Nitrogen-doped micropores binder-free carbon-sulphur composites as the cathode for long-life lithium-sulphur batteries

Nitrogen-doped micropores-contained carbon nanofibres (NMCNFs) were prepared by carbonizing ZIF-8 grown in liquid-phase along with electrospinning. When NMCNFs act as sulphur host materials in lithium–sulphur batteries, NMCNFs can retard the shuttle effect and dissolution of polysulfides through the synergic action of effective physical confinement to micropores and nitrogen surface chemical absorption. NMCNFs show a capacity up to 636 mAh g−1 after 500 cycles against Li anode

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 g−1 and a pore volume of up to 1.29 cm3 g−1, 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 g−1 at a current density of 0.5 A g−1 in a three-electrode system. The results also reveal a high-rate capacitance (72.2% capacitance retention at 500 mV s−1) and stable cycling lifetime (95% of initial capacitance after 15 000 cycles). Moreover, CsCNBs*4 provides a high energy density of 29.8 W h kg−1 at a power density of 345.4 W kg−1 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

A universal strategy to prepare sulfur-containing polymer composites with desired morphologies for lithium−sulfur batteries

Lithium–sulfur (Li–S) batteries are probably the most promising candidates for the next-generation batteries owing to their high energy density. However, Li–S batteries face severe technical problems where the dissolution of intermediate polysulfides is the biggest problem because it leads to the degradation of the cathode and the lithium anode, and finally the fast capacity decay. Compared with the composites of elemental sulfur and other matrices, sulfur-containing polymers (SCPs) have strong chemical bonds to sulfur and therefore show low dissolution of polysulfides. Unfortunately, most SCPs have very low electron conductivity and their morphologies can hardly be controlled, which undoubtedly depress the battery performances of SCPs. To overcome these two weaknesses of SCPs, a new strategy was developed for preparing SCP composites with enhanced conductivity and desired morphologies. With this strategy, macroporous SCP composites were successfully prepared from hierarchical porous carbon. The composites displayed discharge/charge capacities up to 1218/1139, 949/922, and 796/785 mA h g–1 at the current rates of 5, 10, and 15 C, respectively. Considering the universality of this strategy and the numerous morphologies of carbon materials, this strategy opens many opportunities for making carbon/SCP composites with novel morphologies

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 g−1) and large pore volume (up to 1.29 cm3 g−1) 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 g−1 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 g−1) 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

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 (14.23 wt%) and high specific surface area (942 m2 g−1) by 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 272 F g-1 at 0.1 A g−1, 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 154 F g-1 at 0.1 A g−1. 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 2949 m2 g−1 and pore volume up to 2.9 cm3 g−1 were successfully synthesized from polyaniline‐co‐polypyrrole 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 lithium‐sulfur 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 1401 mAh g−1 at 0.2 C. Even after 200 cycles, the discharge capacity remains at 626 mAh g−1

CoSe2/Co nanoheteroparticles embedded in Co, Nco-doped carbon nanopolyhedra/nanotubes as anefficient oxygen bifunctional electrocatalyst for Zn–air batteries

Transition metal selenide-based materials have been demonstrated as promising electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), yet the actual design of a highly efficient and stable electro-catalyst based on these materials still remains a long and arduous challenge. Herein, a predesigned hybrid Zn/Co zeolitic imidazole framework was used to fabricate CoSe2/Co nanoheteroparticles embedded within hierarchically porous Co, N co-doped carbonnanopolyhedra/nanotubes (CoSe2/Co@NC-CNTs) through a facile approach involving controlled carbonization and selenization procedures. As expected, the optimized CoSe2/Co@NC-CNT-1 displayed outstanding electrocatalytic performance for the ORR and OER, with an onset potential of 0.95 V vs. RHE, a half-wave potential of 0.84 V vs. RHE for ORR, and a potential of 1.69 V vs. RHE for OER at 10 mA cm−2. It also exhibited excellent long-term stability and methanol resistance ability, which were superior to commercial IrO2 and the commercial 20 wt% Pt/C catalyst. Notably, the assembled Zn–air battery with CoSe2/Co@NC-CNT-1 showed a low charge–discharge voltage gap (0.696 V at 10 mA cm−2) and a high peak power density (100.28 mW cm−2) with long-term cycling stability. These superior performances can be ascribed to the synergistic effects of the highly active CoSe2/Co nanoheterostructure, hierarchically porous structure with a large surface area, high electrical conductivity and uniform doping of the Co and

Facile synthesis of 2D ultrathin and ultrahigh specific surface hierarchical porous carbon nanosheets for advanced energy storage

