Electrochemical performance of CeO<Subscript>2</Subscript> nanoparticle-decorated graphene oxide as an electrode material for supercapacitor

Cerium oxide nanoparticles and cerium oxide nanoparticle-decorated graphene oxide (GO) are synthesized via a facile chemical coprecipitation method in the presence of hexadecyltrimethylammonium bromide (CTAB). Nanostructure studies and electrochemical performances of the as-prepared samples were systematically investigated. The crystalline structure and morphology of the nanocomposites were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transition electron microscopy (TEM), Raman spectrum, and X-ray photoelectron spectroscopy (XPS). Electrochemical properties of the CeO₂ electrode, the GO electrode, and the nanocomposites electrodes were investigated by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) measurements. The CeO₂ nanoparticle-decorated GO (at the mole ratio of CeO₂/GO = 1:4) electrode exhibited excellent supercapacitive behavior with a high specific capacitance of 382.94 F/g at the current density of 3.0 A/g. These superior electrochemical features demonstrate that the CeO₂ nanoparticle-decorated GO is a promising material for next-generation supercapacitor systems.     

Hydrothermal synthesis of pure LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> from nanostructured MnO<Subscript>2</Subscript> precursors for aqueous hybrid supercapacitors

Pure LiMn₂O₄ samples with high crystallinity (LMO-1# and LMO-2#) were successfully synthesized by a facile hydrothermal method using δ-MnO₂ nanoflowers and α-MnO₂ nanowires as the precursors. The as-prepared samples were analyzed by XRD, SEM, and Brunauer-Emmett-Teller (BET), and their capacitive properties were investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge test. Two LiMn₂O₄ samples showed good capacitive behavior in aqueous hybrid supercapacitors. AC//LMO-1# and AC//LMO-2# delivered the initial specific capacitance of 45.4 and 40.7 F g^?1 in 1 M Li₂SO₄ electrolyte at a current density of 200 mA g^?1 in the potential range of 0～1.5 V, respectively. After 1000 cycles, the capacitance retention was 97.6% for AC//LMO-1# and 93.7% for AC//LMO-2#. Obviously, LMO-1# from δ-MnO₂ nanoflowers exhibited higher specific capacitance and better cycling performance than LMO-2#, so LMO-1# was more suitable as the positive electrode material in hybrid supercapacitors.     

Synthesis of hierarchical nanospheres Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/graphene composite and its application in lithium-ion battery as a high-performance anode material

A hierarchically nanospherical α-Fe₂O₃/graphene composite with a homogeneous mono-pore size of 4 nm has been prepared using a hydrothermal method. The composite showed an extremely high rate performance and good cycling stability when applied as an anode material for lithium-ion batteries owing to its unique three dimensional architecture. A specific capacity of 110 mAh/g was obtained at an extremely high current rate of 40 A/g and recover to 830 mAh/g at 0.5 A/g after 60 cycles. After 250 cycles at 2 A/g, the composite electrode exhibited a capacity of 630 mAh/g with a columbic efficiency of 99.5 %.     

Hierarchical porous ZnMn<Subscript>2</Subscript>O<Subscript>4</Subscript> synthesized by the sucrose-assisted combustion method for high-rate supercapacitors

A simple sucrose-assisted combustion and subsequent high-temperature calcination route have been employed to prepare hierarchical porous ZnMn₂O₄ nanostructure. When used as an electrode for supercapacitor, the ZnMn₂O₄ electrode displays a high specific capacitance of 411.75 F g^?1 at a current density of 1 A g^?1, remarkable capacitance retention rate of 64.28 % at current density of 32 A g^?1 compared with 1 A g^?1, as well as excellent cycle stability (reversible capacity retention of 88.32 % after 4000 cycles). The outstanding electrochemical performances are mainly attributed to its hierarchical porous architecture, which provides large reaction surface area, fast ion and electron transfer, and good structure stability. All these impressive results demonstrate that ZnMn₂O₄ shows promise for its application in supercapacitors.     

