Project description:MXene is investigated as an electrode material for different energy storage systems due to layered structures and metal-like electrical conductivity. Experimental results show MXenes possess excellent cycling performance as anode materials, especially at large current densities. However, the reversible capacity is relatively low, which is a significant barrier to meeting the demands of industrial applications. This work synthesizes N-doped graphene-like carbon (NGC) intercalated Ti3C2Tx (NGC-Ti3C2Tx) van der Waals heterostructure by an in situ method. The as-prepared NGC-Ti3C2Tx van der Waals heterostructure is employed as sodium-ion and lithium-ion battery electrodes. For sodium-ion batteries, a reversible specific capacity of 305 mAh g-1 is achieved at a specific current of 20 mA g-1, 2.3 times higher than that of Ti3C2Tx. For lithium-ion batteries, a reversible capacity of 400 mAh g-1 at a specific current of 20 mA g-1 is 1.5 times higher than that of Ti3C2Tx. Both sodium-ion and lithium-ion batteries made from NGC-Ti3C2Tx shows high cycling stability. The theoretical calculations also verify the remarkable improvement in battery capacity within the NGC-Ti3C2O2 system, attributed to the additional adsorption of working ions at the edge states of NGC. This work offers an innovative way to synthesize a new van der Waals heterostructure and provides a new route to improve the electrochemical performance significantly.
Project description:Cu2Se with high theoretical capacity and good electronic conductivity have attracted particular attention as anode materials for sodium ion batteries (SIBs). However, during electrochemical reactions, the large volume change of Cu2Se results in poor rate performance and cycling stability. To solve this issue, nanosized-Cu2Se is encapsulated in 1D nitrogen-doped carbon nanofibers (Cu2Se-NC) so that the unique structure of 1D carbon fiber network ensures a high contact area between the electrolyte and Cu2Se with a short Na+ diffusion path and provides a protective matrix to accommodate the volume variation. The kinetic analysis and DNa+ calculation indicates that the dominant contribution to the capacity is surface pseudocapacitance with fast Na+ migration, which guarantees the favorable rate performance of Cu2Se-NC for SIBs.
Project description:As a promising energy storage system, potassium (K) ion batteries (KIBs) have received extensive attention due to the abundance of potassium resource in the Earth's crust and the similar properties of K to Li. However, the electrode always presents poor stability for K-ion storage due to the large radius of K-ions. In our work, we develop a nitrogen-doped carbon nanofiber (N-CNF) derived from bacterial cellulose by a simple pyrolysis process, which allows ultra-stable K-ion storage. Even at a large current density of 1 A g-1, our electrode exhibits a reversible specific capacity of 81 mAh g-1 after 3000 cycles for KIBs, with a capacity retention ratio of 71%. To investigate the electrochemical enhancement performance of our N-CNF, we provide the calculation results according to density functional theory, demonstrating that nitrogen doping in carbon is in favor of the K-ion adsorption during the potassiation process. This behavior will contribute to the enhancement of electrochemical performance for KIBs. In addition, our electrode exhibits a low voltage plateau during the potassiation-depotassiation process. To further evaluate this performance, we calculate the "relative energy density" for comparison. The results illustrate that our electrode presents a high "relative energy density", indicating that our N-CNF is a promising anode material for KIBs.
Project description:Potassium-ion batteries (KIBs) have great potential for applications in large-scale energy storage devices. However, the larger radius of K+ leads to sluggish kinetics and inferior cycling performance, severely restricting its practical applicability. Herein, we propose a rational strategy involving a Prussian blue analogue-derived graphitized carbon anode with fast and durable potassium storage capability, which is constructed by encapsulating cobalt nanoparticles in nitrogen-doped graphitized carbon (Co-NC). Both experimental and theoretical results show that N-doping effectively promotes the uniform dispersion of cobalt nanoparticles in the carbon matrix through Co-N bonds. Moreover, the cobalt nanoparticles and strong Co-N bonds synergistically form a three-dimensional conductive network, increase the number of adsorption sites, and reduce the diffusion energy barrier, thereby facilitating the adsorption and the diffusion kinetics. These multiple effects lead to enhanced reversible capacities of 305 and 208.6 mAh g-1 after 100 and 300 cycles at 0.05 and 0.1 A g-1, respectively, demonstrating the applicability of the Co-NC anode for KIBs.
Project description:Sodium ion batteries (SIBs) have been considered as a promising alternative to lithium ion batteries (LIBs) for large scale energy storage in the future. However, the commercial graphite anode is not suitable for SIBs because of its low Na+ ions storage capability and poor cycling stability. Recently, another alternative as anode for SIBs, amorphous carbon materials, have attracted tremendous attention because of their abundant resource, nontoxicity, and most importantly, stability. Here, N-doped hierarchical porous carbon microspheres (NHPCS) derived from Ni-MOF have been prepared and used as anode for SIBs. Benefiting from the open porous structure and expanded interlayer distance, the diffusion of Na+ is greatly facilitated and the Na+ storage capacity is significantly enhanced concurrently. The NHPCS exhibit high reversible capacity (291 mA h g-1 at current of 200 mA g-1), excellent rate performance (256 mA h g-1 at high current of 1,000 mA g-1), and outstanding cycling stability (204 mA h g-1 after 200 cycles).
