Furthermore, the CS velocity test revealed fast kinetics and 82% power retention from 2C to 10C. Furthermore, the interfacial adhesion interactions between the glass fiber and the epoxy matrix were highly tunable by simply changing the composition and architecture of the layers, taking advantage of the versatility of the LbL assembly. Surface free energy of the multilayer coated glass fibers with different assembly and their corresponding schemes showing the glass fiber (sky blue), GO layer (grey) and ANF layer (orange). a) Schematic representation of the microbond test for interfacial shear strength (IFSS).
Introduction
Synthesis of CS
- Hard templating synthesis
- Soft templating synthesis
- Hydrothermal condensation synthesis
- Microemulsion polymerization synthesis
- Extension of the Stöber method
However, inappropriate preparation of solid templates and hazardous etchant for template removal, such as HF and NaOH, are drawbacks of the HT method. In general, the ST method is simple and widely applicable for the synthesis of various types of CS including meso- and h-CS, as well as more complex CS.21 Despite challenges such as low yield, weak structural stability of the templates, wide particle size distribution, various studies are ongoing to overcome the drawbacks.
Application
- N, F-doped CS for supercapacitor
- N-doped hierarchically porous CS for oxygen reduction reaction
- Ultrahigh-surface-area hollow carbon sphere for energy storage
Lu and co-workers achieved the application of the Stöber method to synthesize CS,34 realizing that the silica sphere sol-gel reaction is applicable to the resorcinol-formaldehyde reaction for the formation of polymeric spheres. The Stöber method, which has been dedicated to the synthesis of various CS structures, has offered real opportunities by combining with other synthetic strategies, such as The disadvantage of Stöber methods is the limited choice of precursors, but efforts to find suitable reagents for the Stöber method are ongoing in various ways.
The electrochemical performance of N-doped CS with 1280 m2/g specific surface area was compared with that of a platinum-based electrocatalyst. Wu and co-workers synthesized hollow CS with ultra-high surface area without hard templates such as silica spheres, using the triton X-100 micelle as a soft template.26 After carbonization of pyrrole and aniline comonomer along with the micelle, h- CS with 3,022 m2 was synthesized / g specific surface area. Nitrogen-doped ultra-high surface area h-CS was used for various applications, such as organic vapor adsorption, supercapacitor, and Li-S battery electrode materials.
The prepared CS of PDA-MA resin possesses a specific surface area of 575 m2/g, spherical shape with diameter about 1-2 µm, and significant content of nitrogen doping. Considering that further optimization of the size of CS and specific surface area is in progress, the CS made of PDA-MA resin is expected to offer utility value for energy storage applications.
Experimental method & materials
- Synthesis of phenylenediamine-mellitic acid (PDA-MA) resin
- Synthesis of carbon sphere (CS)
- Characterizations
- Cell fabrication and measurements for Li-ion battery
Müllen and co-workers prepared hierarchical micro-, mesoporous CS with nitrogen doping and tested them for ORR catalysts.5 Porous CS with micro-, mesopores were synthesized by using silica nanoparticles as a template and activating CS with ammonia. When Zn–air batteries were fabricated with CS as ORR catalysts, the CS catalysts showed better performance compared to the state-of-the-art Pt/C catalyst. Hollow carbon spheres are attractive porous carbon material with the unique characteristics of low density and large internal cavity.
The synthesis of PDA-MA resin involves the hydrothermal reaction of three isomers of PDA and MA (Tokyo Chemical Industry Co.) in water or ethanol as a solvent. Among the PDA-MA resin samples, the spherical resin, synthesized from m-PDA and MA in the hydrothermal reaction, was thermally treated for two hours for carbonization. Carbon coating of CS was performed by flowing acetylene gas (500 sccm) at the same temperature as the carbonization of PDA-MA resin for 10 min.
Nitrogen adsorption/desorption isotherms were analyzed at 77 K with ASAP2420 (Micromeritics Instruments), and specific surface area was calculated by the Brunauer–. The paste of the mixture is applied to Cu foil with a squeegee and dried at 150 °C vacuum.
Results & discussion
Synthesis of N-doped CS from PDA-MA resin
The coin cells were tested by galvanostatic charge/discharge at different scan rates between 3.0 V and 0.01 V (vs. Li/Li). Galvanostatic measurements were performed by WBCS-3000 battery cyclers (Wonatech Co.) at room temperature. a) o-PDA-MA, (c) m-PDA-MA and (e) p-PDA-MA resin synthesized by solvothermal ethanol reaction. The SEM image shows the morphology of the CS after the carbonization showing uniform spherical shape and diameter ranging from 1 to 2 µm.
The broad and rather characteristic peaks from the background peak indicate dominant amorphous carbon structures of typical hard carbon. Raman spectra of CS/700Ar and CS/700H2 show D band located at 1.363 cm-1 and G band located at 1.590 cm-1, attributed to the vibrational peak of defective carbon and the vibrational peak of sp2-bonded carbon, respectively ( Figure 5c). Chemical states of elements in Resin and CS were investigated by XPS (Figure 5d-5f), which revealed typical peaks for C1s, N1s and O1s in the XPS recording spectra.