Spray pyrolysis-deposited TiO<Subscript>2</Subscript> thin films as high-performance lithium ion battery anodes

Focusing on additive-free electrodes, thin films are of typical interest as electrodes for lithium ion battery application. Herein, we report the fabrication of TiO₂ thin films by spray pyrolysis deposition technique. X-ray diffraction and transmission electron microscopic analysis confirms the formation of anatase TiO₂. Electrochemical evaluation of these sub-micron TiO₂ thin films exhibits high-rate performance and long cycling stability. At 1C rate (1C?=?335 mA/g), the electrode delivered discharge capacity of 247 mAh/g allowing about 0.74 lithium into the structure. The electrodes also delivered specific capacities of 122 and 72 mAh/g at 10 and 30C rates, respectively. Without conductive additives, this excellent performance can be attributed to the nanosize effect of TiO₂ particles combined with the uniform porous architecture of the electrode. Upon cycling at high rates (10 and 30C), the electrode exhibited excellent cycling stability and retention, specifically only <?0.6% capacity loss per cycle over 2500 cycles.     

Nanocrystalline Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> electrodes for supercapattery application

Nanocrystalline Li₂TiO₃ was successfully synthesized using solid-state reaction method. The microstructural and electrochemical properties of the prepared material are systematically characterized. The X-ray diffraction pattern of the prepared material exhibits predominant (002) orientation related to the monoclinic structure with C2/c space group. HRTEM images and SAED analysis reveal the well-developed nanostructured particles with average size of ～40 nm. The electrochemical properties of the prepared sample are carried out using cyclic voltammetry (CV) and chronopotentiometry (CP) using Pt//Li₂TiO₃ cell in 1 mol L^?1 Li₂SO₄ aqueous electrolyte. The Li₂TiO₃ electrode exhibits a specific discharge capacity of 122 mAh g^?1; it can be used as anode in Li battery within the potential window 0.0–1.0 V, while investigated as a supercapacitor electrode, it delivers a specific capacitance of 317 F g^?1 at a current density of 1 mA g^?1 within the potential range ?0.4 to +0.4 V. The demonstration of both anodic and supercapacitor behavior concludes that the nanocrystalline Li₂TiO₃ is a suitable electrode material for supercapattery application.     

Hexagonal-like NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript> nanostructure based high-performance supercapacitor electrodes

A novel approach of double hydroxide-mediated synthesis of nickel cobaltite (NiCo₂O₄) electro-active material by the hydrothermal method is reported. The obtained NiCo₂O₄ electro-active material displays the spinel cubic phase and hexagonal-like morphology. Thermogravimetry analysis confirms the thermal stability of the electrode material. The functional groups and phase formation of NiCo₂O₄ have been confirmed by FT-IR and Raman spectral analysis. The modified NiCo₂O₄ electrode exhibits the highest specific capacitance of 767.5 F g^?1 at a current density of 0.5 A g^?1 in 3 M KOH electrolyte and excellent cyclic stability (94 % capacitance retention after 1000 cycles at a high current density of 5 A g^?1). The excellent electrochemical performance of the electrode is attributed to the hexagonal-like morphology, which contributes to the rich surface electro-active sites and easy transport pathway for the ions during the electrochemical reaction. The attractive Faradic behavior of NiCo₂O₄ electrode has been ascribed to the redox contribution of Ni²⁺/Ni³⁺ and Co²⁺/Co³⁺ metal species in the alkaline medium. The symmetrical two-electrode cell has been fabricated using the NiCo₂O₄ electro-active material with excellent electrochemical properties for supercapacitor applications.     

Morphology-controlled PANI nanowire electrode by using deposition scan rate in H<Subscript>2</Subscript>SO<Subscript>4</Subscript>/PVA polymer electrolyte for electrochemical capacitor

Polyaniline (PANI) nanowire electrode was successfully prepared using electrodeposition method. The morphology, thickness, and electrochemical performance of PANI electrode can be controlled by varying the deposition scan rates. Lower deposition scan rate results in compact and aggregates of PANI nanowire morphology. The uniform nanowire of PANI was obtained at the applied scan rate of 100 mV s^?1, and it was used as symmetric electrode coupled with H₂SO₄/polyvinyl alcohol (PVA) gel electrolyte. The different concentrations of H₂SO₄ acid in polymer electrolyte have influenced the electrochemical performance as well. The optimum specific capacitance and energy density of P100 PANI electrode in 3 M H₂SO₄/PVA gel polymer electrolyte was 377 F g^?1 and 95.4 Wh kg^?1 at the scan rate of 1 mV s^?1. The good stability of the electrode in this system is applicable to many wearable electronics applications.     

Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/functional exfoliation graphene on carbon paper nanocomposites for supercapacitor electrode

In this work, the commercial carbon paper was firstly peeled in K₂CO₃ solution and then was further treated in a KNO₃ solution to form functional exfoliation graphene (FEG) on the commercial carbon paper. The FEG/carbon paper was characterized by Raman spectra and scanning electron microscopy, confirming that some typical layered fold graphenes were successfully peeled off and stood on the carbon paper matrix. Then, Fe₃O₄ nanoparticles (NPs) were grown on the surface of FEG/carbon paper and the as-prepared Fe₃O₄ NPs/FEG/carbon paper was directly used as supercapacitor electrode. The specific capacitance of Fe₃O₄ NPs/FEG/carbon paper was about 316.07 F g^?1 at a current density of 1 A g^?1. Furthermore, the FEG/carbon papers were also functionalized by benzene carboxylic acid to form FFEG/carbon papers, and then the Fe₃O₄ NPs were grown on the surface of FFEG/carbon paper. The specific capacitance of Fe₃O₄ NPs/FFEG/carbon paper was 470 F g^?1 at a current density of 1 A g^?1, superior to some previous reported results. This work might provide a new strategy to prepare various nanostructures on FFEG/carbon papers for future applications.     

Novel synthesis and characterization of ZnCo<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoflakes grown on nickel foam as efficient electrode materials for electrochemical supercapacitors

ZnCo₂O₄ nanoflakes were directly grown on Ni foam via a two-step facile strategy, involving cathodic electrolytic electrodeposition (ELD) method and followed by a thermal annealing treatment step. The results of physical characterizations exhibit that the mesoporous ZnCo₂O₄ nanoflakes have large electroactive surface areas (138.8 m² g^?1) and acceptable physical stability with the Ni foam, providing fast electron and ion transport sites. The ZnCo₂O₄ nanoflakes on Ni foam were directly used as integrated electrodes for supercapacitors and their electrochemical properties were measured in 2 M KOH aqueous solution. The ZnCo₂O₄ nanoflake electrode exhibits a high capacitance of 1781.7 F g^?1 at a current density of 5 A g^?1 and good rate capability (62% capacity retention at 50 A g^?1). Also, an excellent cycling ability at various current densities from 5 to 50 A g^?1 was obtained and 92% of the initial capacitance maintained after 4000 cycles. The results demonstrate that the proposed synthesis route is cost-effective and facile and can be developed for preparation of electrode materials in other electrochemical supercapacitors.     

Roles of Al-doped ZnO (AZO) modification layer on improving electrochemical performance of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> thin film cathode

Al-doped ZnO (AZO) was sputtered on the surface of LiNi_1/3Co_1/3Mn_1/3O₂ (NCM) thin film electrode via radio frequency magnetron sputtering, which was demonstrated to be a useful approach to enhance electrochemical performance of thin film electrode. The structure and morphology of the prepared electrodes were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometer, and transmission electron microscopy techniques. The results clearly demonstrated that NCM thin film showed a strong (104) preferred orientation and AZO was uniformly covered on the surface of NCM electrode. After 200 cycles at 50 μA μm^?1 cm^?2, the NCM/AZO-60s electrode delivered highest discharge capacity (78.1 μAh μm^?1 cm^?2) compared with that of the NCM/AZO-120s electrode (62.4 μAh μm^?1 cm^?2) and the bare NCM electrode (22.3 μAh μm^?1 cm^?2). In addition, the rate capability of the NCM/AZO-60s electrode was superior to the NCM/AZO-120s and bare NCM electrodes. The improved electrochemical performance can be ascribed to the appropriate thickness of the AZO coating layer, which not only acted as HF scavenger to keep a stable electrode/electrolyte interface but also reduced the charge transfer resistance during cycling.     

