Peerapan Dittanet

Charge storage mechanisms of electrospun Mn3O4 nanofibres for high-performance supercapacitors

Mixed oxidation states of manganese oxides are widely used as the electrodes in supercapacitors due to their high theoretical pseudocapacitances. However, their charge storage mechanisms are not yet fully understood. In this work, the charge storage mechanism of Mn3O4 or Mn2+(Mn3+)2O4 nanofibres was investigated using a synchrotron-based X-ray absorption spectroscopy (XAS) technique and an in situ electrochemical quartz crystal microbalance (EQCM). The average oxidation state of the Mn in the as-synthesized Mn3O4 is +2.67. After the first charge, the average oxidation states of Mn at the positive and negative electrodes are +2.61 and +2.38, respectively. The significant change in the oxidation state of Mn at the negative electrode is due to phase transformation of Mn3O4 to NaδMnOx·nH2O. Meanwhile, the charge storage mechanism at the positive electrode mainly involves the adsorption of counter ions or solvated SO42−. After the first discharge, the calculated Mn average oxidation numbers are +2.51 and +2.53 at the positive and negative electrodes, respectively. At the negative electrode, the solvated Na+ is desorbed from the electrode surface. At the same time, the solvated SO42− is desorbed from the positive electrode. The mass change of solvated Na+ during charging/discharging is ca. 80 ng per cm2 of the Mn3O4 electrode. A symmetric supercapacitor constructed from Mn3O4 nanofibres in 0.5 M Na2SO4 provides a working potential of 1.8 V, a specific energy of 37.4 W h kg−1 and a maximum specific power of 11.1 kW kg−1 with 98% capacity retention over 4500 cycles. The understanding of the charge storage mechanism of the mixed oxidation states of Mn2+(Mn3+)2O4 presented in this work could lead to further development of metal oxide-based pseudocapacitors.

Hybrid Energy Storage of Ni(OH) 2 -coated N-doped Graphene Aerogel//N-doped Graphene Aerogel for the Replacement of NiCd and NiMH Batteries

Although Nickel–Cadmium (NiCd) and Nickel–metal hydride (NiMH) batteries have been widely used, their drawbacks including toxic Cd and expensive La alloy at the negative electrodes, low energy density (40–60 Wh/kg for NiCd and 140–300 Wh/L for NiMH), low power density (150 W/kg for NiCd and 1000 W/kg for NiMH), and low working potential (1.2 V) limit their applications. In this work, Cd and La alloy were replaced with N-doped reduced graphene oxide aerogel (N-rGOae) providing a hybrid energy storage (HES) having the battery and supercapacitor effects. The HES of Ni(OH)2-coated N-rGOae//N-rGOae provides 1.5 V, a specific energy of 146 Wh/kg, a maximum specific power of 7705 W/kg, and high capacity retention over 84.6% after 5000 cycles. The mass change at the positive electrode during charging/discharging is 8.5 µg cm−2 owing to the insertion/desertion of solvated OH− into the α-Ni(OH)2-coated N-rGOae. At the negative electrode, the mass change of the solvated K+, physically adsorbed/desorbed to the N-rGOae, is 7.5 μg cm−2. In situ X-ray absorption spectroscopy (XAS) shows highly reversible redox reaction of α-Ni(OH)2. The as-fabricated device without using toxic Cd and expensive La alloy has a potential as a candidate of NiCd and NiMH.

Hybrid energy storage of battery-type nickel hydroxide and supercapacitor-type graphene: redox additive and charge storage mechanism

Herein, hybrid energy storages (HESs) of battery-type Ni(OH)2 and supercapacitor-type electrochemically reduced graphene oxide (ERGO) were fabricated using potassium ferricyanide (K3Fe(CN)6) as a redox additive in KOH electrolyte for high specific energy and power applications. The as-fabricated HES of Ni(OH)2//ERGO in a single coin cell (CR2016) size in 4 mM K3[Fe(CN)]6 in 1 M KOH provides a wide working voltage up to 1.6 V and exhibits a maximum specific energy of 85 W h kg−1 at the specific power of 726 W kg−1 with a high capacity retention over 88% after 10 000 cycles, while the HES in 1 M KOH provides a lower maximum specific energy of 61 W h kg−1. A Fe(CN)63−/Fe(CN)64− redox couple has a great electrochemical reversibility in nature since Fe(CN)63− can obtain electrons from Ni(OH)2 through the reduction process and Fe(CN)64− can donate electrons to NiOOH for the oxidation process. The HES reported herein may be practically used for high energy applications.

