RESUMEN
We present a novel approach for the synthesis of large-pore mesoporous carbon with a highly porous structure, based on an oil/water (O/W) emulsion templating method. For the formation of oil-in-water emulsions with nanoscale oil droplets, polyvinylpyrrolidone was used as an emulsifier. Mesoporous carbon materials with large mesopores were successfully synthesized via a three-step process: (1) polymerization in the oil-in-water emulsion, (2) filtration, and (3) carbonization. We confirmed that the pore size of the carbon can be significantly reduced through a modified O/W emulsion method. The mesoporous carbon materials prepared without an activation step exhibited an appreciable surface area (705 m2/g) and a noticeable capacitive performance of â¼100 F/g at 2.0 A/g. We believe that the approach presented here can be widely applied to the synthesis of mesoporous carbon using various carbon sources, and the structural properties of the mesoporous carbon can be improved through proper optimization.
RESUMEN
To obtain a high S-loading cathode for a Li-S battery, we propose a free-standing carbon nanotube (CNT)-based S cathode, which consists of two layers: a pure S deposition layer with a thickness of 20 µm, and a S-containing CNT film (S-CNT). Based on scanning electron microscopic (SEM) studies, it was observed that the S layer completely vanished when the cell with the S/S-CNT cathode was discharged to 2.1 V after cell assembly, indicating that the thick sulfur film dissolved in the form of polysulfide intermediates during discharge. The proposed S/S-CNT cathode delivered double the areal capacity with good capacity retention of 83% after 100 cycles, compared with that of the control cathode (S-CNT). Thus, we believe that our new cathode design will be useful in developing stable, high-energy Li-S batteries.
RESUMEN
An ingenious design for a three-layer sulfur cathode is demonstrated, in which the pure sulfur layer is sandwiched between carbon nanotube (CNT) films. The unique feature of this particular model is that the sulfur layer does not contain any conductive materials, and therefore, the top CNT film of the prepared three-layer CNT/S/CNT electrode is electrically isolated from the bottom CNT film. Scanning electron microscopy studies revealed that the three-layer cathode was transformed into a single CNT cathode, with proximate contact between the two CNT films in the upper plateau of the first discharge. The lithium-sulfur cells employing a CNT/S/CNT cathode exhibited remarkably enhanced performance in terms of the specific capacity, rate property, and cycling stability compared to the cells with a sulfur-coated CNT cathode. This can mainly be attributed to the top CNT film, which serves not only as an interlayer to trap the migrating polysulfides, but also as an electrode to facilitate the redox reaction of active materials. Such an innovative approach is promising as it may promote the rational design of high-performance sulfur cathodes.
RESUMEN
This study presents a new approach for enabling the development of high-performance lithium-sulfur (Li-S) cells by simply inserting a sulfur-infused separator (SIS) between a common S cathode and a Li metal anode. All solid sulfur electrically isolated from the cathode is electrochemically reduced to polysulfides during the first discharge. Notably, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) studies have demonstrated that the S in the separator disappears completely even when the cell is discharged to 2.1 V in the first cycle. The combination of a SIS with a typical S cathode results in the doubling of the areal capacity with superior cycling stability upon comparison with the control cell. This result demonstrates that the introduction of additional active materials, such as elemental sulfur, to a separator is a highly effective method for the fabrication of Li-S cells with a high areal capacity.
RESUMEN
The use of carbon nanotube (CNT) films as a sulfur host is a promising approach to improve the sulfur loading and energy density of Li-S batteries. However, the inability to durably incorporate polysulfides within the cathode structure results in a limited cycle life. Herein, we propose a CNTbased sulfur cathode with carbon-coated ordered mesoporous silica (c-OMS) to overcome the cycle performance issue. Scanning electron microscopy and X-ray diffraction studies on the c-OMS prepared in this work revealed that the wall surface of OMS was evenly coated with an extremely thin carbon layer. The sulfur-CNT cathode with c-OMS retained a remarkably improved capacity (942 mAh g-1) with excellent cycling stability (91%) after 100 cycles as well as significantly high sulfur utilization in the first cycle compared with the sulfur-CNT cathode with OMS. This result may stem from the surface property of c-OMS with high chemical affinity towards electrolyte solvents.
RESUMEN
The removal of heavy-metal ions from wastewater is an important objective from a public-health perspective, and chelating agents can be used to achieve this aim. Herein, we report the synthesis of mesoporous carbon as a chelating polymer host using nanoarchitectonics approach. Carboxymethylated polyethyleneimine, a chelating polymer, was incorporated into the mesopore walls of mesoporous carbon to create a polymer-mesoporous-carbon composite. Nitrogen adsorption- desorption experiments and scanning electron microscopy (SEM) were used to illustrate the structural advantages of the composite. Co2+ adsorption by the composite material was examined using cobalt nitrate solutions at pH 3. The study revealed that the Co2+-absorption data are most closely modeled by the Langmuir isotherm. The maximum adsorption capacity, calculated by linear regression, was determined to be about 40 mg-Co/g-composite at pH 3. The composite exhibited about a six-times higher adsorption capacity toward a dilute Co solution (12.5 ppm) than that of the pristine mesoporous carbon. In addition, the composite showed a substantially higher distribution coefficient (Kd = 1.54×105) compared to that (Kd = 2.05×10²) of the mesoporous carbon. Overall, we expect that the mesoporous composite, with its large mesopores (~20 nm), will be in high demand for adsorption applications.