Degeneration of Key Structural Components Resulting in Ageing of Supercapacitors and the Related Chemical Ageing Mechanism.

The research on supercapacitors (SCs) is one of the hot topics in the field of energy storage, and the intrinsic ageing mechanism of SCs is significant from both the economic and the scientific point of view. In this paper, the negative effects of decay of the key structural components on ageing of SCs were investigated by factorial design and analysis of variance (ANOVA). The ANOVA results showed that the degree of the negative influence on ageing of SCs could be ranked in descending order as anode > separator > cathode. The ageing would be accelerated due to the interaction between the electrode and separator, especially at a high charge-discharge current density. Further, the intrinsic chemical ageing mechanism of SCs was revealed by the morphology, microstructure, and chemical composition analyses of the fresh and aged key components (the electrode carbon materials, current collectors, and separators) with scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectra (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), etc. Moreover, the minimum pore width of electrode carbon materials suitable for electrolyte ion diffusion was obtained by density functional theory (DFT) calculations, which corroborated the assumption that the pore structure deterioration was one of the direct causes of capacitance loss for aged SCs. Generally, the ageing mechanism of key components of SCs could be a reference to develop advanced electrode materials and separators for SCs.

Preparation of Lotus Root-Type Monolithic-Activated Carbons with an Hierarchical Pore Structure from Rice Husks and Their Adsorption of Vitamin B12.

Activated carbon is widely used in many fields because of its well-developed pore structure. Especially in hemoperfusion, activated carbon beads derived from macroporous resin spheres are the predominant adsorbents in hemoditoxifiers. In comparison, biomass-activated carbon attracts more extensive attention on account of its renewability and environmental protection. In this study, a lotus root-type monolithic-activated carbon with a hierarchical pore structure was made from rice husks by the injection molding process followed by carbonization and activation. The straight square channels with the side length of about 1.3 mm were designable, and these channels with adjustable lengths were favorable for the fluid flow during blood purification compared with the tightly packed carbon beads in commercialized hemoditoxifiers. Complementally, the hierarchical nano-sized pores in the walls of the big channels would contribute much to the adsorption capacity for the monolith. Specifically, the adsorption of vitamin B12, a representative of middle molecular toxins in human blood, was about 3.7 mg g-1, which was acquired by simulated in vitro hemoperfusion tests and this demonstrated the promising application of the lotus root-type biomass-activated carbon in hemoperfusion.

Experimental and Theoretical Investigation of Laser Pretreatment on Strengthening the Heterojunction between Carbon Fiber-Reinforced Plastic and Aluminum Alloy.

Besides aluminum alloys, lightweight carbon fiber-reinforced plastics (CFRPs) have been adopted progressively in automobiles to save energy and reduce emission, so constructing a reliable heterojunction between aluminum alloys and CFRPs has come to be the key issue. In this study, ultrafast picosecond infrared (IR) and excimer ultraviolet (UV) lasers were introduced to pretreat the joint surface to enhance the adhesive strength. Scanning electron microscopy, white light interferometry, and X-ray photoelectron spectroscopy examinations indicated that because the energy absorptivities for the two lasers were different, the variation of the roughness, wettability, and chemical composition were a little different for the patterned surface. Correspondingly, the shear strengths of the adhesive joints were increased from 5.6 to 24.8 and 21.9 MPa for IR and UV laser-pretreated samples, respectively. Furthermore, finite element analysis was adopted to evaluate the effects of strengthened mechanical interlocking and fortified chemical bonding force on the enhancement of joint strength. It was shown that chemical bonding, instead of mechanical interlocking, played the dominant role in reinforcing the heterogeneous joints. As a whole, the picosecond IR laser was more preferable for surface pretreatment in adhesive heterojunctions due to its higher processing and enhancing efficiency.

Hierarchically Mesostructured Aluminum Current Collector for Enhancing the Performance of Supercapacitors.

