the first cycle, both electrodes produce irreversible capacity and form a solid electrolyte interface (SEI) film on their surface. From the view point of operation at low temperatures, 1 M LiPF₆ 3:7 EC–EMC is recommended for Li-ion cells.     

Charge–discharge characteristics of LiCoO2/mesocarbon microbeads battery with poly(vinyl chloride)-based composite polymer electrolyte

Polyvinyl chloride (PVC)-based composite polymer electrolyte films consisting of PVC–LiCF₃SO₃–SiO₂ are prepared by the solution-casting method. The electrical properties of the electrolyte are investigated for ionic conductivity and its dependence on temperature. The electrolyte with the highest ionic conductivity is used to fabricate a LiCoO₂/PVC–LiCF₃SO₃–SiO₂/mesocarbon microbeads (MCMB) battery. The charge–discharge characteristics and performance of the battery at room temperature are evaluated to ascertain the effective viability, of these solid electrolytes in lithium-polymer batteries. Battery performances is also investigated at 313, 323 and 333 K.     

Controllable synthesis of Co/MnO heterointerfaces embedded in graphitic carbon for rechargeable Zn–air battery

Owing to the unique geometric and electronic structure, design and synthesis of electrocatalysts with well defined heterointerfaces are essential for clean energy technologies, for instance water-splitting and Zn-air batteries. Herein, a bifunctional electrocatalyst assembled by Co/MnO nanoparticles and nitrogen doping double-sphere carbon (denoted as Co/MnO@N-DSC), was fabricated via a solvothermal and pyrolysis strategy. The Co/MnO@N-DSC catalysts exhibit an enhanced bifunctional oxygen electrocatalytic performance for Oxygen reduction reaction (ORR) (E_1/2, 0.84 V vs. RHE) and oxygen evolution reaction (OER) (E_onset, 1.54 V vs. RHE). As an air cathode catalyst, the Co/MnO@N-DSC-based Zn-air battery can afford prime performance, over the commercial noble-metal-based Zn-air battery. Theoretical calculation results indicate that the synergism of Co (111)/MnO (200) heterointerfaces can enhance charge transfer and provide extra electrons for the reaction processes. This work provides a promising manoeuvre to uplift bifunctional catalytic activity by increasing the synergy from heterointerfaces of transition-metal/metal oxide in oxygen electrocatalysis.     

Hydrogen absorption properties of carbon supported Pd–Ni nanoalloys

Carbon supported Pd–Ni nanoalloys with well controlled composition and particle size distribution were synthesized by incipient wetness impregnation method. The Pd-rich nanoalloys (10 and 20 Ni at.%) form a hydride phase at atmospheric pressure and ambient temperature whereas, no hydride formation is observed for higher Ni content (30 at%), as determined by Pressure-Composition-Isotherms and in situ X-ray diffraction. Significant thermodynamic changes for hydride forming Pd–Ni nanoalloys are noticed as compared to pure Pd, in agreement with the bulk counterparts: the enthalpy of the hydride formation of Pd–Ni nanoalloys decreases by increasing the Ni content. These thermodynamic changes are not related to downsizing of particles but rather to an alloying effect. The solely effects of particle downsizing are the sloping and the shortening of the plateau observed in the PCI curves.     

Physical properties of the CNT:TiO2 thin films prepared by sol–gel dip coating

Uniform and highly adherent thin films of CNT:TiO₂ were synthesized by sol–gel dip coating method. Both TiO₂ and CNT:TiO₂ films showed very identical structural characteristics and no significant changes in the lattice values were observed. The crystalline size decreased from 20 nm for TiO₂ film to 17 nm for the 4%CNT:TiO₂ film. The film surface was very smooth and compact, as indicated by the roughness data obtained from AFM measurements; the root mean square (rms) average of the roughness was as low as 3 nm. The HRTEM showed that the CNTs are embedded in the matrix of TiO₂ indicating the formation of a composite. In Raman spectra the characteristic vibrations of the TiO₂ are identified, the increase in the FWHM of main anatase peak (144 cm^?1) in the case of the 4%CNT:TiO₂ film is interpreted as due to the incorporation of CNTs in the film. At the wavelength of 600 nm the refractive index of pure TiO₂ was 2.07 and the 4%CNT:TiO₂ showed a value of 2.29. The photoresponse curves showed typical features of charge trapping centers in the band gap of the films.     

