Thermal diffusivity study of aged Li-ion batteries using flash method

Advanced Li-ion batteries with high energy and power density are fast approaching compatibility with automotive demands. While the mechanism of operation of these batteries is well understood, the aging mechanisms are still under investigation. Investigation of aging mechanisms in Li-ion batteries becomes very challenging, as aging does not occur due to a single process, but because of multiple physical processes occurring at the same time in a cascading manner. As the current characterization techniques such as Raman spectroscopy, X-ray diffraction, and atomic force microscopy are used independent of each other they do not provide a comprehensive understanding of material degradation at different length (nm² to m²) scales. Thus to relate the damage mechanisms of the cathode at mm length scale to micro/nanoscale, data at an intermediate length scale is needed. As such, we demonstrate here the use of thermal diffusivity analysis by flash method to bridge the gap between different length scales. In this paper we present the thermal diffusivity analysis of an unaged and aged cell. Thermal diffusivity analysis maps the damage to the cathode samples at millimeter scale lengths. Based on these maps we also propose a mechanism leading to the increase of the thermal diffusivity as the cells are aged.     

KW-GO,a graphene-like carbon extracted from kitchen waste (KW) advances the hydrogen production of V2O5

In this paper, graphene-like carbon (KW-GO) extracted from kitchen waste (KW) is used to reduce the agglomeration of V₂O₅ and improve the separation rate of photogenerated electron-hole pairs from V₂O₅. We found that the V₂O₅-KW-GO composite material (VKW-GO) could significantly enhance the photocatalytic activity and H₂ production rate under visible light irradiation compared to pure V₂O₅. To analyze the composition and morphology of the materials, XRD, SEM, BET, UV–Vis, XPS, and Raman were measured. The results showed that the addition of KW-GO reduced the aggregation of V₂O₅ powder. At the same time, the specific surface area of the composite sample increased providing more active sites for photocatalytic hydrogen production. In addition, the visible absorption range of the composite sample also increased. As a result, the hydrogen production rate of V₂O₅ increased from 247.52 mol h^?1 g^?1 to 354.15 mol h^?1 g^?1. The method using V₂O₅ and VKW-GO as a catalyst for H₂ production is innovative, and the conclusion may provide important theoretical guidance for photocatalytic hydrogen production.     

Damage-free reactive ion etch for high-efficiency large-area multi-crystalline silicon solar cells

Texturing of silicon (Si) wafer surface is a key to enhance light absorption and improve the solar cell performance. While alkaline texturing of single-crystalline Si (sc-Si) wafers was well established, no chemical solution has been successfully developed for multi-crystalline Si (mc-Si) wafers. Reactive-ion-etch (RIE) is a promising technique for effective texturing of both sc-Si and mc-Si wafers, regardless of crystallographic characteristics, and more suitable for thin wafers. However, due to the use of plasma source generated by high power, the wafer surface gets a physical damage during the processing, which requires an additional subsequent damage-removal wet processing. In this work, we developed a damage-free RIE texturing for mc-Si solar cells. An improved self-masking RIE texturing process, developed in this study, produced ∼0.7% absolute efficiency gain on 156×156 mm² mc-Si cells, where the gas ratio and the plasma power density were keys to mitigate the plasma-induced-damage during the RIE processing while maintaining decent surface reflectance. In the self-masking RIE texturing, a mixture of SF₆/Cl₂/O₂ gases was found to significantly affect the surface morphology uniformity and reflectance, where an optimal etch depth was found to be 200-400 nm. We achieved J_sc gain of ∼1.3 mA/cm² while maintaining decent FFs of ∼0.78 without a V_oc loss after optimization of firing conditions.     