Project description:Sodium ion batteries have drawn extensive attentions for large-scale energy storage to replace lithium ion batteries primarily due to the natural abundance of sodium resource and low cost, but their energy density and electrochemical performance are hindered by the sluggish diffusion kinetics of sodium ion. Herein, free-standing nitrogen-doped graphene aerogel has been fabricated via hydrothermal reaction as the potential anode material for sodium ion batteries. The three dimensional porous network structure of the graphene aerogel provides sufficient interstitial space for sodium ion accommodation, allowing fast and reversible ion intercalation/de-intercalation. The nitrogen doping could introduce defects on the graphene sheets, making the feasible transport of large-sized sodium ion. Benefiting from the effective structure and nitrogen doping, the obtained material demonstrates high reversible capacities, good cycling performance (287.9 mA h g-1 after 200 cycles at a current density of 100 mA g-1), especially superior rate capability (151.9 mA h g-1 at a high current density of 5 A g-1).
Project description:Potassium-ion batteries (PIBs) are attractive for grid-scale energy storage due to the abundant potassium resource and high energy density. The key to achieving high-performance and large-scale energy storage technology lies in seeking eco-efficient synthetic processes to the design of suitable anode materials. Herein, a spherical sponge-like carbon superstructure (NCS) assembled by 2D nanosheets is rationally and efficiently designed for K+ storage. The optimized NCS electrode exhibits an outstanding rate capability, high reversible specific capacity (250 mAh g-1 at 200 mA g-1 after 300 cycles), and promising cycling performance (205 mAh g-1 at 1000 mA g-1 after 2000 cycles). The superior performance can be attributed to the unique robust spherical structure and 3D electrical transfer network together with nitrogen-rich nanosheets. Moreover, the regulation of the nitrogen doping types and morphology of NCS-5 is also discussed in detail based on the experiments results and density functional theory calculations. This strategy for manipulating the structure and properties of 3D materials is expected to meet the grand challenges for advanced carbon materials as high-performance PIB anodes in practical applications.
Project description:Dehydrogenation of (partially) saturated heterocycles provides an important route to heteroaromatic compounds. A heterogeneous cobalt oxide catalyst, previously employed for aerobic oxidation of alcohols and amines, is shown to be effective for aerobic dehydrogenation of various 1,2,3,4-tetrahydroquinolines to the corresponding quinolines. The reactions proceed in good yields under mild conditions. Other N-heterocycles are also successfully oxidized to their aromatic counterparts.
Project description:Nonaqueous Na-ion capacitors (NICs) have been recently regarded as potential sustainable power devices due to their high specific energy/power and the abundant distribution of sodium resources on the Earth. However, the power performance of current NICs is usually restricted by the kinetics imbalance between sodium deintercalation/intercalation in the anode and surface ion adsorption/desorption in the cathode. Herein, we demonstrate superior sodium-ion storage properties of nitrogen/sulfur co-doped hierarchical hollow carbon nanofibers (N/S-HCNFs) for their application as an ideal anode material for NICs. The N/S-HCNFs are fabricated through in situ gas sulfuration of a hollow polyaniline nanofiber precursor, which is obtained with the aid of citric acid templates. Benefiting from the positive synergistic effects of both N and S co-doping in carbon and the hierarchical hollow one-dimensional structure, the sodium-storage performance of N/S-HCNFs half-cell versus Na/Na+ exhibits a high capacity (∼447 mA h g-1 at 50 mA g-1), excellent rate capability (∼185 mA h g-1 at 10 A g-1), and outstanding cycling stability (no capacity decay after 3000 cycles at 5 A g-1), which is among the best sodium-ion storage performances of carbonaceous Na-storage anodes. Furthermore, a dual-carbon NIC device is constructed with N/S-HCNFs as an anode and activated carbon (AC) as a cathode, and it has a large energy density of 116.4 W h kg-1, a high power density of 20 kW kg-1 (at 48.2 W h kg-1) and a long cycle life of 3000 cycles, which is superior to most reported AC-based NICs.
Project description:Nitrogen incorporated carbon materials play an important role in electrochemical energy conversion technologies from fuel cells to capacitive storage devices. This work investigates the effects of nitrogen incorporation on capacitance, work function and semiconductor properties of amorphous carbon thin film electrodes. Nitrogenated electrodes (a-C:N) electrodes were synthesized via magnetron sputtering and characterized using X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy (UPS), Raman spectroscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). EIS was carried in both aqueous (0.1 M KCl) and organic (0.1 M TBAPF6/acetonitrile) electrolytes to discriminate between pseudocapacitive contributions and changes to semiconductor properties of the materials arising from structural and chemical disruption of the graphitic carbon scaffold. Raman and UPS spectroscopy both suggest that nitrogen incorporation increases the metallic character of the disordered carbon matrix at low-intermediate concentrations, whereas further nitrogen incorporation results in significantly more defective carbon with small graphitic cluster size. EIS studies in 0.1 M KCl indicate that the capacitance of a-C:N electrodes increases relative to nitrogen-free a-C electrodes due to a combination of microroughness and pseudocapacitive contributions in parallel to those of the double layer capacitance. Results in 0.1 M TBAPF6 in acetonitrile which are dominated by the interfacial capacitance, show that initial nitrogen incorporation into the disordered carbon scaffold compensates for p-type properties in the disordered carbon matrix, resulting in an increase in metallic character. Greater levels of nitrogenation, are instead disruptive and increase defect density while decreasing the double layer capacitance.