Controlled synthesis of mesoporous carbon nanosheets and their enhanced supercapacitive performance

Mesoporous carbon nanosheets (MCNs) were synthesized using porous magnesium oxide (MgO) layer as the template precursor and resol as the carbon source. The morphology of the mesoporous carbon particles can be easily controlled by altering the mass ratio of MgO to resol. The structural characterization demonstrates that the interlaced MCNs can be formed when MgO/resol is 1:1 and they possess the carbon nanolayer with a thickness of about 5 nm and a width of about 200 nm. The quantities of mesopores and micropores endow the MCNs with a large surface area of 1,180 m²?g^?1 and a high pore volume of 1.56 cm³?g^?1. The supercapacitive performance of carbon products synthesized with various MgO/resol ratios was evaluated using cyclic voltammetry and galvanostatic charge–discharge techniques. The results show that the interlaced MCNs exhibit the highest specific capacitance of 241 F?g^?1, the best rate capability and cycling stability, which are attributed to the fast electrolyte ion transport or diffusion throughout the electrode matrix and effective utilization of the electrical double-layer capacitance of carbon layer.     

Anchoring cobalt single atoms on 2D covalent triazine framework with charge nanospatial separation for enhanced photocatalytic pollution degradation

Covalent triazine frameworks (CTFs) show great potential in photocatalytic fields, while their practical efficiency is still limited due to rapid charge recombination. Here we report a nanospatial separation strategy for photoinduced electron-hole pairs of CTF-1 nanosheets via single-atom Co using facile pyrolysis and phosphorization to form stable Co–N₃ (≈1.60 Å) architecture. HAADF-STEM image demonstrates Co atoms are uniformly dispersed onto ultrathin CTF-1. The local structure surrounding and chemical valent state of Co are systematically investigated by Fourier-transformed EXAFS and K-edge XANES, respectively. Co single atoms as oxidation centers can capture holes transferred from CTF-1, thus resulting in narrow bandgap and improved photo-exciton dissociation in the two-dimensional (2D) direction. The obtained Co/CTF-1 exhibits excellent efficiency of 99.9% for pollutant photodegradation, far outperforming that of pristine CTF-1 (68.8%). Nanospatial separation endows Co/CTF-1 with various micropollution removal capabilities, outstanding cyclic stability, and a widely effective pH range (1.0–11.0) under visible light. Furthermore, active oxidating radicals of h⁺ and ?O₂^? are dominant in photocatalytic degradation for various organic contaminants. This study motivates the atomic design and fabrication of 2D photocatalysts with excellent charge nanospatial separation.     

Electrochemical supercapacitive performance of potentiostatically cathodic electrodeposited nanostructured MnO2 films

Journal of Solid State Electrochemistry - Nanostructured MnO2 films were prepared via cathodic electrodeposition under potentiostatic condition. X-ray diffraction (XRD) analyses reveal that the...     

Simple synthesis of novel phosphate electrode materials with unique microstructure and enhanced supercapacitive properties

Flower-like Ni₃P₂O₈ and flower-like Fe₃P₂O₈·8H₂O have been successfully synthesized by a simple chemical precipitation method.X-ray diffraction（XRD） patterns reveal an amorphous phase formation of nickel phosphate（Ni₃P₂O₈） and pure monoclinic phase of Fe₃P₂O₈·8H₂O.The novel flower-like Ni₃P₂O₈ and flower-like Fe₃P₂O₈·8H₂O when used for supercapacitor electrode materials exhibit a high specific capacitance（C m） of 1464 F/g and 200 F/g at a current density of 0.5 A/g,respectively.Eventually,an asymmetric supercapacitor is fabricated using Ni₃P₂O₈ as positive electrode and Fe₃P₂O₈·8H₂O as negative electrode.A high specific capacitance of 94 F/g is achieved in the high-voltage region of 0 ～1.6 V,and a large energy density of 32.6 Wh/kg is delivered at power density of 420 W/kg.The findings demonstrate the important and great potential of developing metal phosphate based materials for supercapacitors.     