Effect of corrosion inhibitors on hydrogen uptake by Al from NaOH solution

Corrosion rate, hydrogen permeation rate (hydrogen uptake) and stress corrosion cracking of Al were studied in NaOH solutions, pure and with the addition of H₃BO₃, EDTA, KMnO₄ and As₂O₃. The presence of the studied species in electrolyte and the implantation of Al surface with B⁺ ions inhibited corrosion. Hydrogen uptake was found to be promoted or inhibited by means of studied species, depending on the method of their introduction into the base solution and on the applied polarization. The observed different influence of corrosion inhibitors on the hydrogen uptake was associated with the different chemical composition and structure (revealed by XPS analysis) of the surface films, formed on Al under the various conditions. Under similar polarization conditions, the presence of H₃BO₃ in the base solution similarly affected the hydrogen uptake by Al and the susceptibility to stress corrosion cracking of the metal.     

Reactivity investigation on chemical looping gasification of biomass char using nickel ferrite oxygen carrier

Chemical looping gasification (CLG) involves the use of an oxygen carrier (OC) which transfers oxygen from air to solid fuel to convert the fuel into synthesis gas, and the traditional gasifying agents such as oxygen-enriched air or high temperature steam are avoided. In order to improve the reactivity of OC with biomass char, facilitating biomass high-efficiency conversion, a compound Fe/Ni bimetallic oxide (NiFe₂O₄) was used as an OC in the present work. Effect of OC content and oxygen sources on char gasification were firstly investigated through a TG reactor. When the OC content in mixture sample attains 65 wt.%, the sample shows the maximum weight loss rate at relatively low temperature, indicating that it is very favorable for the redox reactions between OC and biomass char. The NiFe₂O₄ OC exhibits a good performance for char gasification, which is obvious higher than that of individual Fe₂O₃ OC and mechanically mixed Fe₂O₃ + NiO OC due to the Fe/Ni synergistic effect in unique spinel structure. According to the TGA experimental results, effect of the steam content and cyclic numbers on char gasification were investigated in a fixed bed reactor. Either too low steam content or too high steam content doesn't facilitate the char gasification. And suitable steam content of 56.33% is determined with maximum carbon conversion of 88.12% and synthesis gas yield of 2.58 L/g char. The reactivity of NiFe₂O₄ OC particles shows a downtrend within 20 cycles (～64 h) due to the formation of Fe₂O₃ phase, which is derived from the iron element divorced from the Fe/Ni spinel structure. Secondly, the sintering of OC particles and ash deposit on the surface are also the reasons for the deactivation of NiFe₂O₄ OC. However, the carbon conversion and synthesis gas yield at the 20th cycle are still higher than those of the blank experiment. It indicates that the reactivity of NiFe₂O₄ OC can be maintained at a relatively long time and NiFe₂O₄ material can be used as a good OC candidate for char gasification in the long time running.     

Unprecedented solar water splitting of dendritic nanostructured Bi2O3 films by combined oxygen vacancy formation and Na2MoO4 doping

We demonstrate the synergetic effect of Na₂MoO₄-doping and vacuum-annealing on dendritic nanostructured bismuth oxide (Bi₂O₃) thin films prepared by electrodeposition for visible-light-assisted photoelectrochemical (PEC) water oxidation. After evaluating various extents of Na₂MoO₄-doping as well as vacuum-annealing temperatures, it was evidenced that both Na₂MoO₄-doping and vacuum-annealing significantly improved the efficiency and PEC water oxidation performance. Compared to the undoped Bi₂O₃ photoanode, the optimized Na₂MoO₄-doped Bi₂O₃, after vacuum-annealing, resulted in more than 25-fold enhancement in the photoanodic current density to 1.06 mA/cm² at 1.23 V_RHE under AM1.5 G illumination. The PEC enhancement is credited mainly to the increased PEC surface active sites in the Na₂MoO₄-doped vacuum annealed sample. Confirmed by combined XPS and Mott-Schottky (M ? S) analysis, vacuum annealing resulted in surface oxygen vacancies that can contribute to the photocatalytic activity. Besides, Na₂MoO₄-doping resulted in reduced dimensions of the dendritic structure, revealed by FE-SEM and XRD measurements, resulting in larger surface area and, therefore, larger surface/electrolyte contact. This dual strategy (metal doping + vacuum annealing) can be generalized to assemble photoanodes of other materials used for the production of solar fuels. Our results make a valuable step towards efficient Bi₂O₃/BiVO₄ pn heterojunctions.     