Free-standing WS<Subscript>2</Subscript><Emphasis Type="Strikethrough">-</Emphasis>MWCNTs hybrid paper integrated with polyaniline for high-performance flexible supercapacitor

As two-dimensional layered nanomaterials, the tungsten disulfide (WS₂) nanosheets can be used as building blocks of paper-like electrodes for high-performance FSs. However, poor conductivity and mechanical property of WS₂ nanosheets (NSs) paper greatly hinders their capacitance and/or rate performance. To solve these problems, we fabricated the WS₂-multiwalled carbon nanotubes (MWCNTs)/polyaniline (PANI) composite papers based on liquid exfoliation and electrochemical deposition for high-performance flexible supercapacitors. The WS₂-MWCNTs/PANI with conductive PANI chains linked WS₂ NSs and MWCNTs takes the advantages of high-electronic double-layer capacitance originated from the internal surface areas of MWCNTs and effective pseudocapacitance generated by exfoliated WS₂ NSs and PANI. Electrochemical studies showed that the gravimetric-specific capacitance of WS₂-MWCNTs/PANI can reach ~760.1 F/g at a current density of 1 A/g. A symmetric flexible solid-state supercapacitor was also assembled and studied. The WS₂-MWCNTs/PANI-assembled FS device also has an excellent area specific capacitance of 1158.7 mF/cm² at a current density of 0.5 mA/cm² together with a high-capacity retention of ~82.5% after 2000 cycles.     

Correlation between the mesoporous carbon sphere with Ni(OH)<Subscript>2</Subscript> nanoparticle contents for high-performance supercapacitor electrode

Ni(OH)₂ nanoparticles were decorated on mesoporous carbon spheres (MPCS) using a simple hard template method. The MPCS were derived from sodium carboxymethyl cellulose. As-prepared MPCS/Ni(OH)₂ nanocomposites were used as electrode materials for supercapacitors. These composites exhibited better electrochemical properties than a pristine mesoporous carbon sphere owing to the synergistic effect. However, the increase in Ni(OH)₂ is not proportional to the electrochemical performance improvement. The addition of an optimal amount of Ni(OH)₂, typically 1:20 by weight (MPCS:NiCl₂·6H₂O), showed an excellent specific capacitance of 1338.296 F g^?1 at a scan rate of 5 mV s^?1. These encouraging results indicate excellent potential for the development of highly capacitive energy storage devices for practical applications.     

A novel synthesis of size-controllable mesoporous NiMoO<Subscript>4</Subscript> nanospheres for supercapacitor applications

A novel hydrothermal emulsion method is proposed to synthesize mesoporous NiMoO₄ nanosphere electrode material. The size of sphere-shaped NiMoO₄ nanostructure is controlled by the mass ratio of water and oil phases. Nickel acetate tetrahydrate and ammonium heptamolybdate were used as nickel and molybdate precursors, respectively. The resultant mesoporous NiMoO₄ nanospheres were characterized by X-ray diffraction, N₂ adsorption and desorption, scanning electron microscopy, and transmission electron microscopy. The electrochemical performances were evaluated by cyclic voltammetry (CV), cyclic chronopotentiometry (CP), and electrochemical impedance spectroscopy (EIS) in 6 M KOH solution. The typical mesoporous NiMoO₄ nanospheres exhibit the large specific surface area of 113 m² g^?1 and high specific capacitance of 1443 F g^?1 at 1 A g^?1, an outstanding cyclic stability with a capacitance retention of 90 % after 3000 cycles of charge-discharge at a current density of 10 A g^?1, and a low resistance.     