Fracture behavior of silica nanoparticles reinforced rubber/epoxy composite:

Hybrid composites consisting of soft rubber (carboxyl-terminated butadiene acrylonitrile, CTBN) and silica nanoparticles with average particle size of 20 nm were studied for improving toughness of epoxy resins (diglycidyl ether of bisphenol A, DGEBA). The hybrid carboxyl-terminated butadiene acrylonitrile /silica nanoparticles epoxy systems exhibited improvements in the Young’s modulus, and more importantly, fracture toughness (KIC), which can be explained by synergistic impact from the inherent characteristics of each filler. In this study, the highest KIC was reached with addition of small amounts of silica nanoparticles (5 vol.%) to the epoxy containing 15 vol.% carboxyl-terminated butadiene acrylonitrile, where the KIC was distinctly higher than with the epoxy containing carboxyl-terminated butadiene acrylonitrile or silica nanoparticles alone. Cavitation of rubber particles with matrix dilation and particle debonding with subsequent void growth were determined as the toughening mechanisms responsible for the toughness improvements for epoxy. The evidence indicates that debonding of the silica nanoparticles causes a weakening of the matrix–particle interface. The toughness enhancement in hybrid nanocomposites involves an increase in silica nanoparticles particle debonding an increase in plastic zone size, which allows the epoxy matrix to dissipate more fracture energy.

Natural Rubber Reinforced with Silica Nanoparticles Extracted from Jasmine and Riceberry Rice Husk Ashes

Silica nanoparticles were synthesized by rice husk ash (RHA) produced from jasmine rice husk and riceberry rice husk via sol-gel method for the use as reinforcing fillers in natural rubber (NR). The obtained silica nanoparticles are spherical in shape and the particle sizes were observed to be in the 10-20 nm range with uniformly size distribution. The surface of silica nanoparticles was treated with a silane coupling agent confirmed by FTIR. The treated silica nanoparticles were then incorporated into NR and vulcanized with electron beam irradiation. The rubber nanocomposites with silica nanoparticles, produced from jasmine rice husk and riceberry rice husk, resulted in higher mechanical properties (tensile strength and modulus) than neat rubber vulcanizate. The modified rubber vulcanizates revealed rougher surface with tear lines as compared to the neat rubber vulcanizates, indicating the improved strength. Interestingly, the rubber nanocomposites with silica nanoparticles from jasmine rice husk showed higher tensile strength and modulus than silica nanoparticles produced from riceberry rice husk. The micrographs indicated better dispersion of NR composites with jasmine rice husk which leads to a strong interaction between silica nanoparticles and rubber matrix, thereby improving the strength.

Extraction of Nanocellulose from Dried Rubber Tree Leaves by Acid Hydrolysis

Nanocellulose were extracted from dried rubber tree leaves by acid hydrolysis. The dried rubber tree leaves were treated by the alkali and bleaching process to obtain the bleached cellulose powder. Acid hydrolysis from sulfuric acid (H2SO4) at different concentrations (35 wt.% to 65 wt.%) was performed to obtain the nanocellulose. The extracted nanocellulose were characterized by the transmission electron microscope (TEM), atomic force microscope (AFM), Fourier transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD). The produced nanocellulose exhibited rod-like shaped cellulose nanocrystals (CNCs), however, the CNCs structure and crystallinity depended on the H2SO4 concentration. It was revealed that the higher H2SO4 concentration led to the shorter CNCs lengths. In addition, the crystallinity was generally found to increase with increasing acid concentration treatments but slightly reduce at 65 wt.% of H2SO4.

Effect of Gamma Radiation on Properties of Cellulose Nanocrystal/Natural Rubber Nanocomposites

Cellulose nanocrystals (CNC) were extracted from corn cob and synthesized by alkaline treatment using 3 wt% sodium hydroxide (NaOH). Acid hydrolysis with 64 wt% sulfuric acid (H2SO4) at different reaction times (30, 45, 60 min) was performed to obtain CNC solutions. CNC was evaluated as a reinforcing agent in natural rubber (NR) at CNC loadings from 1-5 wt%. Gamma-ray radiation was used as vulcanization method and varied at 10 and 20 kGy. The tensile modulus and tensile strength of NR vulcanizates increased with addition of CNC and contents. In addition, radiation by gamma ray impacts the mechanical performance, where CNC/NR composites vulcanized with higher dose of radiation of 20 KGy were found to have the higher values in tensile strength, elongation at break, and modulus than with 10 KGy. Moreover, the tensile strength and elongation at break of the composites after aging were found to slightly increase due to post-curing during the aging process.