Effects of Cu substrate morphology and phase control on electrochemical performance of Sn–Ni alloys for Li-ion battery

The influence of substrate morphology and ageing on the charge–discharge performance of a Sn–Ni alloy anode electrodeposited on a Cu substrate are examined. The Sn–Ni alloy (Sn 82 at.%–Ni 18 at.% anode) shows a high capacity of around 480 mAh g⁻¹ up to 12 cycles, but its capacity rapidly fades with cycling. The initial capacity and the cyclic properties of the alloy electrode are significantly improved when the surface morphology of the Cu substrate is changed from smooth-type to nodule-type. Optimized ageing treatment leads to further enhancement in the charge–discharge performance of the anode. The increase in the capacity and better cyclic properties are attributed to stronger adhesion between the Si–Ni anode and the Cu substrate. This is induced by inter-locking of the nodule-type Cu substrate and a buffering effect of Cu–Sn intermetallic compounds formed during ageing.     

Microstructure and electrochemical properties of Zr–Ti–V–Ni–Mn–LM alloys for application in Ni–MH secondary battery

A series of multi-component Zr_1−xTi_xV_0.4Ni_1.2Mn_0.4LM_y (x=0.3, 0.4; y=0.0,0.02,0.05,0.1,0.2,0.3, LM; lantanum-rich-mischmetal) alloys are prepared and their crystal structure and P–C–T curves are analyzed. The alloys have been modified by adding LM and their gaseous and electrochemical hydrogenation properties are studied to find out the effect of LM elements. Also, the second phase and initial activation performance are investigated. The Zr_1−xTi_xV_0.4Ni_1.2Mn_0.4LM_y (x=0.3,0.4; y=0.0,0.02,0.05,0.1,0.2,0.3) alloys have C14 Laves phase hexagonal structure, so the volume expansion ratio of lattice parameters with LM has increased. As the amount of LM in alloy has increased, correspondingly the second phase is also increased. The second phase is LM, Ti and V-rich. The second phase improve the activation of La-rich misch-metal, and also the concentration of elements Ti, V〉LM〉 matrix in alloys.The addition of LM in Zr_1−xTi_xV_0.4Ni_1.2Mn_0.4LM_y (x=0.3, 0.4) alloys have increased the activation rate and hydrogen storage capacity significantly, but the plateau pressure and the discharge capacity have been decreased due to the formation of second phase. For more Zr in electrode alloys, the activation of rate becomes slow.     

Effects of surface coating with polyaniline on electrochemical properties of La–Mg–Ni-based electrode alloys

The effects of surface coating with polyaniline on electrochemical properties of La_0.8Mg_0.2Ni_3.4Al_0.1 electrode alloys were studied in this paper. The flake-shaped polyaniline coatings were deposited on the surface of La_0.8Mg_0.2Ni_3.4Al_0.1 alloy powders by electrodeless deposition. Electrochemical studies showed that the discharge capacity increased to 391.8 mAh g⁻¹ after surface modification with polyaniline, compared to 382.5 mAh g⁻¹ for the bare alloys. The cyclic stability over 100 cycles improved from 81.6% to 87.5%. Also, the kinetic properties were investigated in detail.     

Formation and hydrogen storage properties of in situ prepared Mg–Cu alloy nanoparticles by arc discharge

Mg–Cu alloy nanoparticles were in situ prepared by a physical vapor condensation method (arc discharge) in a mixture of argon and hydrogen. Four crystalline phases, Mg, Mg₂Cu, MgCu₂ and MgO, were formed simultaneously during the arc-discharge evaporation. Detailed experiments revealed that nanostructured hydrogen-active phases of Mg₂Cu and Mg exhibit enhanced hydrogen absorption kinetics possibly due to the small grain size and surface defects. The maximal hydrogen storage contents of Mg–Cu alloy nanoparticles can reach 2.05 ± 0.10 wt% at 623 K.     