Two dimensional Cu based nanocomposite materials for direct urea fuel cell

In this work, Cu₂O nanoparticles were successfully prepared onto the surface of two-dimensional graphitic carbon nitride (g-C₃N₄) by using a simple solution chemistry approach. An environment-friendly reducing agent, glucose, was used for the synthesis of Cu₂O NPs onto the surface of g-C₃N₄ without using any surfactant or additives. The surface composition, crystalline structure, morphology, as well as other properties have been investigated using XPS, XRD, SEM, FTIR, FESEM, EDS, etc. The electrochemical measurements of the prepared materials demonstrated that Cu₂O exhibited a weak oxidation activity towards urea, while g-C₃N₄ has no activity towards urea oxidation. The Cu₂O supported on the surface of g-C₃N₄ (Cu₂O-g-C₃N₄) demonstrated a significant activity towards urea oxidation that reached two times that of the unsupported one. The significant increase in the performance was related to the synergetic effect between the Cu₂O and g-C₃N₄ support. The prepared composite materials demonstrated high stability towards urea oxidation as confirmed from the stable current discharge for around 3 h without any noticeable degradation performance.     

Impulse voltage withstand capability of rotating machine insulationas determined from model specimens

An evaluation of present-day turn and groundwall insulation is discussed. The surge breakdown voltage of unaged insulated specimens was evaluated at two rates of surge voltage rise; the values of breakdown voltage were compared to those obtained by direct voltage and 60 Hz alternating voltage. The insulations were then aged by voltage from conductor to ground and periodically evaluated for surge breakdown values. Finally, the specimens were tested for surge voltage endurance, and this endurance was compared to alternating voltage endurance     

Optimization for hydrogen production from methanol partial oxidation over Ni–Cu/Al2O3 catalyst under sprays

In this work, a novel Ni–Cu/Al₂O₃ catalyst is used to trigger the partial oxidation of methanol (POM) for hydrogen production. This reaction system also employed ultrasonic sprays to aid in dispersing methanol fuel. The prepared catalyst is analyzed by scanning electron microscope (SEM), energy-dispersive X-ray (EDX) spectroscopy, and X-ray diffraction (XRD) to explore the catalyst's surface structure, elemental composition, and physical structure, respectively. The Box-Behnken design (BBD) of response surface methodology (RSM) is utilized for experimental design to achieve process optimization. The operating parameters comprise the O₂/C molar ratio (0.5–0.7), preheating temperature (150–250 °C), and weight percent (wt%) of Ni (10–30%) in the catalyst. The results show that methanol conversion is 100% in all the operating conditions, while the reaction temperature for H₂ production ranges from 160 to 750 °C, stemming from heat released by POM. The significance and suitability of operating conditions are also analyzed by analysis of variance (ANOVA). It indicates that the highest H₂ yield is 2 mol (mol CH₃OH)^?1, occurring at O₂/C = 0.5, preheating temperature = 150 °C, and Ni wt% = 10. Compared with the commercial h-BN-Pt/Al₂O₃ catalyst, the prepared Ni–Cu/Al₂O₃ catalysts have higher activity for H₂ production. The O₂/C ratio is the most influential factor in the H₂ yield. Moreover, the interaction of the O₂/C ratio and Ni content is sound, reflecting that changing Ni content in the catalyst will affect the trend of H₂ yield under each O₂/C.     

