Preparation and Thermal Properties of Graphene Oxide–Microencapsulated Phase Change Materials

In this article, the preparation of microencapsulated hexadecaol with graphene oxide (GO) shell was realized by Pickering emulsion templating. The microencapsulated phase change materials (MePCMs) were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) analysis, differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). The results showed that the MePCMs with 6 wt% GO had high thermal storage capabilities, excellent shape stability during phase change, and enhanced thermal stability due to the existence of a GO shell protecting the core material from leakage and evaporation. The research provides a novel composite PCM with GO for thermal energy storage.     

Phase change microcapsules with lead tungstate shell for gamma radiation shielding and thermal energy storage

Novel microencapsulated phase change materials (MEPCMs) composed of the lead tungstate (PbWO₄) shell and paraffin core were designed for shielding of gamma radiation as well as thermal energy storage. Such MEPCMs were prepared via self‐assembly methods and in‐situ precipitation. The PbWO₄ shell with excellent photon attenuation can give the resulting MEPCMs an acceptable gamma radiation shielding capability. The chemical composition and structure of microcapsules samples were studied by X‐ray diffractometer (XRD) and Fourier‐transform infrared spectroscopy (FTIR). The effects of different core/shell mass ratios on the surface morphology and microstructure of the MEPCMs were determined by scanning electron microscopy (SEM), energy‐dispersive spectrometer (EDS), and transmission electronic microscopy (TEM). It was confirmed that the microcapsules exhibit a distinct core‐shell structure and a perfect spherical shape. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to present thermal stability and thermal‐storage capability of MEPCMs. A high‐purity germanium gamma spectrometer to measure the attenuation coefficient of the microcapsules for gamma rays showed that the MECPMs has good γ‐rays‐shielding property. The multifunction microcapsules in this study have great potential applications for building energy conservation as well as wearable personal protection in nuclear energy engineering.     

TiO2–SiO2 mixed oxides: Organic ligand templated controlled deposition of titania and their photocatalytic activities for hydrogen production

A simple approach to the controlled deposition of titania with different particle sizes on silica surface has been developed by impregnation of an organic titania precursor followed by calcination. Among the several Ti-complexes tested, the templating effect of titanium phthalocyanine dichloride resulted in silica-supported titania with enhanced photocatalytic activity for photosplitting of water under UV light irradiation. The titania–silica materials were characterized by Powder X-ray diffraction (XRD), UV–Vis diffuse reflectance spectra (DRS), nitrogen adsorption studies, and Raman spectroscopic studies. The photocatalytic activity for hydrogen production is maximum at an optimal particle size wherein surface and volume recombination is minimized.     

Physicochemical properties of lithium iron phosphate‐carbon as lithium polymer battery cathodes

Lithium iron phosphate‐carbon (LiFePO₄/multiwalled carbon nanotubes (MWCNTs)) composite cathode materials were prepared by a hydrothermal method. In this study, we used MWCNTs as conductive additive. Poly (vinylidene fluoride‐co‐hexafluoropropylene)‐based solid polymer electrolyte (SPE) was applied. The structural and morphological performance of LiFePO₄/MWCNTs cathode materials was investigated by X‐ray diffraction and scanning electron microscopy/mapping. The electrochemical properties of Li/SPE/LiFePO₄‐MWCNTs coin‐type polymer batteries were analyzed by cyclic voltammetry, ac impedance and galvanostatic charge/discharge tests. Li/SPE/LiFePO₄‐MWCNTs polymer battery with 5 wt % MWCNTs demonstrates the highest discharge capacity and stable cyclability at room temperature. It is indicated that LiFePO₄‐MWCNTs can be used as the cathode materials for lithium polymer batteries. Copyright © 2011 John Wiley & Sons, Ltd.     