The preparation and properties of Mn–Co–O spinel coating for SOFC metallic interconnect

To meet the performance requirements of solid oxide fuel cell (SOFC) metallic interconnect, the Mn–Co–O spinel coating is prepared on the surface of AISI430 by pack cementation method to reduce the growth kinetics of oxides and inhibit the outward diffusion of Cr. The microstructural characterization shows that a dense, uniform, defect-free spinel coating is successfully fabricated on the surface of AISI430. Under the simulated SOFC cathode environment, the weight gain of coated steel (0.608 mg cm⁻²) after oxidation at 800 °C for 800 h is significantly lower than that of uncoated (1.586 mg cm⁻²). In addition, the area specific resistance (ASR) of the coated steel oxidized for 500 h is 17.69 mΩ cm², much smaller than that of the bare steel, indicating that the oxidation resistance and electrical conductivity of AISI430 are significantly improved by Mn–Co–O spinel coating. Cross-sectional observations of the Mn–Co–O spinel coating are conducted to assess the compatibility of substrate with the adjacent coating and its effectiveness in reducing the growth of the Cr₂O₃ layer.     

Conductivity percolation in carbon–carbon supercapacitor electrodes

Composite electrodes which comprise a non-conductive activated carbon of large surface area (1420 m² g⁻¹) and a conductive carbon black (CB) of small surface area (220 m² g⁻¹) have been prepared and studied for their capacitive properties in aqueous KOH and Na₂SO₄ electrolytes. For either electrolyte, maximum capacitance exists at the composition believed to correspond to the percolation threshold for CB, the conductive phase. At a CB content less than the threshold, the capacitance is limited mainly by the electronic resistance on the electrode side. The interfacial surface area becomes the limiting factor as the threshold is exceeded. A maximum capacitance of 108 F g⁻¹ at a voltage sweep rate of 20 mV s⁻¹ is obtained in 1 M KOH aqueous electrolyte with a CB content of 25 wt.% (or ∼14 vol.%).     

Image based modelling of stress–strain behaviour in carbon/carbon composites

Abstract

Numerical modelling is based on two fundamentals: first, developing a finite element (FE) mesh that represents faithfully the sample structure; and second, using reliable input data. In this paper, a methodology for creating image based FE meshes from X-ray microtomography (XMT) data sets of two 2D woven carbon–carbon composites (graphitised and ungraphitised) that are candidate materials for nuclear applications is described. Input data for the mechanical properties of the constituent phases are determined by nanoindentation. Compressive tests are also performed to generate experimental stress–strain curves to validate the predictions. The results showed good correlation between the experimental and numerically modelled stress–strain curves, therefore giving confidence in the approach. The stress distributions within the structure were also modelled. These showed the effect of pore shape on stress shielding. These predictions were also compared with simple analytical models for the structure. The image based models showed better agreement.     

Graphite–carbon nanotube composite electrodes for all vanadium redox flow battery

The voltammetric behaviors of graphite (GP) and its composites with carbon nanotube (CNT) were studied in 5 M H₂SO₄ + 1 M VOSO₄ solution with cyclic voltammetry (CV), and the surface morphology of the composites was observed with scanning electron microscope (SEM). The results obtained from voltammetry show that the redox couples of V(IV)/V(V) and V(II)/V(III), as positive and negative electrodes of all vanadium flow liquid battery, respectively, have good reversibility but low current on the GP electrode, and the current can be improved by CNT. It is found from the observation of SEM that the CNT is dispersed evenly on the surface of sheet GP when they are mixed together. The best composition for the positive and the negative of all vanadium flow liquid battery determined by comparing voltammetric behavior of the composite electrodes with different content of CNT is 5:95 (w_CNT/w_GP) for both positive and negative electrodes. The activity of the composite electrode can be affected by the heat treatment of CNT. CNT treated at 200 °C gives better activity to the composite electrode.     