Fabrication and electrochemical performance of La<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>CoO<Subscript>3</Subscript> impregnated porous YSZ cathode

La_0.5Sr_0.5CoO₃-yttria-stabilized zirconia (LSCO-YSZ) composite cathode for solid oxide fuel cell (SOFC) has been fabricated by wet impregnation method. Nitrate precursors of La, Sr, and Co have been impregnated into the pre-sintered porous YSZ matrix, which is converted into LSCO phase after calcination at 850 °C in the presence of glycine as confirmed from X-ray diffraction. LSCO of 5, 7, and 10 wt% impregnated porous YSZ have been electrochemically characterized using 2-probe AC conductivity method. Maximum ionic conductivity of 0.27 S/cm at 800 °C and activation energy of 0.15 eV between 600 and 800 °C have been observed for 10 wt% LSCO-YSZ cathode. Area-specific resistance of 1.01 Ω cm² at 800 °C is estimated for the electrolyte-supported half-cell (10 wt% LSCO-YSZ/YSZ). After testing the LSCO-YSZ cathode matrix, the electrolyte-supported full cell (10 wt% LSCO-YSZ/YSZ/NiO-YSZ) has been tested and produced maximum power density 51.12 mW/cm² (109.38 mA/cm²) at 800 °C. The electrolyte-supported full cell exhibited 6 Ω cm² electrode polarization at 800 °C in H₂, which is in higher side leading to low performance. LSCO-YSZ/YSZ/NiO-YSZ SOFC found to give stable performance up to 2 h and scanning electron microscopy analysis has been carried out before and after cell testing to assess the morphological changes.     

Vertical aligned V<Subscript>2</Subscript>O<Subscript>5</Subscript> nanoneedle arrays grown on Ti substrate as binder-free cathode for lithium-ion batteries

V₂O₅ nanoneedle arrays were grown directly on titanium (Ti) substrate by a facile solvothermal route followed with calcination at 350 °C for 2 h. The as-prepared V₂O₅ nanoneedles are about 50 nm in diameter and 800 nm in length. The electrochemical behavior of V₂O₅ nanoarrays as binder-free cathode for lithium-ion batteries (LIBs) was evaluated by cyclic voltammetry and galvanostatic discharge/charge tests. Compared with V₂O₅ powder electrode, V₂O₅ nanoneedle arrays electrode exhibited improved electrochemical performance in terms of high discharge capacity of 262.5 mA h g^?1 between 2.0 and 4.0 V at 0.2 C, and high capacity retention up to 77.1% after 100 cycles. Under a high current rate of 2 C, a discharge capacity of about 175.6 mA h g^?1 can be maintained. The enhanced performance are mainly due to the intimate contact between V₂O₅ nanoneedle active material and current collector, which enable shortened electron transfer pathway and improved charge transfer kinetics, demonstrating their potential applications in high rate electrochemical storage devices.     

Dandelion-like mesoporous Co<Subscript>3</Subscript>O<Subscript>4</Subscript> as anode materials for lithium ion batteries

A dandelion-like mesoporous Co₃O₄ was fabricated and employed as anode materials of lithium ion batteries (LIBs). The architecture and electrochemical performance of dandelion-like mesoporous Co₃O₄ were investigated through structure characterization and galvanostatic charge/discharge test. The as-prepared dandelion-like mesoporous Co₃O₄ consisted of well-distributed nanoneedles (about 40 nm in width and about 5 μm in length) with rich micropores. Electrochemical experiments illustrated that the as-prepared dandelion-like mesoporous Co₃O₄ as anode materials of LIBs exhibited high reversible specific capacity of 1430.0 mA h g^?1 and 1013.4 mA h g^?1 at the current density of 0.2 A g^?1 for the first and 100th cycle, respectively. The outstanding lithium storage properties of the as-prepared dandelion-like mesoporous Co₃O₄ might be attributed to its dandelion-like mesoporous nanostructure together with an open space between adjacent nanoneedle networks promoting the intercalation/deintercalation of lithium ions and the charge transfer on the electrode. The enhanced capacity as well as its high-rate capability made the as-prepared dandelion-like mesoporous Co₃O₄ to be a good candidate as a high-performance anode material for LIBs.     