Aluminum (Al) current collector is one of the most important components of supercapacitors, and its performance has vital effects on the electrochemical performance and cyclic stability of supercapacitors. In the present work, a scalable and low-cost, yet highly efficient, picosecond laser processing method of Al current collectors was developed to improve the overall performance of supercapacitors. The laser treatment resulted in hierarchical micro-nanostructures on the surface of the commercial Al foil and reduced the surface oxygen content of the foil. The electrochemical performance of the Al foil with the micro-nanosurface structures was examined in the symmetrical activated carbon-based coin supercapacitors with an organic electrolyte. The results suggest that the laser-treated Al foil (laser-Al) increased the capacitance density of supercapacitors up to 110.1 F g-1 and promoted the rate capability due to its low contact resistance with the carbonaceous electrode and high electrical conductivity derived from its larger specific surface areas and deoxidized surface. In addition, the capacitor with the laser-Al current collector exhibited high cyclic stability with 91.5% capacitance retention after 10 000 cycles, 21.3% higher than that with pristine-Al current collector due to its stronger bonding with the carbonaceous electrode that prevented any delamination during aging. Our work has provided a new strategy for improving the electrochemical performance of supercapacitors.

A gelatin composite scaffold strengthened by drug-loaded halloysite nanotubes.

Mechanical properties and anti-infection are two of the most concerned issues for artificial bone grafting materials. Bone regeneration porous scaffolds with sustained drug release were developed by freeze-drying the mixture of nanosized drug-loaded halloysite nanotubes (HNTs) and gelatin. The scaffolds showed porous structure and excellent biocompatibility. The mechanical properties of the obtained composite scaffolds were enhanced significantly by HNTs to >300%, comparing to those of gelatin scaffold, and match to those of natural cancellous bones. The ibuprofen-loaded HNTs incorporated in the scaffolds allowed extended drug release over 100h, comparing to 8h when directly mixed the drug into the gelatin scaffold. The biological properties of the composite scaffolds were investigated by culturing MG63 cells on them. The HNTs/gelatin scaffolds with excellent mechanical properties and sustained drug release could be a promising artificial bone grating material.

Fabrication and molecular dynamics analyses of highly thermal conductive reduced graphene oxide films at ultra-high temperatures.

Thin films with high thermal conductivity are urgently needed as heat dissipation materials for electronic devices. In this study, we developed a readily scalable roller coating method followed by ultra-high temperature annealing to prepare large-sized, free-standing, and flexible reduced graphene oxide (rGO) films with high thermal conductivity. The in-plane thermal conductivity measured by a laser flash method for the sample annealed at 2800 °C was 826.0 W m-1 K-1, which was much higher than that of copper foil. X-ray diffraction, Raman, and SEM analyses indicated that, different from common chemical reduction, heat treatment at high temperature could not only remove O, H, and other impure elements but also develop the in-plane crystal size of graphene and decrease the interlayer spacing of graphene sheets. Meanwhile, tight embedding during annealing and concomitant mechanical impaction was indispensable for retaining the shape and raising the density of the films. Furthermore, molecular dynamics analyses demonstrated that point defects, pentagonal/heptagonal defects, or even large in-plane holes in graphene could be rehabilitated to a great extent during ultra-high temperature annealing. In addition, real-time temperature monitoring demonstrated that the rGO films could act as an excellent thermal dissipation material in LED packages by reducing 10%-15% of the temperature increase.

Boosting supercapacitor performance of carbon fibres using electrochemically reduced graphene oxide additives.

Modifying conventional materials with new recipes represents a straightforward yet efficient way to realize large-scale applications of new materials. Electrochemically reduced graphene oxide (ERGO) coated carbon fibres (CFs), prepared as fibre-like supercapacitor electrodes, exhibited excellent electrochemical energy storage performance. Upon addition of only a small amount (~1 wt%) of ERGO, the hybrid fibres showed superior electrochemical capacitances (nearly three orders of magnitude enhanced) compared to pure CFs in both aqueous and gel electrolytes. Meanwhile, the energy density did not decrease notably as the power density increased. The superior capacitive performance could be attributed to the synergistic effect between wrinkled and porous ERGO sheets and highly conductive CFs. This fibre electrode material also offered advantages such as easy operation, mass production capability, mechanical flexibility and robustness, and could have an impact on a wide variety of potential applications in energy and electronic fields.