Mechanical Behavior of Polystyrene-Grafted Natural Rubber/Natural Rubber Blend: Effect of Polystyrene Grafting Percentage

Polystyrene-grafted natural rubber (PS-GNR) at various graft levels was evaluated to improve mechanical properties of natural rubber (NR). PS-GNR was synthesized by emulsion copolymerization at 60°C at different reaction times between 15 and 360 mins to control the grafting levels of PS in the PS-GNR co-polymer. The resultant PS-GNR co-polymers were then blended into NR latex. The vulcanized NR compounds were investigated for the effect of PS grafting percentage in PS-GNR/NR compounds on mechanical properties, including tensile, tear strength and hardness. A core-shell structure was revealed with PS encapsulating the NR core via transmission electron microscopy. The polystyrene grafting percentage was determined to be 12.7%, 17.1%, 22.1% and 23.6% for polymerization times of 15 min, 60min, 120min, and 360 min, respectively. Addition of PS-GNR into NR exhibited biphasic behavior, resulting in a decrease in the tensile strength and tear strength. With further increase in grafting percentage of PS, the tensile strength and tear strength continues to decrease. The rigid chain of PS grafted onto NR surface reduced the elasticity of NR chain resulting in lower tear strength and the tensile strength. Fracture surface revealed a decrease in ductility of material with increasing grafting percentage of PS. On the other hand, modulus and hardness of PS-GNR/NR compounds were found to increase with increasing grafting percentage of PS. The addition of PS-GNR to rubber compound had shown an impact on dynamic behavior. With further increase in grafting percentage of PS in PS-GNR, an enhancement of storage modulus of rubber compound was clearly observed.

Effect of Cellulose Functionalization on Thermal and Mechanical Properties of Epoxy Resin

In this study, diglycidyl ether of bisphenol A (DGEBA) cured cycloaliphatic polyamine was modified with functionalized celluloses for improved thermal and mechanical properties. Three different types of surface-modified cellulose, polyacrylamide-g-cellulose (PGC), aminopropoxysilane-g-cellulose (SGC), and carboxymethyl cellulose (CMC), were investigated and used as reinforcing agents in epoxy resins. The storage modulus of these modified epoxy systems was found to significantly increase with addition of cellulose fillers (up to 1 wt. % cellulose content). An improved fracture toughness (KIC) was also observed with increasing cellulose loading content with PGC and SGC. Among the surface-modified celluloses, epoxy modified with SGC was found to have the highest fracture toughness followed by PGC and CMC at 1.0 wt.% cellulose addition due to the chemical surface compatibility. The toughening mechanisms of the cellulose/epoxy composites, measured by scanning electron microscopy (SEM), revealed that fiber-debonding, fiber-bridging, and fiber-pull out were responsible for increased toughness.

Degradation of Silica-Reinforced Natural Rubber by UV Radiation and Humidity in Soil

In this research study, the degradation of natural rubber was applied for applications in agriculture products such as rubber mulch. This work included the synthesis of 20% wt silica/ natural rubber composites from high ammonia concentrate latex (HA) and fresh latex (FL). They were casted by film casting. The experimental study of rubber composite degradation was done by putting the samples underground and above the soil surface under accelerated degradation test box equipped with a solar simulator lamp for a period of 50 days. Samples were characterized by scanning electron microscopy (SEM) to examine the dispersion on cross-sectional area between natural rubber and silica. Thermogravimetric analysis (TGA) was used to analyze the thermal stability of the composites. Tensile strength (MPa), modulus at 100% elongation (MPa), and elongation at break (%) of the samples after aging were tested by focusing on. It was found that thermal degradation of natural rubber compounds consisted of one step of mass loss between 341°C and 455°C. The SEM result showed good dispersion of Si in the rubber samples. Moreover, it was found that before aging, the composite samples had higher tensile strength than that of the rubber. After aging, the composite samples had lower tensile strength than that of the rubber. Elongation @ break value of HA/Si and FL/Si after aging were decreased obviously.