Boosting the Capacitive Performance of Supercapacitors by Hybridizing N, P-Codoped Carbon Polycrystalline with Mn3O4-Based Flexible Electrodes.

Chitosan, a biomass raw material, was utilized as a carbon skeleton source and served as a nitrogen (N) atom dopant in this study. By co-doping phosphorus (P) atoms from H3PO4 and nitrogen (N) atoms with a carbon (C) skeleton and hybridizing them with Mn3O4 on a carbon fiber cloth (CC), an Mn3O4@NPC/CC electrode was fabricated, which exhibited an excellent capacitive performance. The N, P-codoped carbon polycrystalline material was hybridized with Mn3O4 during the chitosan carbonization process. This carbon polycrystalline structure exhibited an enhanced conductivity and increased mesopore content, thereby optimizing the micropore/mesopore ratio in the electrode material. This optimization contributed to the improved storage, transmission, and diffusion of electrolyte ions within the Mn3O4@NPC electrode. The electrochemical behavior was evaluated via cyclic voltammetry and galvanostatic charge-discharge tests using a 1 M Na2SO4 electrolyte. The capacitance significantly increased to 256.8 F g-1 at 1 A g-1, and the capacitance retention rate reached 97.3% after 5000 charge/discharge cycles, owing to the higher concentration of the P-dopant in the Mn3O4@NPC/CC electrode. These findings highlight the tremendous potential of flexible supercapacitor electrodes in various applications.

The Efficiency Study of Graphene Synthesis on Copper Substrate via Chemical Vapor Deposition Method with Methanol Precursor.

Few-layer graphene was successfully synthesized on copper foil via chemical vapor deposition with methanol as a carbon source. This was confirmed by optical microscopy observation, Raman spectra measurement, I2D/IG ratio calculation, and 2D-FWHM value comparisons. Monolayer graphene was also found in similar standard procedures, but it required higher growth temperature and longer time periods. The cost-efficient growth conditions for few-layer graphene are thoroughly discussed via TEM observation and AFM measurement. In addition, it has been confirmed that the growth period can be shortened by increasing growth temperature. With the H2 gas flow rate fixed at 15 sccm, few-layer graphene was synthesized at the lower growth temperature of 700 °C in 30 min, and at 900 °C growth temperature in only 5 min. Successful growth was also achieved without adding hydrogen gas flow; this is probably because H2 can be induced from the decomposition of methanol. Through further defects study of few-layer graphene via TEM observation and AFM measurement, we tried to find possible ways for efficiency and quality management in graphene synthesis in industrial applications. Lastly, we investigated graphene formation after pre-treatment with different gas compositions, and found that gas selection is a crucial factor for a successful synthesis.

Hierarchical Porous Heteroatoms-Co-Doped Activated Carbon Synthesized from Coconut Shell and Its Application for Supercapacitors.

Coconut husk biomass waste was used as the carbon precursor to develop a simple and economical process for the preparation of hierarchical porous activated carbon, and the electrochemical properties of the electrode material were explored. The important process variables of carbonization, the weight ratios of the coconut shell/KOH, the amount of source dopant, and the carbonization temperature were investigated in order to reveal the influence of the as-obtained microporous/mesoporous/macroporous hierarchical porous carbon materials on the powder properties. Using a BET specific surface area analyzer, Raman analysis, XPS and SEM, surface morphology, pore distribution and specific surface area of the hierarchical porous carbon materials are discussed. The results show that the as-prepared N-, S- and O-heteroatom-co-doped activated carbon electrode was manufactured at 700 °C for electrochemical characteristics. The electrochemical behavior has the characteristics of pseudo-capacitance, and could reach 186 F g-1 at 1 A g-1 when measured by the galvanostatic charge-discharge (GCD) test. After 7000 cycles of the charge-discharge test, the initial capacitance value retention rate was 95.6%. It is predicted that capacitor materials made when using coconut shell as a carbon source will have better energy storage performance than traditional carbon supercapacitors.

Preparatory Conditions Optimization and Characterization of Hierarchical Porous Carbon from Seaweed as Carbon-Precursor Using a Box-Behnken Design for Application of Supercapacitor.

This study has developed an environmentally friendly, simple, and economical process by utilizing seaweed as a carbon precursor to prepare a hierarchical porous carbon for the application of a supercapacitor. In the carbonization process, the design of experiment (DOE) technology is used to obtain the optimal preparatory conditions with the best electrochemical properties for the electrode materials of supercapacitors. Without using strong acid and alkali solution of the green process, NaCl is used as the pore structure proppant of seaweed (SW) for carbonization to obtain hierarchical porous carbon material to improve the pore size distribution and surface area of the material. In the experiment of SW activation, the interaction between factors has been explored by the response surface methodology (RSM) and Box-Behnken design, and the optimal conditions are found. The activated carbon with the specific surface area of 603.7 m2 g-1 and its capacitance reaching 110.8 F g-1 is successfully prepared. At a current density of 1 A g-1, the material still retains 95.4% of the initial capacitance after 10,000 cycles of stability testing. The hierarchical porous carbon material prepared by the design of experiment planning this green process has better energy storage properties than supercapacitors made of traditional carbon materials.

