Superior Electrochemical Behavior Research Articles

Cubic Prussian blue crystals from a facile one-step synthesis as positive electrode material for superior potassium-ion capacitors

Cubic Prussian blue (PB) crystals are prepared by a facile one-step synsthesis. The structure and morphology of the as-prepared samples are characterized by X-ray power diffraction, inductively coupled plasma, scanning electron microscopy and electrochemical measurement. The PB electrode exhibits superior electrochemical behavior in K2SO4 aqueous solution including high reversible capacity (80 mAh g−1 at the current density of 0.5 A g−1), outstanding rate capability and good cycling stability. The K-ion capacitor (KIC) is also fabricated by using PB as a positive electrode and commercial activated carbon as an negative electrode, and it presents a maximum energy density of 28 Wh kg−1 at the current density of 1 A g−1 (corresponding to 7.5mA cm−2). Furthermore, the KIC also exhibits excellent cycling stability at the current density of 2 A g−1 with capacity retention of nearly 98% over 1200 cycles. Our synthesized electrode material provides a new way for fabricating high performance electrode materials for superior KIC.

Nano-glass ceramic cathodes for Li+/Na+ mixed-ion batteries

Abstract Electrode materials can display superior electrochemical performances and behavior via the nanoscale design. Here, the low-temperature synthesis of nano-glass ceramics (NGCs) is based on inheriting the network structure of yeast polyphosphate metabolism. The NGCs-3 sample synthesized with a molar ratio of Fe/V = 7:6 is composed of nano-domains of semiconducting oxide glass (Li 2 O-Na 2 O-Fe 2 O 3 -V 2 O 5 -P 2 O 5 , LNFVP), nanocrystalline particles (Li 9 Fe 3 P 8 O 29 , Li 0.6 V 1.67 O 3.67 and VOPO 4 ), and nanopores connected by interfaces. We have clarified the mixing ion transport mechanism and the electrochemical reactions, and the influences of molar ratio of Fe/V on the structure and electrochemical properties of NGCs. This nanoscale design offers a new possibility improved the electrochemical performances of Li + /Na + mixed-ion batteries (LNMIBs). The NGCs-3 electrode exhibits a higher discharge capacity (145 mAh g −1 ) and energy storage density (525 Whkg −1 ) at 5C, and the capacity retention reaches 70% after 1000 cycles. More importantly, we have established a direct relationship between the electrochemical kinetics and nanostructure of NGC electrode materials.

Significant Corrosion Resistance in an Ultrafine-Grained Al6063 Alloy with a Bimodal Grain-Size Distribution through a Self-Anodic Protection Mechanism

The bimodal microstructures of Al6063 consisting of 15, 30, and 45 vol. % coarse-grained (CG) bands within the ultrafine-grained (UFG) matrix were synthesized via blending of high-energy mechanically milled powders with unmilled powders followed by hot powder extrusion. The corrosion behavior of the bimodal specimens was assessed by means of polarization, steady-state cyclic polarization and impedance tests, whereas their microstructural features and corrosion products were examined using optical microscopy (OM), scanning transmission electron microscopy (STEM), field emission scanning electron microscopy (FE-SEM), electron backscattered diffraction (EBSD), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) techniques. The bimodal Al6063 containing 15 vol. % CG phase exhibits the highest corrosion resistance among the bimodal microstructures and even superior electrochemical behavior compared with the plain UFG and CG materials in the 3.5% NaCl solution. The enhanced corrosion resistance is attributed to the optimum cathode to anode surface area ratio that gives rise to the formation of an effective galvanic couple between CG areas and the UFG matrix. The operational galvanic coupling leads to the domination of a “self-anodic protection system” on bimodal microstructure and consequently forms a uniform thick protective passive layer over it. In contrast, the 45 vol. % CG bimodal specimen shows the least corrosion resistance due to the catastrophic galvanic corrosion in UFG regions. The observed results for UFG Al6063 suggest that metallurgical tailoring of the grain structure in terms of bimodal microstructures leads to simultaneous enhancement in the electrochemical behavior and mechanical properties of passivable alloys that are usually inversely correlated. The mechanism of self-anodic protection for passivable metals with bimodal microstructures is discussed here for the first time.