Carbon@SnS<Subscript>2</Subscript> core-shell microspheres for lithium-ion battery anode materials

A novel unique C@SnS₂ core-shell structure composites consisting of well-dispersity carbon microspheres and ultrathin tin disulfide nanosheets were successfully synthesized for the first time through a simple solvothermal method. The thin SnS₂ nanosheets grew onto the carbon microspheres surfaces perpendicularly and formed the close-knit porous structure. When it was used as anode materials for lithium-ion batteries, the hybrid C@SnS₂ core-shell structure composites showed a remarkable electrochemical property than pure SnS₂ nanosheets. Typically, the hybrid composites with SnS₂ nanosheet shells and carbon microsphere’s core exhibited an excellent initial discharge capacity of 1611.6 mAh/g. Moreover, the hybrid composites exhibited capacities of 474.8–691.6 mAh/g at 100 mA/g over 50 battery cycles, while the pure SnS₂ could deliver capacities of 243–517.6 mAh/g in the tests. The results indicated that the improvement of lithium storage performance of the core-shell structure C@SnS₂ anode materials in terms of rate capability and cycling reversibility owing to the introduction of the smooth carbon microspheres and special designing of core-shell structure.     

Cauliflower-derived porous carbon without activation for electrochemical capacitor and CO<Subscript>2</Subscript> capture applications

Carbon materials have attracted great attention in CO₂ capture and energy storage due to their excellent characteristics such as tunable pore structure, modulated surface properties and superior bulk conductivities, etc. Biomass, provided by nature with non-toxic, widespread, abundant, and sustainable advantages, is considered to be a very promising precursor of carbons for the view of economic, environmental, and societal issues. However, the preparation of high-performance biomass-derived carbons is still a big challenge because of the multistep process for their synthesis and subsequent activation. Herein, hierarchically porous structured carbon materials have been prepared by directly carbonizing dried cauliflowers without any addition of agents and activation process, featuring with large specific surface area, hierarchically porous structure and improved pore volume, as well as suitable nitrogen content. Being used as a solid-state CO₂ adsorbent, the obtained product exhibited a high CO₂ adsorption capacity of 3.1 mmol g^?1 under 1 bar and 25 °C and a remarkable reusability of 96.7% retention after 20 adsorption/regeneration cycles. Our study reveals that choosing a good biomass source was significant as the unique structure of precursor endows the carbonized product with abundant pores without the need of any post-treatment. Used as an electrode material in electrochemical capacitor, the non-activated porous carbon displayed a fairly high specific capacitance of 228.9 F g^?1 at 0.5 A g^?1 and an outstanding stability of 99.2% retention after 5000 cycles at 5 A g^?1.

Open image in new window

Graphical abstract Hierarchically porous structured carbon materials are prepared by directly carbonizing dried cauliflower without any agents and process of activation for high performance of CO₂ capture and capacitor.

     

A facile synthesis about amorphous CoS<Subscript>2</Subscript> combined with first principle analysis for supercapacitor materials

The structure and electrochemical properties of amorphous CoS₂ and crystalline CoS₂ have been studied with both experimental characterization and theoretical calculations. In the field of experimental characterization, a facile chemical precipitation method is used to synthesize amorphous and crystalline CoS₂ samples with calcining temperatures of 200 and 280 °C, respectively. Comparing with crystalline CoS₂, amorphous structure of CoS₂ manifests great electron conductivity, effective porous structure, and exhibit a high specific capacitance of 996.16 F g^?1 at current density of 0.5 A g^?1, excellent rate capability of 89.8% retention with the current density ranging from 0.5 to 5 A g^?1, and a great cycling stability of 97.6% retention after 10,000 cycles at 2 A g^?1 in 6 mol L^?1 KOH aqueous electrolyte. In the area of theoretical calculation, we used the first principle and obtained the band structure with band gap of 0.00369 eV and DOSs with high locality of D-orbital from 69.88689 electrons/eV main peak, in the CoS₂ amorphous. The result confirms that amorphous CoS₂ have higher conductivity than crystalline CoS₂ in theory. In addition, the as-assembled asymmetric supercapacitor of Co-S-200//AC also exhibits the maximum specific capacitance of 104 F g^?1 within a cell voltage from 0 to 1.5 V at current density of 0.5 A g^?1 and indicates a great cycling stability of 95.68% and excellent capacitance behavior. All results demonstrate a great potential of amorphous CoS₂ active material for supercapacitors.