Degradation of turn insulation in motor coils under repetitivesurges

Degradation of interturn insulation caused by repetitive surges is studied for coils in three motors stators. In each stator, the coils are isolated and divided into several groups. Breakdown voltages of coils in one group are measured for 0.1 μs risetime impulses and the average breakdown voltage of these unaged coils is determined. Coils in the other groups are first subjected to a number (1000 to 8000) of surges with magnitudes of 3.0 to 7.8 pu, and then the impulse breakdown voltages for these aged coils are measured and compared with those for the unaged coils. The results of the measurements on two stators showed no evidence of degradation of turn insulation by surges. There is an indication of surge aging of the turn insulation for one stator. Surge magnitudes capable of causing detectable aging of turn insulation appear to be higher than those likely to occur at normally operating utility motors. The existence of a threshold value of surge magnitude required to produce aging effects is a possible hypothesis     

High-density plasma nitriding of AISI 316L for bipolar plate in proton exchange membrane fuel cell

Austenitic stainless steel (AISI 316L) is nitrided by inductively coupled plasma using a gas mixture of N₂ and H₂ at temperatures between 530 K and 650 K, and the corrosion resistance as well as the interfacial contact resistance (ICR) are measured in a simulated proton exchange membrane fuel cell (PEMFC) environment.After plasma nitriding, a nitrogen-expanded austenite layer, the so-called S-phase is formed in all nitrided samples. The ICR value of the nitrided samples decreases to approximately 10 mΩcm² after plasma nitriding. The sample nitrided at 590 K shows the best corrosion property, while the corrosion resistance of the sample nitrided at higher temperatures decreases because of the formation of Cr-depleted regions in the nitrided sample. By using high-density plasma, the process temperature can be reduced to such a low temperature that Cr depletion is not significant, but a dense S-phase is formed.     

Cobalt-doped layered lithium nickel oxide as a three-in-one electrode for lithium-ion and sodium-ion batteries and supercapacitor applications

Layered LiNi_0.94Co_0.06O₂ (LNCO) was prepared and explored as an energy-storage material for Li-ion (LIBs), Na-ion (SIBs) batteries as well as supercapacitor application for the first time. All the physical and morphological characterizations were studied for the sample LNCO. The result displays good thermal stability, phase purity in the crystal structure, appreciable Brunauer-Emmett-Teller (BET) surface area (5.53 m² g⁻¹) and possesses cubic morphology. The cobalt was identified in lithium nickel oxide with binding energies at 794.02, 779.04 and 784.30 eV, respectively. In the case of LIBs, LNCO exists with a minimal difference of 5 mAh g⁻¹, even when cycled from 2C to 0.1C. After 200 cycles, the specific capacity, 247 mAh g⁻¹, is obtained for the cell with retention of 97.8% (efficiency 99.8%) at 0.1C. In SIBs, at 0.1C, the discharge capacity of 182 mAh g⁻¹ was restored even when cycled after 2C. After 200 cycles, a discharge capacity of 204 mAh g⁻¹ is ensured with retention of 96.6% (efficiency of 99.4% at 0.1C). In supercapacitor, the electrode, LNCO, delivered a specific capacity of 300 F g⁻¹ at 0.5 A g⁻¹. Therefore, LNCO is highly recommended as a suitable electrode material for fulfilling the requirement of energy-storage applications.     

The fracture properties of aged 316 austenitic steel

The fracture properties of 316 austenitic steel aged at 700°C are assessed in this paper. Charpy impact energy, crack growth fracture resistance, J-Δa, and tensile properties were compared with the unaged properties at four different ageing times. The J-Δa curves were measured from pre-cracked Charpy and 25 mm compact specimens using the unloading compliance technique.

The degradation in fracture properties with ageing is explained in terms of the microstructural behaviour of the steel.     