The micro‐/nano‐PCMs for thermal energy storage systems: A state of art review

With advancement in technology—nanotechnology, various thermal energy storage (TES) materials have been invented and modified with promising thermal transport properties. Solid‐liquid phase change materials (PCMs) have been extensively used as TES materials for various energy applications due to their highly favourable thermal properties. The class of PCMs, organic phase change materials (OPCMs), has more potential and advantages over inorganic phase change materials (IPCMs), having high phase change enthalpy. However, OPCMs possess low thermal conductivity as well as density and suffer leakage during the melting phase. The encapsulation technologies (ie, micro and nano) of PCMs, with organic and inorganic materials, have a tendency to enhance the thermal conductivity, effective heat transfer, and leakage issues as TES materials. The encapsulation of PCMs involves several technologies to develop at both micro and nano levels, called micro‐encapsulated PCMs (micro‐PCM) and nano‐encapsulated PCMs (nano‐PCM), respectively. This study covers a wide range of preparation methods, thermal and morphological characteristics, stability, applications, and future perspective of micro‐/nano‐PCMs as TES materials. The potential applications, such as solar‐to‐thermal and electrical‐to‐thermal conversions, thermal management, building, textile, foam, medical industry of micro‐ and nano‐PCMs, are reviewed critically. Finally, this review paper highlights the emerging future research paths of micro‐/nano‐PCMs for thermal energy storage.     

Characterization of equivalent series resistance of electric double-layer capacitor electrodes using transient analysis

In this study, transient equations based on chronoamperometry (CA), chronopotentiometry (CP), electrochemical impedance spectroscopy (EIS) and imaginary capacitance analysis (ICA) are proposed using two equivalent circuit models for the purpose of accurate estimation of the equivalent series resistance (ESR) in electric double-layer capacitor (EDLC) electrodes. After examining transient equations based on a simple resistance-capacitance series connection, alternative equations with a more complicated form are proposed using the transmission line model. From these equations, it is theoretically predicted that one-third of the electrolyte resistance within the pores contributes to the total ESR, irrespective of the electrochemical analysis method employed. As EDLC electrode materials, mesoporous carbons with different pore structure (size, surface area) are prepared by the direct template method. After fabrication of EDLC electrodes using these materials, transient experiments using CA, CP, EIS, and ICA are conducted, and a consistent ESR is obtained. From ESR comparison, it is observed that the increase in ESR is mostly attributable to the electrolytic resistance in the pores and is highly correlated with the pore structure of the carbon electrodes. Additionally, it is found that a mesoporous carbon electrode with a 2-h reaction time exhibits an improved rate performance comparable with that of ordered mesoporous carbon electrodes prepared by the templating of ordered mesoporous silica.     

Highly efficient hydrolysis of magnetic milled powder from waste aluminum (Al) cans with low‐concentrated alkaline solution for hydrogen generation

Currently, recycling waste aluminum materials are of significant importance for reducing environmental pollution and improving economic efficiency. In this paper, aluminum (Al) powder prepared from waste Al cans with magnetic grinding method was directly used in hydrolysis for hydrogen generation. The prepared waste Al cans powder was characterized by scanning electron microscope (SEM), X‐ray diffraction (XRD), Brunauer–Emmett–Teller (BET), atomic absorption spectrophotometer (AAS), and density analysis. The results showed that grinding time, NaOH concentration, and reaction temperature affected the hydrolysis rate and hydrogen yield markedly; 1 g of Al cans powder with grinding time of 40 minutes could produce 1296‐mL hydrogen within 6 minutes under the optimal reaction conditions. The reaction kinetics study demonstrated that the hydrolysis of Al cans powder is kinetically controlled while hydrolysis of Al cans flakes is diffusively controlled. The hydrolysis mechanism was also predicted based on the experimental results and kinetic study. The generation of hydrogen from hydrolysis of waste Al cans powder with low‐concentrated alkaline solution is a promising way to diminish environmental pollution and instrument corrosion.     

Radioluminescent nuclear battery containing CsPbBr3 quantum dots: Application of a novel wave‐shifting agent

Radioluminescent nuclear battery has been widely studied for its miniaturization and long life. In this study, all‐inorganic perovskite quantum dots (CsPbBr₃ QDs) were selected as a novel wave‐shifting agent combined with liquid scintillator PPO (2,5‐diphenyloxazole). The QDs were used to regulate the emission spectrum to match different GaAs devices. The maximum output power of the RL nuclear battery was greatly enhanced by 1.91 to 2.53 times. Perovskite QDs with adjustable emission spectra were used as wave‐shifting agents and exhibited more excellent properties and application prospects than traditional wave‐shifting agents. The Monte Carlo method was used to simulate the energy deposition of fluorescent materials under various radioactive source models. Results verified the advantages of using liquid radioactive sources and liquid fluorescent materials. The application and reference value of perovskite QDs in nuclear detection and nuclear medical imaging were also discussed.     