Superior performance of highly flexible solid-state supercapacitor based on the ternary composites of graphene oxide supported poly(3,4-ethylenedioxythiophene)-carbon nanotubes

Ternary composite electrodes based on carbon nanotubes thin films (CNFs)-loaded graphene oxide (GO) supported poly(3,4-ethylenedioxythiophene)- carbon nanotubes (GO/PEDOT-CNTs) have been prepared via a facile one-step electrochemical codeposition method. The effect of long and short CNTs-incorporated composites (GO/PEDOT-lCNTs and GO/PEDOT-sCNTs) on the electrochemical behaviors of the electrodes is investigated and compared. Electrochemical measurements indicate that the incorporation of CNTs effectively improves the electrochemical performances of the GO/PEDOT electrodes. Long CNTs-incorporated GO/PEDOT-lCNTs electrodes have more superior electrochemical behaviors with respect to the short CNTs-incorporated GO/PEDOT-lCNTs electrodes, which can be attributed to the optimized composition and specific microstructures of the former. To verify the feasibility of the prepared composite electrodes for utilization as flexible supercapacitor, a solid-state supercapacitor using the CNFs-loaded GO/PEDOT-lCNTs electrodes is fabricated and tested. The device shows lightweight, ultrathin, and highly flexible features, which also has a high areal and volumetric specific capacitance (33.4 m F cm−2 at 10 mV s−1 and 2.7 F cm−3 at 0.042 A cm−3), superior rate capability, and excellent cycle stability (maintaining 97.5% for 5000 cycles). This highly flexible solid-state supercapacitor has great potential for applications in flexible electronics, roll-up display, and wearable devices.

Synthesis of shell-in-shell LiNi0.5Mn1.5O4 hollow microspheres and their enhanced performance for lithium ion batteries

Shell-in-shell LiNi0.5Mn1.5O4 hollow microspheres (SS-LNMO) were synthesized by a facile molten salt and temperature programmed calcination route. SS-LNMO with an average size of 1.2µm and a shell thicknesses of ~120nm were employed as cathode materials for lithium ion batteries. Experiment results showed that SS-LNMO exhibited a good rate performance. At 2C, the reversible capacity after 100 cycles was 140 mAhg−1 with a coulombic efficiency of 97.7%. The superior electrochemical behavior of SS-LNMO could be ascribed to the unique micro-nano assembly hollow structure, simultaneously offering short diffusion distance, cushioning the volume change and maintaining the electrode integrity.

Sustainable carbon-sheets and their MnO–C hybrid for Li-ion batteries

Sustainable carbon have been achieved by a simple treatment of sugarcane-stalk, which exhibits superior electrochemical behavior to graphite. Moreover, the performance can be further upgraded by growing MnO to form a synergetic MnO–C hybrid.

Interpenetrating Framework with Three-Dimensionally Ordered Macroporous Carbon Substrates and Well-Dispersed Co3O4 Nanocrystals for Supercapacitor

In this work, we present the synthesis and electrochemical performance of a novel Co3O4/carbon nanocomposite composed of a homogeneous dispersion of Co3O4 nanocrystals and carbon in a three dimensionally ordered macroporous framework with a pore-hierarchical structure (3DOM Co3O4-C). Structural and morphological properties of the 3DOM Co3O4-C are characterized by various techniques. Cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy tests are employed to assess the properties of the nanocomposite for use in supercapacitor. The results demonstrate that Co3O4 can be effectively utilized with assistance of the carbon in the 3DOM framework. The specific capacitance of the 3DOM Co3O4-C can reach as high as 687.5 F g−1 and 555.2 F g−1 at 20 mV s−1 and 1 A g−1, respectively, much higher than those of the carbon and Co3O4-free 3DOM counterparts. Moreover, the nanocomposite exhibits excellent rate-capability and durable cyclability, keeping over 96% of its initial charge after 5000 cycles at a current density of 10 A g−1. Such superior electrochemical behavior can be attributed to the positive synergetic contributions of Co3O4 and carbon including a short diffusion length for both electrons and OH− ions, large accessible surface area, homogeneously dispersed Co3O4, and the enhanced electrolyte flux.

Large capacitive enhancement of N-doped nanoporous carbon by the addition of novel redox additive of diphenylcarbazide