High-resolution XPS spectra of C1s and N1s were further deconvoluted to analyze the bonding state of carbon and nitrogen. The appearance of a significant graphitic-N content, which is bonded to three carbon atoms in the graphene plane, indicates successful doping of nitrogen in the structure of CS.
Electrochemical performance of N-doped CS as an anode material
Degradation results from irreversible reaction with residual functional groups or terminal hydrogen of CS. The trend suggests that slow activation of CS with more reaction sites.37 The rate capability has been investigated to measure the discharge-charge rate-dependent capacitance. The superior performance of the CS/700H2/CC was also shown with a high C rating compared to others.
The gradual C rate shift is performed to overcome poor initial coulombic efficiency and slow activation of CS. To highlight the superior rate capability of CS as shown above, a higher discharge rate of 1 C was measured. Considering the condition of the higher C rate of the two samples, CS with the higher carbonization temperature showed improved cycling performance.
In contrast to CS/700H2 having lower capacity than CS/700Ar, the cyclic performance graph shows enhanced capacity of CS/900H2/CC than that of CS/900Ar/CC. However, the rate capability of CS/900Ar/CC and CS/900H2/CC was degraded by elevated carbonization temperature.
Conclusion
Highly Tunable Interfacial Adhesion of Glass Fiber by Hybrid
Synthesis of positively charged graphene oxide (GO)
Graphite oxide was synthesized using a modified Hummer method 57 , 67 and then exfoliated by ultrasound to form a brown dispersion of GO in water. The resulting GO was negatively charged due to the presence of chemical functional groups such as carboxylic acids and alcohol groups. Negatively charged GO was converted to positively charged GO by N-ethyl-N'-(3-dimethyl aminopropyl) carbodiimide methiodide (EDC) chemistry.
Specifically, positively charged GO was synthesized by mixing 1.88 g of EDC (Sigma Aldrich) and 10 mL of ethylenediamine (99%, Sigma Aldrich) in 100 mL of negatively charged GO suspension (0.5 mg/mL) and soaking for 12 h. stir. The resulting suspension was dialyzed (MWCO Spectra/Por) for 7 days to remove any residues and byproducts. Prior to LbL deposition, the pH of the positively charged GO suspension was adjusted to 3 with the addition of 1.0 M HCl.
Synthesis of aramid nanofiber (ANF)
Surface modification of glass fibers by LbL assembly
The substrate was first dipped in a positively charged GO solution (0.50 mg/ml) at pH 3 for 10 min. It was then rinsed in fresh deionized (DI) water for 1 min twice and then in DMSO for 2 min to remove loosely bound GO. Next, the substrate was dipped in a negatively charged ANF suspension in DMSO for 10 min, and washed with DMSO twice for 1 min each and DI water for 2 min, forming a monolayer film of (GO/ANF)1 provided.
In the case of (GO/PSS)1, the substrate was first immersed in a positively charged GO solution for 10 min, then in DI water for 1 min twice, and finally, in 0.01 M NaCl for 2 min. Then, the substrate was immersed in a solution of 1 wt% PSS (Poly(sodium 4-styrenesulfonate), Mw ~ 70,000, Sigma-Aldrich) in 0.10 M NaCl for 10 min, after which it was washed with fresh DI water for 1 min three. times each. For (PDAC/ANF)1, the substrate was first immersed in a solution of 1 wt% PDAC (poly(diallyl dimethylammonium chloride), Mw < 100,000, Sigma-Aldrich), then in DI water for 1 min twice and, bottom, in DMSO for 2 min.
Then, the substrate was immersed in ANF suspension for 10 min and washed twice with DMSO for 1 min and with DI water for 2 min. Before surface modification of the glass fibers by LbL assembly, the glass fibers were treated with O2 plasma for 30 seconds to obtain a negatively charged surface.
Sample preparation for microbond test
The glass substrate used in the model system was cleaned with piranha solution (7:3 H2SO4/H2O2) for 1 hour to remove any organic contamination. Then, all other films were coated on fiberglass in the same manner as for the model system.
Characterizations
The surface morphology of the multilayers deposited on glass fiber was examined by SEM as shown in Figure 4. Likewise, ANF10 was successfully deposited on the surface of glass fibers by LbL assembly. The enlarged image in Figure 4b shows the one-dimensional fibrillar microstructure of ANF in multilayers.
We also confirmed that the mounting condition did not damage the original morphology of the glass fiber during the surface modification process. Surface free energy of the multilayer coated glass fibers with different assembly and their corresponding schemes representing the glass fiber (sky blue), the GO layer (gray) and the ANF layer (orange). It is thus estimated that the ANF modification causes an increase in the dispersive part of the SFE, which is not the case for the polar part.
Thus, it is clear that the integration of GO and ANFs with the LbL assembly can simultaneously improve both the polar and dispersive parts of the SFE. The configuration of the GO and ANF layers had a significant impact on the surface properties of the glass fiber. In particular, the increase in the polar and dispersive parts of the SFE of the multilayer coated glass fibers is mainly attributed to the GO and ANF layers, respectively.
The improvement of the IFSS between the glass fiber and the epoxy matrix was consistent with the overall SFE of the multilayer coated glass fiber, which depends on the configuration of the GO and ANF multilayers.