Nitridation-induced metal-organic framework nanosheet for enhanced water oxidation electrocatalysis

We report the synthesis of nitridation-induced NiFe-MOF through post-synthetic functionalization of terminal ligand in NiFe-MOF nanosheet.We directly identify the key factor of amino ligand in N-NiFe-MOF for boosting the OER performance through combining single X-ray crystallographic characterization and in-situ Raman tracking,as well as ex-situ spectroscopy analysis.Density functional theory(DFT)calculations and experime ntal results indicate irreversible phase rec on structio n from amino ligand oxidation prior to OER could lead to the optimized ΔG_-O,resulting in the remarkable OER performance with an overpotential of 258 mV to obtain the current density of 100 mA cm^-2 in 1.0 M KOH solution.Our work will provide new strategy for rational designing advanced MOF-based OER electrocatalysts.     

Sample introduction into ICP-OES for metallic samples

Two different methods of sample introduction into an ICP source have been applied to solve special problems of metal analysis. First, an electrolytical cell was used to dissolve the metallic compounds of metals only. The resulting analyte solution is flow-injected directly into the ICP. Secondly, the solid sampling by a graphite crucible heated up temperature-controlled and coupled directly to the ICP torch system was modified to determine 9 trace elements contained in 24 available certified reference samples.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria     

The discovery of interfacial electronic interaction within cobalt boride@MXene for high performance lithium-sulfur batteries

Lithium-sulfur battery is strongly considered as the most promising next-generation energy storage system because of the high theoretical specific capacity.The serious "shuttle effect" and sluggish reaction kinetic limited the commercial application of lithium-sulfur battery.Many hetero structure s were applied to accelerate polysulfides conversion and suppress their migration in lithium-sulfur batteries.Nevertheless,the effect of the interface in heterostructure was not clear.Here,the Co_2B@MXene heterostructure is synthesized through chemical reactions at room temperature and employed as the interlayer material for Li-S batteries.The theoretical calculations and experimental results indicate that the interfacial electronic interaction of Co_2B@MXene induce the transfer of electrons from Co_2B to MXene,enhancing the catalytic ability and favoring fast redox kinetics of the polysulfides,and the theoretical calculations also reveal the underlying mechanisms for the electron transfer is that the two materials have different Fermi energy levels.The cell with Co_2B@MXene exhibits a high initial capacity of1577 mAh/g at 0.1 C and an ultralow capacity decay of 0.0088% per cycle over 2000 cycles at 2 C.Even at5.1 mg/cm~2 of sulfur loading,the cell with Co_2B@MXene delivers 5.2 mAh/cm~2 at 0.2 C.     

Influence of synthesis temperature on cobalt metal-organic framework (Co-MOF) formation and its electrochemical performance towards supercapacitor electrodes

Journal of Solid State Electrochemistry - We have synthesized cobalt metal-organic framework (Co-MOF) at different temperatures through solvothermal route as metal-organic frameworks which can be...     

Needle-like cobalt phosphide arrays grown on carbon fiber cloth as a binder-free electrode with enhanced lithium storage performance

Cobalt phosphide(CoP) is a promising anode candidate for lithium-ion batteries(LIBs) due to its high specific capacity and low working potential.However,the poor cycling stability and rate performance,caused by low electrical conductivity and huge volume variation,impede the further practical application of CoP anode materials.Herein,we report an integrated binder-free electrode featuring needle-like CoP arrays grown on carbon fiber cloth(CC) for efficient lithium storage.The as-prepared CoP/CC electrode integrates the advantages of 1 D needle-like CoP arrays for efficient electrolyte wettability and fast cha rge transpo rtation,and 3 D CC substrate for superior mechanical stability,flexibility and high conductivity.As a result,the CoP/CC electrode delivers an initial specific capacity of 1283 mAh/g and initial Coulombic effeciencies of 85.4%,which are much higher than that of conventional CoP electrode.Notably,the Co P/CC electrode shows outstanding cycling performance up to 400 cycles at 0.5 A/cm² and excellent rate performance with a discharge capacity of 549 mAh/g even at 5 A/cm².This work demonstrates the great potential of integrated CoP/CC hybrid as efficient bind-free and freestanding electrode for LIBs and future flexible electronic devices.     