Activation of TiFe for hydrogen storage by plastic deformation using groove rolling and high-pressure torsion: Similarities and differences

Intermetallics of TiFe were processed using three different routes: annealing, plastic deformation using groove rolling and severe plastic deformation using high-pressure torsion (HPT). Hydrogen absorption was less than 0.2 wt.% in the coarse-grained annealed sample because of difficult activation. The groove-rolled sample, with subgrain structure and high density of dislocations and cracks, absorbed 0.3, 1.0, 1.4 and 1.7 wt.% of hydrogen in the first, second, third and fourth hydrogenation cycles, respectively. The HPT-processed sample, containing nanograins, absorbed 1.7–2 wt.% of hydrogen in any hydrogenation cycles. Both samples activated by groove rolling and HPT were not deactivated by long time exposure to the air. No surface segregation was detected after groove rolling, while the HPT-processed sample exhibited surface segregation. The current study confirmed the significance of plastic deformation and formation of grain boundaries and cracks on activation for hydrogen storage.     

Effects of MWCNTs on improving the hydrogen storage performance of the Li3N system

In this paper, the influence of multi-walled carbon nanotube (MWCNT)-doping on the hydrogen storage properties of the Li₃N system was systematically investigated. Compared with the pure Li₃N sample, the MWCNT-doped Li₃N sample shows faster hydrogen absorption and desorption kinetics and a drastically improved cycling stability. Along with increasing MWCNT content, the hydrogen storage improvement becomes more apparent. When the MWCNT doping level reaches 10 mol%, the enhancement effect is significant. The improved hydrogen storage properties of the Li₃N system by MWCNT-doping can be reduced to the physical effect of ball milling, the increased specific surface area and large pores as well as the good thermal conductivity of MWCNTs.     

Enhancement of electrochemical properties of Pd/C catalysts toward ethanol oxidation reaction in alkaline solution through Ni and Au alloying

The effect of Au and/or Ni addition on the ethanol oxidation reaction (EOR) performance in alkaline media of Pd-based binary and ternary catalysts (Pd₃Au/C, Pd₃Ni/C, and Pd₃AuNi/C) is systematically elucidated. The EOR activities, structures, morphologies, surface compositions and surface species of the prepared catalysts are analyzed by cyclic voltammetry, X-ray diffraction and X-ray absorption spectroscopy, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and temperature-programmed reduction, respectively. It is observed that the surface Ni with the chemical state of NiOOH can promote the EOR through bi-functional mechanism and spillover while surface Au can modify the Pd lattice and electron configuration which is helpful for the absorption of ethanol molecular. Chronoamperometric (CA) results obtained at room temperature demonstrate that the mass current density of ternary Pd₃AuNi/C catalysts after the long-term EOR test for 4 h is about 1.39 and 1.10 times higher than that of the monometallic Pd/C and binary Pd₃Au/C catalysts, respectively. It is proposed that the EOR stability enhancement of Pd₃AuNi can be attributed to the synergistic effect of Ni and Au alloying.     

Interaction of H2S with perfect and S-covered Ni(110) surface: A first-principles study

First-Principles study based on Density functional theory (DFT) calculations are employed to investigate the dissociative mechanism of H₂S adsorption and its dissociation on perfect, and sulfur covered Ni(110) surface. On both surfaces, we probe the site preference for H₂S, HS, H, and S adsorption mechanisms. The results indicate that H₂S is energetically adsorbed on their high symmetry adsorption sites with the preferred short-bridge (SB) site on both surfaces. Furthermore, we found that chemisorption of HS is stronger in contrast to H₂S at favorable short-bridge (SB) with a binding energy of −3.59 eV on perfect Ni(110) surface, and on S-covered Ni(110) surface at the favorable hollow site having a binding energy of −3.57 eV. In the first H₂S dehydrogenation, energy barriers for S–H bond breaking over the clean surface are 0.08–0.46 eV and a little bit higher on the S-covered surface are 0.1–0.78 eV, while in second dehydrogenation the energy barrier on a clean surface is 0.19 eV. For further detail, electronic densities of states and d-band center model are used to characterize the interaction of adsorbed H₂S with both surfaces. Hence, our results show that decomposition of H₂S over perfect and S-covered Ni(110) surface is exothermic and also an easy process. However, kinetically and thermodynamically, the subsistence of surface sulfur avoids the H–S bond breaking process.     