Influence of the Addition of Dispersible Color Powder and Polyacrylic Emulsion on the Durability of Cement Mortar.

Cement mortar can be colored using color additive technology to give colorful facades to the surfaces of buildings, and to beautify the environment. In this study, weight ratios of color powder/cement at 1:80, 1:40, and 1:27, and polyacrylic emulsion/cement at a ratio of 1:5 were added as pigments to cement mortar; the fresh properties, slump, slump flow, hardened properties, compressive strength, flexural strength, ultrasonic pulse velocity, durability, surface electrical resistivity and thermal conductivity of the colored cement mortar were then examined. The results showed that adding color powder/cement at 1:80 and polyacrylic emulsion/cement at 1:5 gives the best water/cement (W/C) ratio, which equals 0.5; this can effectively improve the hardness and durability of colored cement mortar. At 28 days of aging, the strength of the various colored cement mortars was maintained at 33.1-36.8 MPa. The acrylic-based emulsion significantly improved the flexural strength of the specimen. At 91 days of aging, all of the cement mortars exceeded the control group, with an anti-bay strength of 19.9-21.7 MPa, and the strength increased with aging. Adding appropriate amounts of inorganic color powder and mixing water can effectively enhance the fresh and hardened properties and durability of the colored cement mortar, while polyacrylic emulsion may significantly improve the test pieces and flexural strength, which increases with age. Moreover, natural α-Fe2O3 (rust layer) is formed on the surface of the colored cement mortar samples through the addition of inorganic color powder that contains Fe(III) ion; this prevents the intrusion of noxious ions and thus increases the durability. All of the test pieces of colored cement mortar in this study had a surface resistance of over 20 kΩ-cm on the seventh day of the test period, meaning good surface compactness. In addition, because the thermal conductivity of the added inorganic color powder was higher than that of cement, the thermal conductivity was significantly improved.

Facile Fabrication of MnO2/Graphene/Ni Foam Composites for High-Performance Supercapacitors.

A novel MnO2/graphene/Ni foam electrode was fabricated via the impregnation and electrochemical deposition technique with Ni foams serving as substrates and graphene serving as a buffer layer for the enhanced conductivity of MnO2. The samples were characterized using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Compared with other methods, our strategy avoids using surfactants and high-temperature treatments. The electrodes exhibited excellent electrochemical performance, high capabilities, and a long cycle life. Various electrochemical properties were systematically studied using cyclic voltammetry and electrochemical impedance spectroscopy. The results showed that the specific capacitance of the MnO2/graphene/Ni composite prepared at 1 mA cm-2 of electrodeposition could achieve a scan rate of 10 mV s-1 at 292.8 F g-1, which confirmed that the graphene layer could remarkably improve electron transfer at the electrolyte-electrode interface. The capacitance retention was about 90% after 5000 cycles. Additionally, a MnO2/graphene//graphene asymmetric supercapacitor was assembled and it exhibited a high-energy density of 91 Wh kg-1 as well as had an excellent power density of 400 W kg-1 at 1 A g-1. It is speculated that the strong adhesion between the graphene and MnO2 can provide a compact structure to enhance the mechanical stability, which can be applied as a new method for energy storage devices.

Influence of Fluorine-Containing Monomer Content on the Hydrophobic and Transparent Properties of Nanohybrid Silica Polyacrylate Coating Materials.

Nanosilica-modified, fluorine-containing polyacrylate hybrid coating materials, consisting of dodecafluoroheptyl methacrylate (DFMA), methyl methacrylate (MMA), 2-ethyl hexyl acrylate (2-EHA), 3-(trimethoxysilyl) propyl methacrylate (KH-570), and tetraethylorthosilicate (TEOS), are synthesized successfully by free radical polymerization and the sol-gel process. It is revealed that the content of the fluorine-containing polyacrylate hybrid coating materials from DFMA monomers significantly improves the properties of the films. The polyacrylate coating film prepared with a weight ratio of DFMA/MMA at 1:5 exhibits the largest water contact angle of 105.4°, which demonstrates that DFMA can effectively improve the hydrophobicity of the coating film. Moreover, the silicon coupling agent (KH-570) is used to graft silica with acrylate. Spherical in shape, the surface morphology of the nanohybrid film exhibits a core-shell structure, which increases the surface roughness and enhances the hydrophobic properties. The as-prepared fluorine-containing nanohybrid silica polyacrylate film possesses a high transmittance of 89-97% in the visible light region, indicating its potential as a very attractive solution in many practical areas.

Enhanced Activity of Hierarchical Nanostructural Birnessite-MnO2-Based Materials Deposited onto Nickel Foam for Efficient Supercapacitor Electrodes.