Preparation of sulfonated porous carbon nanotubes/activated carbon composite beads and their adsorption of low density lipoprotein.

The high level of low density lipoprotein (LDL) in plasma is the main cause of atherosclerosis. Hemoperfusion is an ideal therapy to lower the level of LDL in human blood system while therapeutic effect is determined by the adsorbent. The adsorbent must have suitable pore structure and specific functional groups. Carbon nanotubes (CNTs) could be a new adsorbent material because CNTs have high specific surface area and they can be modified by a variety of functional groups. Porous carbon composite beads with the CNTs and phenolic resin mixture were synthesized by suspension polymerization, following with carbonization and steam-activation. Then the porous composite beads were sulfonated with a sulfanilic acid anhydrous by diazotization and coupling reaction. The potential application of the sulfonated porous composite beads in adsorbing low density lipoprotein (LDL) from human serum was investigated. The results showed that the sulfonic acid groups on the composite beads could lower LDL levels greatly by electrostatic interaction with electropositive LDL. The higher 20-100 nm pore volume the composite beads had, the more LDL they could adsorb. The 20-100 nm pore volume was enhanced by adding more CNTs and improving CNTs dispersion (ultrasonic crushing). The sulfonated composite beads containing 45 wt% CNTs presented the highest adsorption capacity to LDL 10.46 mg/g, showing a good prospect as LDL adsorbent in hemoperfusion.

Multifunctional graphene/platinum/Nafion hybrids via ice templating.

We report the synthesis of multifunctional hybrids in both films and bulk form, combining electrical and ionic conductivity with porosity and catalytic activity. The hybrids are synthesized by a two-step process: (a) ice templation of an aqueous suspension comprised of Nafion, graphite oxide, and chloroplatinic acid to form a microcellular porous network and (b) mild reduction in hydrazine or monosodium citrate which leads to graphene-supported Pt nanoparticles on a Nafion scaffold.

Sonophotocatalytic degradation of methyl orange by carbon nanotube/TiO2 in aqueous solutions.

In this study, carbon nanotubes (CNTs)/TiO2 composite were prepared and the sonophotocatalytic activity of CNTs/TiO2 nanoparticles was investigated, in which methyl orange (MO) was chosen as an object. The results indicate that the photocatalytic efficiency of CNTs/TiO2 remarkable increases in the presence of ultrasound, and the sonophotocatalysis process followed a first-order kinetics. The kinetic constant of CNTs/TiO2 for the MO degradation is 2.2 times higher than that of P25, which indicated that the sonophotocatalytic ability of CNTs/TiO2 is obviously higher than P25 powder.

[Electricity generation by the microbial fuel cells using carbon nanotube as the anode].

The characteristic of anode plays an important role in the performance of the microbial fuel cell (MFC). Thus, carbon nanotube (CN), flexible graphite (FG) and activated carbon (AC) were used as anode material in this study, and the performances of three MFCs (CN-MFC, FG-MFC and AC-MFC) were studied. The results show that CN is a kind of suitable material to be used as anode in the MFC. The maximal power densities of CN-MFC, FG-MFC and AC-MFC are 402,354 and 274 mW/m2, respectively. The CN-MFC shows a higher power density and coulombic efficiency compared with FG-MFC and AC-MFC. The CN-anode can reduce the internal resistance obviously. The internal resistances of CN-MFC, AC-MFC and FG-MFC are 263, 301 and 381 omega, respectively. The protein contents on the CN-anode, AC-anode and FG-anode are 149, 132 and 92 microg/cm2 after stable operation, and there is a positive relation between the protein content and internal resistance. The conductivity of the three types of MFCs from high to low was FG-MFC, CN-MFC and AC-MFC, which was accordant with the ohmic resistance. The stable times of CN-MFC, FG-MFC and AC-MFC, which were needed to measure the internal resistances, were 1800, 1200 and 300 s respectively.