Two new ant species of the genus Leptogenys (Hymenoptera, Formicidae) from Hainan, China, with a key to the known Chinese species.

Two new species of ponerine ants from Hainan Province, China, Leptogenyshainanensissp. nov. and L.zhouisp. nov., are delineated and depicted based on the worker caste. Leptogenyshainanensissp. nov. belongs to the L.leleji species group, with mandibles elongate, slender and curved, lacking a distinct masticatory margin. On the other hand, L.zhouisp. nov. belongs to the L.crassicornis species group, distinguished by its square head, smooth body, mandibles with a dentate masticatory margin, and short antennae. A key to workers for the known species of Leptogenys in China are provided and a map is provided for the newly described species.

Electrolyte additive strategy enhancing the electrochemical performance of a soft-packed LiCoO2//graphite full cell.

During the development of high-capacity, ultra-stable battery electrode materials, battery performance, and safety issues are proved to be related to the properties of the electrolyte used. The employment of electrolyte additives is to improve the battery electrolyte properties. Representative commercial two-electrode LiCoO2//graphite pouch cells are used to study electrolyte additives represented by fluoroethylene carbonate (FEC) to improve the electrochemical stability of a commercial pouch full cell. The study reveals that a 1.5% FEC electrolyte additive has the best stability in the voltage range of 3.0-4.2 V.

Unveiling the promotion of intermediates transport kinetics on the N/S co-doping 3D structure titanium carbide aerogel for high-performance supercapacitors.

Two-dimensional (2D) transition metal carbides (MXene) have shown great advantages as electrode materials in the new generation of energy storage, especially in supercapacitors. However, the inherent low specific capacitance and restacking layers of nanosheets that occur during electrode preparation further reduce the electrochemical performance of the materials. Based on this, we design a N, S co-doping electrode with a three-dimensional (3D) structure, which not only improves the specific capacitance through fundamentally modifying the electronic structure of the electrode materials, but also effectively improves the rate performance of the electrode by preventing the restacking of 2D materials. The N, S co-doping 3D architecture Ti3C2Tx electrode (TC/NS-3D) exhibits an excellent capacitance value of 440 F g-1 at 5 mV s-1 and 64% capacitance retention rate at a high scan rate of 1000 mV s-1 in 3 mol L-1 H2SO4 electrolyte. The TC/NS-3D electrode also shows excellent capacitance retention of 97.2% after the 10,000 cycles stability test. The density functional theory (DFT) analysis reveals the enhanced performance is attributed to accelerated intermediates transport kinetics promoted by 3D structure engineering and N, S co-doping for Ti3C2Tx. This study is promising in designing heteroatomic doping 3D structure MXene-based materials for electrochemical energy storage systems.

Understanding the Different Diffusion Mechanisms of Hydrated Protons and Potassium Ions in Titanium Carbide MXene.

The high intercalation capacitance of MXenes is attractive, but their performance as electrodes in supercapacitors is limited by mass transport when increasing the thickness and mass loading of the electrodes. Here, we report a combined experimental and computational study, through which we reveal the diffusion of hydrated ionic species at the interlayer spaces. We find that the cyclic voltammetry (CV) curves for the delaminated Ti3C2T x exhibit distinct features in acid (H2SO4) and alkaline (KOH) electrolytes. The calculated migration profiles of K+ and H+ using density functional theory, in the presence and absence of water, suggest that the intercalated water molecules stabilize the charged ions, facilitating their diffusion from two dimension to three dimension manifested by reduced activation barriers and movement pathways. In addition, we show that the diffusion of low and high concentrations of protons is significantly different; that is, protons of high concentrations can be adsorbed at both sides of the interlayer spaces, and water drives frequent proton hopping between stable adsorption sites as shown in the ab initio molecular dynamics simulations. The calculations can thus explain the varied capacitance and distorted CV curves when the experiments are conducted in acid and alkaline electrolytes. These results can provide guidance for improving the fast transport of ions and electrons in MXenes with high mass loading.

3D Ti3C2Tx aerogels with enhanced surface area for high performance supercapacitors.

Two-dimensional titanium carbide as a novel electrode material has been widely researched in the field of energy storage in recent years. However, the restacking of Ti3C2Tx nanosheets is still a challenge, which largely restricts their development. Here, we employ the 3D architecture of a Ti3C2Tx aerogel to restrict the restacking of 2D Ti3C2Tx nanosheets. This special structure can not only effectively reduce the restacking of 2D materials, but also accelerate the transport of electrolyte ions in the electrode. The as-prepared Ti3C2Tx aerogel possessed a large special surface area of 108 m2 g-1 and achieved a special capacitance of 349 F g-1 which is retained even at a high scan rate of 2000 mV s-1 in the 3 M H2SO4 electrolyte, indicating an ultrahigh rate capability. Moreover, at a higher current density of 20 A g-1, 90% of the initial capacitance is also retained after 20 000 charging-discharging cycles, revealing an excellent cycling stability. Furthermore, the mechanism of charge storage was investigated.

Self-assembled Ti3C2Tx/SCNT composite electrode with improved electrochemical performance for supercapacitor.

Two-dimensional titanium carbide has gained considerable attention in recent years as an electrode material for supercapacitors due to its high melting point, good electrical conductivity, hydrophilicity and large electrochemically active surfaces. However, the irreversible restacking during synthesis restricts its development and practical applications. Here, Ti3C2Tx/SCNT self-assembled composite electrodes were rationally designed and successfully synthesized by introducing single-walled carbon nanotubes (SCNTs) as interlayer spacers to decrease the restacking of the Ti3C2Tx sheets during the synthesis process. SCNTs can not only increase the specific surface area as well as the interlayer space of the Ti3C2Tx electrode, but also increase the accessible capability of electrolyte ions, and thus it improved the electrochemical performance of the electrode. The as-prepared Ti3C2Tx/SCNT self-assembled composite electrode achieved a high areal capacitance of 220mF/cm2 (314F/cm3) and a remarkable capacitance retention of 95% after 10,000cycles.