Nitrogen-doped nanoporous carbon materials have been prepared by a template carbonization method, in which diphenylcarbazide serves as carbon/nitrogen source and Mg(NO3)2·6H2O powder as hard template, respectively. The mass ratio of diphenylcarbazide and Mg(NO3)2·6H2O powder plays a crucial role in determining the pore structures and electrochemical performances. The resulting carbon-2:1 sample displays large BET surface area of 1366m2g−1, and high pore volume of 2.18cm3g−1. It also exhibits good cycling stability and superior electrochemical behaviors, including high specific capacitance of 323.5Fg−1 at 1mAcm−2 in a three-electrode system using 6molL−1 KOH as electrolyte. More importantly, to further improve the electrochemical performance, different amounts (8, 16 and 24mg) diphenylcarbazide herein serving as novel redox additive is introduced into the carbon-2:1 system to form the carbon-2:1-8/16/24 electrodes. As a result, the specific capacitances of the carbon-2:1-8/16/24 electrodes at 2mAcm−2 have been improved up to be 232.7, 344.4 and 497.8Fg−1, respectively, which are 1.02, 1.51, and 2.18 times than that of the pristine system (∼228.8Fg−1). Furthermore, the carbon-2:1-24 also retains high cycling stability as 77.5% after 5000 cycles. The present method of incorporating diphenylcarbazide (redox additive) into carbon system is simple but efficient for large improvement of supercapacitor performances.

Solvent influence on the morphology and supercapacitor performance of the nickel oxide

NiO with different morphologies were fabricated via hydrothermal method in different kinds of solvent. The morphology of the obtained NiO samples varied from nanoflakes to nanoparticles with the different volume ratios of water to ethanol. The electrochemical results showed that the specific capacitance of NiO-S5 obtained in ethanol was up to 1337.5Fg−1 at a current density of 0.62Ag−1, which was greatly higher than that of the other samples. These results indicated that NiO-S5 had the superior electrochemical behavior which may be due to its small-size effect.

3D nanoarchitectures of α-LiFeO2 and α-LiFeO2/C nanofibers for high power lithium-ion batteries

Hydrodynamic structuring of alkoxide-based sols in an electrical field is a promising technique to fabricate one-dimensional materials as free-standing fiber mats with high surface area and precisely controlled microstructure. Hollow α-LiFeO2 and composite α-LiFeO2/C nanofibers were prepared as self-supported 3D architectures of ceramic fibers by single-step electrospinning of metal alkoxide sols. The spinel fibers exhibited a crystalline spinel phase with uniform fiber diameter and morphology that was modified by a thin sheath of amorphous carbon in the composite fibers that enhances the electrical conductivity and also has a structure-holding influence. The atomic scale mixing and pre-existing LiOFe units in the spinning solution were the delivers of observed phase purity and control over the surface properties verified by high resolution TEM data. Galvanostatic and potentiostatic studies confirmed the superior electrochemical behaviors of α-LiFeO2 and α-LiFeO2/C nanofibers as high-energy density anode materials in half-cell configuration. α-LiFeO2/C composite nanofibers showed after 50 cycles a discharge capacity of 821mAh/g at 0.1C with a capacity retention of 75% from the 2nd to 50th cycle, whereas the discharge capacity of α-LiFeO2-hollow nanofibers was found to be 756mAh/g with a capacity retention of 68%. Flexible composite nanofiber networks are promising solution enabling improved electronic and ionic conductivity and mechanical stability for the development of lithium-ion batteries with high power and energy densities. Investigations on the stability and rate capability of α-LiFeO2/C-composite electrode studied at different rates of 0.1C, 0.25C and 0.5C for 75 cycles also showed high capacity values that indicated their potential as anode materials.

A generalized ZnCl2 activation method to produce nitrogen-containing nanoporous carbon materials for supercapacitor applications

We demonstrate a generalized but efficient ZnCl2 activation method to produce nitrogen-containing nanoporous carbon materials, using 4-(4-nitrophenylazo)resorcinol, sodium 5-[(4-nitrophenyl)azo]salicylate, and tartrazine as carbon/nitrogen sources. It reveals that the mass ratios between carbon/nitrogen precursors and ZnCl2 activating agent, and activation temperatures have crucial impacts upon carbon structures as well as the resultant capacitive behaviors. The carbon samples produced in this work are amorphous in nature. The carbon sample obtained by the ZnCl2 activation of 4-(4-nitrophenylazo)resorcinol at 900°C, named as carbon-1#, exhibits the largest nitrogen contents of 5.96% and best porosity, including the BET surface area of 891.1m2g−1, and total pore volume of 0.54cm3g−1. As a result, the carbon-1# sample delivers the superior specific capacitances of 431.5Fg−1 at a current density of 1Ag−1, as well as long-term cycling stability of 97.16% even after charging-discharging for 10,000 times. The present ZnCl2 activation method is expected to produce other carbon materials, exhibiting large porosities and superior electrochemical behaviors for supercapacitor applications.

