163 research outputs found
High-performance supercapacitors based on hierarchically porous carbons with a three-dimensional conductive network structure
Clews of polymer nanobelts (CsPNBs) have the advantages of inexpensive raw materials, simple synthesis and large output. Novel clews of carbon nanobelts (CsCNBs) have been successfully prepared by carbonizing CsPNBs and by KOH activation subsequently. From the optimized process, CsCNBs*4, with a specific surface area of 2291 m2 gâ1 and a pore volume of up to 1.29 cm3 gâ1, has been obtained. Fundamentally, the CsCNBs possess a three-dimensional conductive network structure, a hierarchically porous framework, and excellent hydrophilicity, which enable fast ion diffusion through channels and a large enough ion adsorption/desorption surface to improve electrochemical performance of supercapacitors. The product exhibits a high specific capacitance of 327.5 F gâ1 at a current density of 0.5 A gâ1 in a three-electrode system. The results also reveal a high-rate capacitance (72.2% capacitance retention at 500 mV sâ1) and stable cycling lifetime (95% of initial capacitance after 15â000 cycles). Moreover, CsCNBs*4 provides a high energy density of 29.8 W h kgâ1 at a power density of 345.4 W kgâ1 in 1 M tetraethylammonium tetrafluoroborate/acetonitrile (TEABF4/AN) electrolyte. These inspiring results imply that this carbon material with a three-dimensional conductive network structure possesses excellent potential for energy storage
Optimized synthesis of ultrahigh-surface-area and oxygen-doped carbon nanobelts for high cycle-stability lithium-sulfur batteries
Hierarchical clews of carbon nanobelts (CsCNBs) with ultrahigh specific surface area (2300 m2 gâ1) and large pore volume (up to 1.29 cm3 gâ1) has been successfully fabricated through carbonization and KOH activation of phenolic resin based nanobelts. The product possesses hierarchically porous structure, three-dimensional conductive network framework, and polar oxygen-rich groups, which are very befitting to load sulfur leading to excellent cycling stability of lithium-sulfur batteries. The composites of CsCNBs/sulfur exhibit an ultrahigh initial discharge capacity of 1245 mA h gâ1 and ultralow capacity decay rate as low as 0.162% per cycle after 200 cycles at 0.1 C. Even at high current rate of 4 C, the cells still display a high initial discharge capacity (621 mA h gâ1) and ultralow capacity decay rate (only 0.039% per cycle) after 1000 cycles. These encouraging results indicate that polar oxygen-containing functional groups are important for improving the electrochemical performance of carbons. The oxygen-doped carbon nanobelts have excellent energy storage potential in the field of energy storage
Konstrukcija mutanta bakterije Zymomonas mobilis pomoÄu mjesno-specifiÄne FLP rekombinaze
Flippase expression was carried out in Zymomonas mobilis strain ZM4. The FRT-flanked selection marker gene was first integrated into the ZM4 chromosome by homologous recombination. The Saccharomyces cerevisiae flp gene was then introduced under the control of the ZM4 gap gene promoter (Pgap, encoding glyceraldehyde-3-phosphate dehydrogenase) or the λ bacteriophage cI857-pR contained in the broad-host-range cloning vector pBBR1-MCS-2. This study demonstrated that flp was expressed and that the deletion frequency of the FRT-flanked marker gene was very high (approx. 100 %). In addition, the flp gene expression vector could be conveniently removed from the resulting unmarked Z. mobilis mutants by serially transferring the cells three times into antibiotic-free medium, thereby establishing an efficient method for constructing unmarked Z. mobilis mutants.U ovom je radu u soju bakterije bakterije Zymomonas mobilis ZM4 eksprimirana flipaza iz kvasca Saccharomyces cerevisiae. Najprije je homolognom rekombinacijom u bakterijski kromosom ugraÄen selektivni biljeg omeÄen FRT sekvencijama. Potom je u bakteriju unesen plazmid pBBR1MCS-2 koji sadrĆŸi kvaĆĄÄev gen Flp pod regulacijom promotora gena gap iz soja ZM4 (Pgap, koji kodira za gliceraldehid-3-fosfat dehidrogenazu) ili cI857-PR iz bakteriofaga λ. Gen Flp uspjeĆĄno je eksprimiran, te je uÄestalost gubitka selektivnog markera omeÄenog FRT sekvencijama iznosila pribliĆŸno 100 %. Osim toga, vektor za ekspresiju gena Flp lako je uklonjen trostrukim precjepljivanjem na podlogu bez antibiotika, pa se moĆŸe zakljuÄiti da je razvijena uÄinkovita metoda za uklanjanje selektivnog biljega iz transformanata bakterije Zymomonas mobilis