Sol-gel derived mixed phase (Mn,Ti)-oxides/graphene nanoplatelets for hybrid supercapacitors

In this investigation, (Mn, Ti)- oxides were prepared using pluronic 123 templating assisted sol-gel method. Sol-A with Ti precursor in ethanol was acidified with HCl whereas sol-B containing Mn precursor was prepared in ethanol containing 5 wt% pluronic 123 surfactant. Gelation was accomplished by the addition of de-ionized water. As-prepared gels were aged for 24 hours, dried at 80°C for 12 hours and calcined at 500°C to 1200°C for 5 hours to obtain powdered electrode materials, which were analyzed by x-ray diffraction, scanning electron microscopy/energy-dispersive x-ray, and Brunauer-Emmett-Teller (BET) surface area analysis. Hybrid supercapacitors were fabricated using the sol-gel derived (Mn, Ti)- oxides and Gr-nanoplatelets electrodes with aqueous KOH (potassium hydroxide) as electrolyte. Fabricated supercapacitors were charged with 2.0 V and 0.01 A for 10 minutes. Charged supercapacitors were tested via cyclic voltammetry to determine specific capacitance. For the powdered materials prepared with Mn:Ti at 65:35 wt% and calcined at 500°C, x-ray diffraction analysis revealed the presence of TiO₂-rutile, Mn₂O₃ and Mn₃O₄ as 20%, 60%, and 18%, respectively. At higher calcination temperature, TiO₂-rutile and Mn₂O₃ phases were found to be absent with the presence of higher perovskite (TiMnO₃) phase. Both pore volume and BET specific surface area was found to decrease with increase in calcination temperature. The specific capacitance was found be dependent on Mn:Ti wt% used to prepare the powdered materials as well as the calcination conditions. The gel prepared with Mn:Ti of 30:70 wt% followed by 2-step calcination yielded a maximum specific capacitance.     

Electrospun ultrafine composite fibers of binary fatty acid eutectics and polyethylene terephthalate as innovative form‐stable phase change materials for storage and retrieval of thermal energy

In this study, four fatty acids of lauric acid (LA), myristic acid (MA), palmitic acid (PA), and stearic acid (SA) were selected to prepare six binary fatty acid eutectics of LA‐MA, LA‐PA, LA‐SA, MA‐PA, MA‐SA, and PA‐SA; thereafter, electrospun ultrafine composite fibers with the binary fatty acid eutectics encapsulated in the supporting matrices of polyethylene terephthalate (PET) were prepared as innovative form‐stable phase change materials for storage and retrieval of thermal energy. The morphological structures and thermal energy storage properties of the ultrafine composite fibers were characterized by scanning electron microscope (SEM) and differential scanning calorimeter (DSC), respectively. The SEM results indicated that the fibers had the cylindrical morphology with diameters of 1–2 µm; some had smooth surfaces, while others had wrinkled surfaces with grooves. The DSC results indicated that the phase transition temperatures of binary fatty acid eutectics were lower than those of individual fatty acids; the enthalpy values associated with melting and crystallization for the eutectics encapsulated in the composite fibers were considerably reduced, whereas there were no appreciable changes on the phase transition temperatures. Copyright © 2012 John Wiley & Sons, Ltd.     

Compatibility of plastic with phase change materials (PCM)

Even though paraffin interactions with plastics are known by industry, plastics are commonly proposed as container materials for encapsulating phase change materials (PCM) in many applications. In the literature, there are very few experimental studies of organic PCM migration in plastics and its effects on plastic properties. These interactions are a case study of environmental stress cracking, which is considered one of the most common causes of plastic failure. The aim of this work is an experimental study of interactions of some PCM typically used for thermal energy storage, and some plastic materials currently used as encapsulating materials. With the materials tested in this work, it can be concluded that, for encapsulating organic PCM, low‐density polyethylene and polypropylene showed worse behaviour than high‐density polyethylene. Copyright © 2010 John Wiley & Sons, Ltd.     