Self-stacked nitrogen-doped carbon nanotubes as long-life air electrode for sodium-air batteries: Elucidating the evolution of discharge product morphology

Self-stacked nitrogen-doped carbon nanotubes (NCNTs) and pristine carbon nanotubes (CNTs) on commercial porous polypropylene substrates have been applied as air electrodes for sodium-air batteries (SAB). Both NCNT and CNT air electrodes exhibit highly reversible electrochemical activities and large capacities under low current densities in SABs, while NCNT electrodes show much higher rate performance and extended cycling life under high current densities. The superior electrochemical behavior of NCNT electrodes is attributed to the robust network of aligned NCNTs, which enables rapid oxygen and liquid electrolyte transport while accommodating the volume change originating from discharge product aggregation during cycling. Moreover, uniform coverage of the discharge product has been observed on the NCNT air electrodes, in contrast to the random and discrete dispersion of discharge product on the CNT air electrodes. The unique morphologies and growth mechanism of discharge products on NCNT electrodes are believed to be due to the outstanding catalytic activity of the nitrogen-doped sites in the NCNTs, which play a critical role in the high cycling stability of NCNT air electrodes for SABs.

Promising gaseous and electrochemical hydrogen storage properties of porous Mg-Pd films under mild conditions.

In this paper, the gaseous and electrochemical hydrogen storage properties of 200 nm Mg-Pd thin films with different morphologies have been investigated. The results show that Mg-Pd films become porous with the increase of substrate temperature. Porous Mg-Pd films exhibit superior gaseous and electrochemical hydrogen storage behaviors under mild conditions, including rapid hydrogen sorption kinetics, a large hydrogen storage amount, high electrochemical discharge capacity, and a fast hydrogen diffusion rate. The excellent behaviors of porous Mg-Pd films might be ascribed to the significantly shortened hydrogen diffusion paths and the large contact areas between the hydrogen gas and the solid Mg phases, which are elucidative for the development and applications of thick Mg-Pd films.

Nitrogen-containing nanoporous carbons with high pore volumes from 4-(4-nitrophenylazo)resorcinol by a Mg(OH)2-assisted template carbonization method

Producing nanoporous carbons that possess high porosity and superior electrochemical performance is a challenge for scientists. In this work, a simple and efficient template carbonization method, without any physical/chemical activation treatment, has been implemented to produce nanoporous carbons doped with nitrogen species. 4-(4-Nitrophenylazo)resorcinol serves as a carbon/nitrogen source and Mg(OH)2 as a hard template. All resultant carbon samples are amorphous, highly porous in nature and display sheet-like nanostructures. The carbon-1:3-L sample whose precursor is obtained by solution method exhibits better porosity, and larger nitrogen content, than those obtained by solid state method (the carbon-1:3-S sample). The carbon-1:3-L sample exhibits large specific surface area (SBET) of 1427.7 m2 g−1, and high total pore volume (VT) of 5.91 cm3 g−1, whereas those of the carbon-1:3-S sample are of 1036.6 m2 g−1 and 4.76 cm3 g−1, respectively. Notably, the present pore volumes are much higher than most of the previously reported for nanoporous carbons. As a consequence, the carbon-1:3-L sample delivers superior electrochemical behaviors, whose specific capacitance reaches up to 378.5 F g−1 when measured at 1 A g−1 in a three-electrode system, compared with that of 263.4 F g−1 of the carbon-1:3-S sample. The present Mg(OH)2-assisted template carbonization method is simple and easy to operate, indicating its potential application for producing nanoporous carbons.

Structure and electrochemical performance of nitrogen-containing nanoporous carbon from diphenylcarbazide via a template carbonization route

In this work, a simple template carbonization method has been developed to produce nitrogen-containing nanoporous carbon from diphenylcarbazide, using Mg(OH)2 as hard template. The carbonization temperature has a crucial role in determining the carbon structure. The carbon-3:1-800 sample obtained with the mass ratio of diphenylcarbazide and Mg(OH)2 as 3:1 at 800°C exhibits the optimum pore structure as well as the resultant best electrochemical performance. It has a large BET surface area of 1538.0 m2g−1, high pore volume of 3.48 cm3g−1, and hierarchical pore size distribution. As a result, it delivers superior electrochemical behaviors in a three-electrode system using 6molL−1 KOH as electrolyte, whose specific capacitance calculated from galvanostatic charge-discharge curve can reach up to 517.4 F g−1 at a current density of 1 A g−1, which is much larger than most of the nanocarbons ever reported in the literature. The carbon-3:1-800 sample also exhibits good cycling stability within 10000 cycles. Comparatively, the electrochemical test has also been carried out in a two-electrode system using [EMIm]BF4/AN as electrolyte. More importantly, the operation temperatures of 25/50/80°C can greatly broaden the application scope of nanoporous carbon in the supercapacitor.