Thermal stresses in a coating–substrate assembly caused by internal heat source

We determine two-dimensional temperature and thermal stresses distributions in a semiconductor coating-substrate assembly caused by the heat source at the contact surface. The analysis is based on the Laplace and Hankel integral transforms of equations of thermal elasticity, and the obtained analytical solutions can be used without any limitations on the duration of heating, the thickness of a coating, mechanical and thermal characteristics of materials. We consider the effect of the thickness of a coating, thermal mismatch between the substrate and the coating on the magnitude of thermal stresses. Using the obtained thermal stress distribution we analyze the delamination failure at the substrate-coating interface.     

Charge–discharge behaviour of VRLA batteries: model calibration and application for state estimation and failure detection

The dynamic behaviour of batteries can be predicted using theoretical cell model for basic processes. In this paper, this model is calibrated for two types of valve regulated lead acid (VRLA) batteries, and is applied for viewing unobservable processes in battery by observable processes. It is shown that unobservable parameters like overpotential, reaction rate, porosity, acid concentration, and other parameters of electrode can be evaluated by total current, terminal voltage and temperature of surrounding atmosphere of battery. The calibrated model is applied to distinguish between outwardly equal batteries with different backup time and cut-off time. It is shown that difference in morphology of electrodes, thickness of electrodes and quantity of electrolyte in separator are the main distinguishing parameters between batteries. These parameters can be tested online by current–voltage measurements using fast calculation method proposed in this paper.     

Hydrogen storage properties of Mg–Nb@C nanocomposite: Effects of Nb nanocatalyst and carbon nanoconfinement

The Mg–Nb@C nanocomposite has been synthesized by a reactive gas evaporation method to simultaneously achieve carbon nanoconfinement and add Nb nanocatalyst. The size of Mg particles is range from 14 to 26 nm with average size of 20 nm. The small Nb catalyst about 5 nm are decorated in Mg particles, and the proportion of Nb is about 8 wt%. The amorphous carbon layer with thickness of 2 nm is coated on the surface of Mg–Nb nanocomposite. The nanocomposite can absorb 6.4 wt% H₂ and desorb 6.3 wt% H₂ in 5 min at 673 K. At 573 K, it can also uptake 5.8 wt% H₂ in 10 min and release 4.8 wt% H₂ in 60 min. The E_a for hydrogenation and dehydrogenation are reduced to 60.2 and 59.7 kJ mol^?1, respectively. Carbon nanoconfinement and Nb nanocatalyst effectively improve the hydrogen sorption kinetic of Mg.     

Erosion–corrosion behaviour of Ni–20Cr plasma coating in actual boiler environment

Abstract

Erosion–corrosion is encountered in a large variety of engineering industries. In such environments, protective coatings are used. In this investigation, erosion–corrosion of the Ni–20Cr coating on nickel and iron based superalloys has been investigated by subjecting them to the boiler of coal fired thermal power plant at the temperature zone of 540°C for 1000 h duration. The erosion–corrosion kinetics of the plasma sprayed Ni–20Cr coating on different superalloys has been investigated. XRD, SEM with EDS and EPMA have been used to analyse the eroded–corroded products along the surface and cross-section. Main phases identified in all the Ni–20Cr coated superalloys after exposure are NiO, Cr₂O₃, Al₂O₃ and SiO₂. Aluminium has penetrated from the bond coat to the top coat along the splat boundaries. Oxides of chromium, nickel and aluminium are recognized as protective oxides for boiler environment. The probable mechanism of attack for Ni–20Cr coating in the given boiler environment is discussed.     

Emission analysis of the effect of carbon nanowires in biodiesel–ethanol blends

The present work is dedicated to study of diesel–biodiesel–ethanol blends in a diesel engine using addition of various concentrations of carbon nanowires. Algae oil from microalgae has the potential to become a sustainable fuel source as biodiesel. The Neochloris oleoabundans algal oil was extracted by mechanical extraction method. The transesterification reaction of algal oil with methanol and base catalyst was used for the production of biodiesel. Experimental investigation results were studied for various parameters, such as exhaust emission of carbon monoxide, hydrocarbon, oxides of nitrogen gases, smoke, and carbon dioxide.