Poly-Si thin films by metal-induced growth for photovoltaic applications

Poly-Si films were produced using a metal-induced growth technique by sputtering from an n-type Si target onto a 50 nm thick Co seed-layer at 625°C. Silicon grew heteroepitaxially on the CoSi₂ layer formed due to the reaction between the sputtered Si atoms and Co at the beginning stage of deposition. A 5 μm thick Si film with grain features up to 1 μm was produced on the thin and flexible tungsten substrate by using a two-step sputtering method. The films also have a natural texture structure on the surface that is strongly recommended in thin-film solar cells in order to obtain high current density by increasing incident light trapping. After post-sputtering annealing at 700°C, the measured minority carrier lifetime for poly-Si film was 1.33 μs which shows the film to be suitable for photovoltaic applications. To explore the photovoltaic applications by using MIG poly-Si films, Au/n-Si Schottky photodiodes were fabricated due to the process simplicity. The effects of different parameters, which include film doping density, active-layer thickness, Si film surface conditions and hydrogenation, were studied. It was found that with the increasing of doping density, the open-circuit voltage (V_oc) increased while short-circuit current density (J_sc) decreased. Increasing the poly-Si active-layer thickness tended to improve the light absorption with an increased J_sc, but the V_oc was decreased due to a higher value of reverse saturation current. Because the metal/semiconductor interface condition facilitates the carrier transport in Schottky devices, the earlier study of modifying the Si surface by polishing showed an improved V_oc. The overall photo response was further improved by plasma hydrogenation.     

Cobalt decorated graphitic carbon nitride photoanode for electrochemical ethanol oxidation: A sustainable way towards clean energy

Energy conversion devices based on liquid fuels have gained considerable attention in recent times to meet the increasing global demand for energy. In this work, graphitic carbon nitride (gCN) nanosheets have been synthesized by pyrolysis of urea and Co has been decorated in different molar ratios over its surface by the solution phase method. The prepared catalysts have been utilized for photo electrooxidation of ethanol, an anodic half-cell reaction in direct ethanol fuel cells. Electrochemical studies show that the catalyst containing 3 mol % of Co shows the best activity with a peak current density of 6.91 mA/cm² obtained at a peak potential of 0.28 V with maximum current density of 40 mA/cm². The effect of light on the catalytic activity has also been studied. On illuminating the surface of the electrode with light, an increment of 85% in current density is observed which indicates higher charge transfer that enhanced the photoactivity of the catalyst. This study confirms the practical applicability of the non-expensive carbonaceous material Co–C₃N₄ utilization as a photoanode in future energy systems.     

Microstructural details of hydrogen diffusion and storage in Ti–V–Cr alloys activated through surface and bulk severe plastic deformation

Structural observations were carried out on particles obtained after hydrogenation cycling of the Ti₂₅V₅₀Cr₂₅ and Ti₁₀V₇₅Cr₁₅ alloys processed by surface or bulk severe plastic deformation using the surface mechanical attrition treatment (SMAT) and high-pressure torsion (HPT) techniques, respectively. The produced particles differ in morphologies and fracture mode due to the differences in hydrogen diffusion paths. The fracture mode for the SMAT-processed samples with the gradient microstructure was mainly intragranular, whereas it was intergranular for the nanograined HPT processed samples. Hydrogen diffusion, which initiated at the grain boundaries on the surface, created Ti-rich and V-lean areas. The powders contained mainly β-VH monohydride and partly γ-VH₂ dihydride, and an orientation relationship of (100)_β//(110)_γ and [001]_β//[001]_γ with an angular deviation of ∼2.5° was observed between the two phases using the electron backscattered diffraction (EBSD) analysis.