Hierarchical porous birnessite-MnO2-based nanostructure composite materials were prepared on a nickel foam substrate by a successive ionic layer adsorption and reaction method (SILAR). Following composition with reduced graphene oxide (rGO) and multiwall carbon nanotubes (MWCNTs), the as-obtained MnO2, MnO2/rGO and MnO2/rGO-MWCNT materials exhibited pore size distributions of 2-8 nm, 5-15 nm and 2-75 nm, respectively. For the MnO2/rGO-MWCNT material in particular, the addition of MWCNT and rGO enhanced the superb distribution of micropores, mesopores and macropores and greatly improved the electrochemical performance. The as-obtained MnO2/rGO-MWCNT/NF electrode showed a specific capacitance that reached as high as 416 F·g-1 at 1 A·g-1 in 1 M Na2SO4 aqueous electrolyte and also an excellent rate capability and high cycling stability, with a capacitance retention of 85.6% after 10,000 cycles. Electrochemical impedance spectroscopy (EIS) analyses showed a low resistance charge transfer resistance for the as-prepared MnO2/rGO-MWCNT/NF nanostructures. Therefore, MnO2/rGO-MWCNT/NF composites were successfully synthesized and displayed enhanced electrochemical performance as potential electrode materials for supercapacitors.

Recycling dredged harbor sediment to construction materials by sintering with steel slag and waste glass: Characteristics, alkali-silica reactivity and metals stability.

This work recovered the dredged sediment around Kaohsiung Harbor, Taiwan, for preparing lightweight aggregates (LWA), of which physicochemical properties as affected by the addition of basic-oxygen-furnace (BOF) slag and waste glass were investigated. LWA properties included water absorption, particle density, compressive strength, shrinkage, and microstructure of sintered pellets were evaluated to ensure feasibility of dredged harbor sediment reutilization technique. Results showed that adding appropriate amount of glass powders (~7%) to the mixtures of sediment and slag significantly reduced the water absorption (as low as 2.2%) of the sintered pellets and increase the compressive strength (as high as 23.1 MPa) of LWA, which were found to be controlled by open porosity and shrinkage. Excessive addition of glass (>10%) led to increase in internal pore sizes of the sintered pellets, and thus reduced the compressive strength. The alkali-silica reactivity (ASR) of the LWA was innocuous according to the ASTM C289 test. Sintering and glass addition improved the stability of heavy metal and environmental compatibility of the LWA. The recycling of waste sediment, slag, and glass for LWA production can provide an alternative for the disposal of dredge harbor sediment and has positive impact on waste reduction, which not only can reduce secondary contamination to the environment, but also can contribute to circular economy.

An Effective Electrodeposition Mode for Porous MnO2/Ni Foam Composite for Asymmetric Supercapacitors.

Three kinds of MnO2/Ni foam composite electrode with hierarchical meso-macroporous structures were prepared using potentiodynamic (PD), potentiostatic (PS), and a combination of PS and PD(PS + PD) modes of electrodeposition. The electrodeposition mode markedly influenced the surface morphological, textural, and supercapacitive properties of the MnO2/Ni electrodes. The supercapacitive performance of the MnO2/Ni electrode obtained via PS + PD(PS + PD(MnO2/Ni)) was found to be superior to those of MnO2/Ni electrodes obtained via PD and PS, respectively. Moreover, an asymmetric supercapacitor device, activated carbon (AC)/PS + PD(MnO2/Ni), utilizing PS + PD(MnO2/Ni) as a positive electrode and AC as a negative electrode, was fabricated. The device exhibited an energy density of 7.7 Wh·kg-1 at a power density of 600 W·kg-1 and superior cycling stability, retaining 98% of its initial capacity after 10,000 cycles. The good supercapacitive performance and excellent stability of the AC/PS + PD(MnO2/Ni) device can be ascribed to its high surface area, hierarchical structure, and interconnected three-dimensional reticular configuration of the nickel metal support, which facilitates electrolyte ion intercalation and deintercalation at the electrode/electrolyte interface and mitigates volume change during repeated charge/discharge cycling. These results demonstrate the great potential of the combination of PS and PD modes for MnO2 electrodeposition for the development of high-performance electrodes for supercapacitors.

Synthesis and characterizations of nanometric-sized TiO2 powders as a photocatalyst for water splitting.

Nanometric-sized titanium oxide (TiO2) powders were synthesized through two emulsions method. In which two solutions of reverse emulsion, one containing Ti4+ chelated with citric acid/cellulose aqueous droplets and the other aqueous ammonia droplets, with the same water/oil (w/o) ratio are mixed together to form a slurry of titanium citrate precursor. Then the precursors were recovered and calcined to form TiO2 at various temperatures. The powders prepared from volume ratio of w/o at 1/100 had a relatively uniform and spherical with less aggregation. When the volume ratio of w/o was increased, the particle size had more aggregation and bigger. The particle sizes of powders obtained from volume ratio of 1/100 were estimated to be 6-8 nm. Finally, photocatalytic experiments for water splitting and producing hydrogen was examined in methanol solution by utilizing 65 mg nanometric-sized Pt (0.6 wt%)/TiO2 powder, and about 70 micromol hydrogen was produced in 6 h.