Facile synthesis of TiN nanocrystals/graphene hybrid to chemically suppress the shuttle effect for lithium-sulfur batteries
Herein, we present a microwave reduction strategy for the synthesis of reduced-graphene-oxide (rGO) supported TiN nanoparticle hybrid (TiN/rGO) under N2 atmosphere. The method involves GO reduction, metal oxide reduction and nitridation reaction in one single step. Due to TiN high conductivity and good interfacial affinity between it and lithium polysulfides (LiPSs), the prepared TiN/rGO-Sulfur (TiN/rGO-S) cathodes demonstrate rapid charge transfer, lower polarization, faster surface redox reaction kinetic and enhanced stability cycling performance than rGO-Sulfur (rGO-S) and TiO2/rGO-Sulfur (TiO2/rGO-S) cathodes. The initial capacity reaches 1197.6 mA h gâ1 with a reversible capacity of 888.7 mA h gâ1 being retained after 150 cycles at 0.1 C
Ultrahigh-content nitrogen-decorated nanoporous carbon derived from metal organic frameworks and its application in supercapacitors
Single electric double-layer capacitors cannot meet the growing demand for energy due to their insufficient energy density. Generally speaking, the supercapacitors introduced with pseudo-capacitance by doping heteroatoms (N, O) in porous carbon materials can obtain much higher capacitance than electric double-layer capacitors. In view of above merits, in this study, nanoporous carbon materials with ultrahigh N enrichment (14.23âŻwt%) and high specific surface area (942âŻm2âŻgâ1)âŻby in situ introduction of N-doped MOF (ZTIF-1, Organic ligands 5-methyltetrazole/C2H4N4) were produced. It was found that as supercapacitors' electrode materials, these nanoporous carbons exhibit a capacitance as high as 272âŻFâŻg-1âŻat 0.1âŻAâŻgâ1, and an excellent cycle life (almost no attenuation after 10,000 cycles.). Moreover, the symmetric supercapacitors were assembled to further investigate the actual capacitive performance, and the capacitance shows up to 154âŻFâŻg-1âŻat 0.1âŻAâŻgâ1. Such excellent properties may be attributed to a combination of a high specific surface area, ultrahigh nitrogen content and hierarchically porous structure. The results shown in this study fully demonstrate that the nanoporous carbon materials containing ultrahigh nitrogen content can be used as a potential electrode material in supercapacitors
Facile synthesis of ultrahigh-surface-area hollow carbon nanospheres and their application in lithium-sulfur batteries
Hollow carbon nanospheres (HCNs) with specific surface areas up to 2949â
m2âgâ1 and pore volume up to 2.9â
cm3âgâ1 were successfully synthesized from polyanilineâcoâpolypyrrole hollow nanospheres by carbonization and CO2 activation. The cavity diameter and wall thickness of HCNs can be easily controlled by activation time. Owing to their large inner cavity and enclosed structure, HCNs are desirable carriers for encapsulating sulfur. To better understand the effects of pore characteristics and sulfur contents on the performances of lithiumâsulfur batteries, three composites of HCNs and sulfur are prepared and studied in detail. The composites of HCNs with moderate specific surface areas and suitable sulfur content present a better performance. The first discharge capacity of this composite reaches 1401â
mAhâgâ1 at 0.2â
C. Even after 200â
cycles, the discharge capacity remains at 626â
mAhâgâ1
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Layered oxychalcogenides: structural chemistry and thermoelectric properties
Layered oxychalcogenides have recently emerged as promising thermoelectric materials. The alternation of ionic oxide and covalent chalcogenide layers found in these materials often results in interesting electronic properties, and also facilitates the tuning of their properties via chemical substitution at both types of layers. This review highlights some common structure types found for layered oxychalcogenides and their interrelationships. This review pays special attention to the potential of these materials for thermoelectric applications, and provides an overview of the thermoelectric properties of materials of current interest, including BiCuSeO
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