Two dimensional (2D) porous carbon nanosheets (CNS) have attracted tremendous research interests in energy storage and conversion, such as supercapacitors (SCs) and lithium-sulfur batteries, because of their unique micromorphology, chemical stability and high specific surface area (SSA). Rational design and facile scalable synthesis of CNS with high SSA, low cost and ultrathin nanosheet structure is highly desired but hitherto remains a big challenge. Here, we report a novel synthesis method of 2D hierarchical porous CNS with ultrahigh SSA (2687 m2 g−1) and ultrathin structure by directly pyrolysing and activating a unique and abundant biomass sheet. The electrochemical characterisations show that the prepared CNS-4-1 materials as electrodes creates a good energy-storage capability, with the energy density being 91 Wh kg−1 for symmetric SCs in ionic liquids, which is the highest in the reported biomass-derived CNS materials for SCs applications so far. Besides, the CNS-5-1 also exhibits a high initial capacity of 1078 mAh g−1 at 0.1 C when it acted as a sulfur hosting material for lithium-sulfur batteries. More importantly, it also shows a 586 mAh g−1 reversible capacity and an approaching 100% coulombic efficiency after 500 cycles at a high rate of 1 C. These superior electrochemical properties of the CNS are mainly attributed to their unique 2D ultrathin nanosheet structure, large SSA, and reasonable hierarchical porous structure. This work not only provides a new strategy to fabricate the ultrathin CNS in large scale and low cost but also enlarges CNS materials potential applications in energy storage

High entropy materials for oxygen electrocatalysis

Oxygen electrocatalysis, including the oxygen evolution and reduction, is the key part in the energy framework with hydrogen as an energy carrier. However, current oxygen electrocatalysts cannot meet the highly efficient conversion between chemical energy (electrolyzer) and electricity (hydrogen fuel cells). Thus, developing high efficient, stable and low-cost oxygen electrocatalyst is the main challenge. High-entropy materials offer a new perspective on developing advanced oxygen electrocatalysts because of synergy effects among multiple components, offering possibilities to break the property limits of traditional materials in the catalysis field. Here, this research, with the research targets of high-entropy materials, aims to develop new oxygen electrocatalysts for oxygen evolution and reduction reaction, and try to solve the issues in oxygen electrocatalysts mentioned above.Due to four-electron transfer, the oxygen evolution reaction (OER) results in sluggish reaction kinetics, thereby challenging the development of advanced electrolyzer technologies. Ruthenium and iridium-based materials have been recognized as good catalysts in the OER, but their high cost and scarcity impede large-scale applications of electrolyzers.Thus, given the above consideration, the first part of this thesis focuses on fabricating new low-cost OER catalysts and understanding the relationship between their physical properties and OER activity. More specifically, highentropy metal-organic frameworks (HEMOFs) OER catalysts were synthesized by introducing multi-metal nodes into single metal MOFs. Based on this type of OER catalyst, three main questions are thus addressed, namely i) the influence on electronic structures when introducing multi-metal nodes into MOFs, ii) identifying possible metal catalytic sites in HEMOFs and iii) the main factors affecting the electrocatalytic activity of prepared catalysts. Moreover, the optimized Co-Rich-HEMOFs has an overpotential of 310 mV and a current density of 38 mA cm-2 at 1.6 V vs. RHE.The second part is to develop new electrocatalysts for the oxygen reduction reaction (ORR), a bottleneck reaction where chemical energy is converted into electricity in hydrogen fuel cells. In this part, a new facile method combining a solid-state thermal reaction and a carbonization process is employed to synthesize high-entropy alloys (HEAs) encapsulated in hollow carbon tubes, thereby breaking the limitations associated with the wet-chemistry method. The leading research can be divided as follows. First, the synthesis parameters of the catalyst were optimized, including carbonization temperature, as well as the ratio of organic carbon sources and introduced metal elements. Second, ORR activity was measured by electrochemical analytical techniques performed in 0.1 M KOH. The influence of crystal structure, specific surface area (SSA) and degree of graphitization on ORR activity was analyzed. Moreover, the in situ X-ray diffraction method was used to study the HEA formation process, such as the observed formation temperature of HEAs (908 K). Finally, electrochemical tests indicate that the optimized HEAs can maintain a 100% current after 10 hours of operation, revealing good stability in ORR.The third part focuses on understanding the effects of particle size and metal-rich types on ORR activity for HEA catalysts based on the method developed in the second part. More specifically, by changing the introduced transition metal content (Mn, Fe, Co and Ni), HEA particle sizes can be tailored. The electrochemical results reveal that particle size and metal-rich types affect ORR activity. Specifically, the HEAs with small particle size and Fe-rich type tend to obtain good ORR activity. In addition, the difference in terms of catalytic activity between HEAsand single metal particles by using Fe in the control samples is investigated. The electrochemical result reveals that Fe-Rich-HEAs(1-16) ensures good performance with an E1/2 of 0.861 V vs. RHE in a 0.1 M KOH solution. These findings offer new references for fabricating new oxygen electrocatalysts and illustrate the potential application of high-entropy materials in catalysis field.<br/