Fabrication and supercapacitive performance of long anodic TiO2 nanotube arrays using constant current anodization

A galvanostatic anodization is used to prepare long TiO₂ nanotube arrays (TNTAs). TNTAs of over 100 μm in length, with similar nanotube size and structural regularity to the classic TNTAs made from potentiostatic mode, are achieved at 10 mA cm^− 2. After a post-anodization in a H₃PO₄-based electrolyte, the TNTAs with long nanotubes exhibit good adhesion to Ti substrate. The as-prepared long TNTAs yield a larger areal capacitance of 128.4 mF cm^− 2. Further, the long TNTAs possess a higher surface area, making them suitable as support templates for other active materials.     

Improved supercapacitive performance of low pore size and highly stable nanostructured NiCo2O4 electrodes

Journal of Solid State Electrochemistry - The nanostructured nickel cobaltite has been synthesized by a cost-effective facile hydrothermal method and demonstrated excellent electrochemical...     

In situ Sn-doped WO3 films with enhanced photoelectrochemical performance for reducing CO2 into formic acid

Journal of Solid State Electrochemistry - We report exploiting effective Sn incorporation to enhance the photoelectrochemical activity of WO3 plate films, applied as photoanodes for...     

Hollow Fe2O3/Co3O4 microcubes derived from metal-organic framework for enhanced sensing performance towards acetone

In this work, hollow Fe₂O₃/Co₃O₄ microcubes have been successfully synthesized through a hydrothermal method followed by an annealing process using metal-organic framework of Prussian blue as a soft template. The morphologies, microstructures, surface area and element compositions have been carefully characterized by a series of techniques. Meanwhile, compared with that of pure Fe₂O₃ and Co₃O₄, the gas sensor based on the hollow microcubes exhibits enhanced sensing performances towards acetone, e.g., a higher response of 21.2 and a shorter response time of 5 s towards 20 ppm acetone at a relatively low working temperature of 200 °C. Moreover, the hollow microcubes-based gas sensor still shows perfect long-term stability, excellent repeatability and the ability of sub-ppm level detection, which provides a possibility for its application in real life. The enhanced gas sensing performances can be attributed to the hollow structure with a high surface area and the formed p-n heterojunctions within the microcubes.     

Synthesis and performance evaluation of novel cobalt hydroxychlorides for electrochemical supercapacitors

Co₂(OH)₃Cl has been prepared by a facile one pot sol-gel process. Two different solvents, ethylene glycol and glycerol, are used for the synthesis. The resulting samples are studied for their morphology, structure, and electrochemical stability upon cycling. The sample with ethylene glycol as solvent exhibits three-dimensional porous interconnected xerogel morphology, whereas that with glycerol shows a crystalline and non-porous nanoparticulate structure. The specific capacitance of the Co₂(OH)₃Cl prepared with ethylene glycol is 434 F/g, when the electrodes are cycled in 3 M KOH at a specific current 2 A/g, and with that of glycerol, it is 252 F/g. Interestingly, at a high current density of 25 A/g, Co₂(OH)₃Cl with ethylene glycol and glycerol showed 143 and 72 F/g, respectively. Ethylene glycol significantly modified the structure and morphology so as to attain a mesoporous Co₂(OH)₃Cl with high surface area, which in turn influenced its remarkable electrochemical behavior. With a significant specific capacity and electrochemical stability, the synthesized material is a novel potential candidate for supercapacitors.