Preparation of pentadecane/poly(melamine‐urea‐formaldehyde) microcapsules for thermal energy storage applications

Phase change materials (PCMs) with suitable melting ranges for thermal energy storage applications are alkanes, paraffins, fatty acids, eutectic mixtures, and inorganic PCMs. Paraffinic hydrocarbons and fatty acids with low solubility in water are usually the preferred candidates. Pentadecane, which is an alkane hydrocarbon with the chemical formula C₁₅H₃₂, was used as PCM in this study. The pentadecane was microencapsulated with a poly(melamine‐urea‐formaldehyde (MUF)) shell for thermal energy storage. Pentadecane/poly(MUF) microcapsules were prepared by in situ polymerization method. The morphological analysis of pentadecane microcapsules was analyzed with scanning electron microscopy (SEM). Thermal properties of microcapsulated pentadecane were determined by differential scanning calorimetry (DSC). The results demonstrated that pentadecane/PUF microcapsules were prepared successfully, and they offer proper phase transition temperature range (8.7°C and 8.1°C) and heat enthalpy values (84.5 and ?88.2 kJ/kg) for thermal energy storage applications. According to the results, it was determined that pentadecane/poly(MUF) microcapsules have good potential for thermal energy storage applications.     

Binary mixtures of fatty alcohols and fatty acid esters as novel solid‐liquid phase change materials

The discovery of new eutectic phase change materials (PCMs) will overcome the current PCM challenges such as nonbiodegradability, super‐cooling, and limited thermal stability. This paper reports on the development of new bio‐based PCMs composed of binary mixtures of fatty acid esters and fatty alcohols at their eutectic compositions, which provide potential solid‐liquid PCMs for building applications. Six binary systems, namely 1‐dodecanol (DD) + methyl stearate (MES), DD + methyl palmitate (MEP), DD + methyl laurate (MEL), 1‐tetradecanol (TD) + MES, TD + MEP, and TD + MEL were prepared and their thermal behaviours were deliberated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), long‐term thermal stability test, and mass loss analysis. Amongst the studied systems, phase change transition temperature and latent heat of fusion of the eutectic mixtures of DD‐MES, DD‐MEP, TD‐MES, and TD‐MEP were found to be suitable for the building application with values of 22.46°C/201.91 J/g, 20.34°C/224.45 J/g, 32.05°C/209.38 J/g, and 26.72°C/210.15 J/g, respectively. The average degree of super‐cooling for all PCMs was below 2°C, and no significant changes in thermophysical properties of the developed PCMs were observed after 1000 thermal cycles.     

Evaluation of efficiency factors and internal resistance of thermoelectric materials

It is well known that the figure of merit (ZT) is unreliable in calculating the efficiency (?) of micro thermoelectric generators system level and unrealistic when comparing the performance of thermoelectric (TE) materials in the same metric units. To solve this problem, we have used COMSOL multiphysics to design a single leg of micro thermoelectric generators model for computing efficiency factors (? ) and internal resistance using TE materials' constants, such as electrical conductivity (σ ), TE conductivity (K ), and Seebeck coefficient (α ). The TE materials were placed between two copper electrodes, and the first data analyzed were the voltages per meter and electric currents per meter. The internal resistances were calculated by taking the ration of voltages to electric currents, and at the same time, the electric powers were calculated from the products of electric currents and voltages yielding power per unit area in μW cm^?2. The ? were calculated using changes in power (ΔP ), temperature gradient (ΔT ), and the surface area (A ). The obtained results showed that the TE materials with highest ? when the temperatures are between 375 and 550 K are n‐type SiGe and p‐type SiGe. When the temperatures are between 550 and 780 K, the TE materials with the highest ? are PbTe‐Pbl₂, PbTe‐CdTe, and PbTe‐SrTe‐Na. We noted that the ? obtained from eight TE materials in this work are within the range as those reported in the literature between 0.001 and 0.091 μW cm^?2 K^?2. The TE materials with high internal resistances such as PbS, PbTe, and PbSe have ? that is <0.0001 μW cm^?2 K^?2, and those with low internal resistances have ? in the range between 0.002 and 0.0091 μW cm^?2 K^?2. This work has shown that COMSOL multiphysics is a powerful computational tool that can be used to analyze internal resistances and ? of TE materials in the same temperature ranges. Copyright © 2016 John Wiley & Sons, Ltd.     

Designing behenic acid microcapsules as novel phase change material for thermal energy storage applications at medium temperature

Fatty acids are bio-based materials that can be used as phase change materials (PCMs). Microencapsulation of low carbon number fatty acids for mainly building applications have been realized in previous studies. In this study, behenic acid (BA), a fatty acid with medium melting range (65°C-85°C), has been microencapsulated for the first time. PMMA and its three copolymers were used as shell material of these novel encapsulated PCMs prepared by emulsion polymerization technique. The influences of using different comonomers in shell materials on the thermal, morphological, and chemical properties were investigated. Melting phase change temperature ranges were found as 65°C to 85°C for all capsule candidates. Capsules had uniform spherical geometry with size ranges under 500 nm. The capsules are suggested as novel PCM candidates in this temperature range that has potential applications in industrial waste heat, electronics, solar residential heating, lithium-ion batteries, and automotive application.     