High performance supercapacitor electrode material based on vertically aligned PANI grown on reduced graphene oxide/Ni(OH)2 hybrid composite

Unique vertically aligned PANI on rGO/Ni(OH)2 composite has been synthesized by a hydrothermal method exhibiting superior electrochemical behavior.

Curly Graphene with Specious Interlayers Displaying Superior Capacity for Hydrogen Storage

While almost all attempts for bulk synthesis of graphene result in agglomeration of flat graphene layers, a simple solvothermal route is reported for the preparation of a graphene powder consisting of very flexible sheets. Curvature of these graphene sheets avoids vital agglomeration, which normally blocks the accessible surface of graphene sheets. The thickness of the graphene sample varies from one to a few layers, but the spaces among the graphene layers are sufficiently large enough to provide internal accessibility. Thus, this graphene sample shows the general (bulk) properties of graphene single sheets. For instance, it has a high specific surface area of ca. 1168 m2 g–1 and starts to burn at 350 °C because of a large interlayer spacing of graphene sheets (i.e., 5.1 Å). It should be considered that this specious interlayer is mostly due to the graphene curvature rather than to filling with functional groups (as in the case of graphite oxide). Owing to the high accessibility and active sites over a large surface area, this graphene sample shows a superior electrochemical behavior for hydrogen storage.

Crumpled Graphene–Molybdenum Oxide Composite Powders: Preparation and Application in Lithium‐Ion Batteries

Crumpled graphene-MoO2 composite powders are directly prepared by means of spray pyrolysis and from a stable graphene oxide colloidal solution in the presence of Mo ions. The crumpled graphene-MoO2 composite powders are transformed into MoO3 -based composite powders after post-treatment at 300 °C. The transmission electron microscopy and dot-mapping images of the post-treatment composite powders show uniform distribution of MoO3 nanocrystals in the crumpled graphene powders. The two typical D and G bands of graphene are observed at 1350 and 1590 cm(-1) , respectively, in the Raman spectrum of the graphene-MoO3 composite. In addition, the crumpled graphene-MoO3 powders exhibit superior electrochemical behavior compared to that of pure MoO3 as an anode material for lithium-ion batteries. The initial discharge capacities of the graphene-MoO3 composite and bare MoO3 powders at a current density of 2 A g(-1) are 1490 and 1225 mA h g(-1) , respectively. The capacity retention of the graphene-MoO3 composite is 87 % after the first cycle, whereas that of bare MoO3 is 47 %, as measured after 100 cycles. The reversible discharge capacity of the graphene-MoO3 composite decreases slightly from 1228 to 845 mA h g(-1) as the current density increases from 0.5 to 3 A g(-1) .

Hydrothermal synthesis of α-Ni(OH)2 and its conversion to NiO with electrochemical properties

Abstract The paper reports the fabrication of microscale NiO matrixes with enhanced electrochemical properties through annealing the corresponding chrysanthemum-like α-Ni(OH)2 microspheres. The precursor α-Ni(OH)2 can be synthesized by a hydrothermal method using triethanolamine as the alkaline source. The formation mechanism of chrysanthemum-like α-Ni(OH)2 microspheres is properly discussed. Furthermore, the electrochemical experiments demonstrate that the microscale NiO matrixes show superior electrochemical behavior in lithium-ion batteries due to their unique structures.

Graphene oxide/nickel oxide modified glassy carbon electrode for supercapacitor and nonenzymatic glucose sensor

Based on the extraordinarily properties of graphene oxide (GO), nickel oxide nanoparticles (NiONPs)/GO/glassy carbon (GC) modified electrode was prepared by electrodeposition of NiONPs on the GC surface previously modified with GO, which was characterized by scanning electron microscope (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The results showed that GO was partially reduced and three-dimensional NiONPs were electrochemically synthesized on the surface of GO. Compared with NiONPs/GC electrode, NiONPs/GO/GC modified electrode exhibited more excellent conductivity, more superior electrochemical capacitive behavior (16-folds) and better electro-catalytic oxidation of glucose, applying for the electrochemical detection of glucose. The linear range for glucose is from 3.13μM to 3.05mM with the detection limit of 1μM. In addition, the effects of common interfering species, including ascorbic acid (AA), uric acid (UA), and NaCl were investigated in detail. The result indicated that these foreign substances did not interfere significantly on the determination of glucose.