Comparison of different methods for the determination of moisture content in biomass

The purpose of this study was to compare different methods for the determination of moisture in biomass. Twenty different biomass materials from various places in Europe were investigated for total moisture using oven drying in air at three different temperatures (80, 105 and 130 °C), distillation with xylene, and freeze drying. In addition, the materials were used for the comparison of different methods for the determination of moisture in the analysis sample. In all cases CEN TC335 Solid Biofuels—Methods for determination of moisture content—Oven dry method was used as the reference method. Significant differences were obtained between the oven-drying methods in air at various temperatures. Similar results were found for some materials when comparing the reference method with xylene distillation and freeze-drying methods. In some cases the discrepancies were explained by the loss of volatile organic compounds during the oven-drying step at elevated temperatures. Small differences were found in the comparison of methods for the determination of moisture in the analysis sample.     

Evaluating the environmental impacts of recycling wind turbines

Wind power is one of the fastest growing renewable energy sources. The wind turbines have an expected design lifetime in the range of 20 to 25 years after which decommissioning is expected. The trend in the wind turbine industry is that the turbines increase in size—especially when considering offshore wind turbines in the 7 to 8 MW size range. Life cycle assessments show that the materials used for manufacturing the turbines accounts for 70 to 80% of the environmental impact, so ensuring optimal recycling at the end‐of‐service‐life is of economic and environmental interest and in line with the principles of transitioning towards a circular economy. The decommissioning and recycling process is analysed in this paper, with special considerations given to the environmental aspects of a theoretical 100% recyclability scenario. This includes cradle‐to‐gate life‐cycle inventory analysis of the materials, embedded energy, and CO₂‐equivalent emissions. The findings show that established recycling methods are present for most of the materials and that recycling of a 60 MW wind park at end‐of‐service‐life provides environmental benefits as well as lowering the natural resource use and securing resources for use in the future. The saved energy is estimated to approximately 81 TJ. The reduction in emissions related to the recycling of wind turbine material totals approximately 7351 ton CO₂.     

Fabrication of the hydrogen-evolving photocatalyst with mesoporous structure

The photocatalyst TiO₂ with a wormhole-like mesoporous structure and narrow pore distribution were successfully synthesized using triethanolamine as template. The complex oxides InVO₄ with a relatively high surface area, a visible light active hydrogen-evolving photocatalyst, were obtained by means of the templating hydrothermal method with a variety of surfactants. InVO₄ with wormhole-like structure were fabricated by templating of cetyltrimethylammonium bromide. By comparing with the non-mesoporous samples, the mesoporous photocatalysts exhibited higher photocatlytic hydrogen evolution activity for water splitting in the absence and in the presence of oxalic acid.     

In situ self‐template synthesis of cobalt/nitrogen‐doped nanocarbons with controllable shapes for oxygen reduction reaction and supercapacitors

Shape‐controlled Co/N‐doped nanocarbons derived from polyacrylonitrile (PAN) were synthesized by a one‐step in situ self‐template method followed by a pyrolysis procedure. This is the first study to tune the nanostructure of Co/N‐doped carbon materials by providing a metal salt as the template and additive. The moderate surface area (699.47 m² g^?1), highly developed pore structure, homogenous Co and N doping and designed “egg‐box” structure impart Co/N‐doped cross‐linked porous carbon (Co/N‐CLPC) with excellent electrocatalytic activity and capacitive performance. This material displayed an onset potential of 0.805 V (vs RHE), a current density of ?5.102 mA cm^?2, excellent long‐term durability, and good resistance to methanol crossover, which are comparable with the characteristics of a commercial 20‐wt% Pt/C catalyst. In addition, Co/N‐CLPC demonstrated a high specific capacitance of 313 F g^?1 at 0.5 A g^?1, notable rate performance of 63% at 50 A g^?1, and good cycling stability of 104.8% retention after 5000 cycles when used as a supercapacitor electrode. This method enables new routes to obtaining Co/N‐doped nanocarbons with shape‐controlled structures for energy conversion and storage applications.