Hydrothermally synthesized Co3O4 microspheres were anchored to graphite oxide (GO) and thermally reduced graphene oxide (rGO) composites at different cobalt weight percentages (1, 10, and 100 wt%). The composite materials served as the active materials in bulk electrodes for two-electrode cell electrochemical capacitors (ECCs). GO/Co3O4–1 exhibited a high energy density of 35 W kg?1 with a specific capacitance (Csp) of 196 F g?1 at a maximum charge density of 1 A g?1. rGO/Co3O4-100 presented high specific power output values of up to 23.41 kW h kg?1 with linear energy density behavior for the charge densities applied between 0.03 and 1 A g?1. The composite materials showed Coulombic efficiencies of 96 and 93 % for GO/Co3O4–1 and rGO/Co3O4–100 respectively. The enhancement of capacitive performance is attributed to the oxygenated groups in the GO ECC and the specific area in the rGO ECC. These results offer an interesting insight into the type of carbonaceous support used for graphene derivative electrode materials in ECCs together with Co3O4 loading to improve capacitance performance in terms of specific energy density and specific power.
A porous, hollow, microspherical composite of Li2MnO3 and LiMn1/3Co1/3Ni1/3O2 (composition: Li1.2Mn0.53Ni0.13Co0.13O2) was prepared using hollow MnO2 as the sacrificial template. The resulting composite was found to be mesoporous; its pores were about 20 nm in diameter. It also delivered a reversible discharge capacity value of 220 mAh g?1 at a specific current of 25 mA g?1 with excellent cycling stability and a high rate capability. A discharge capacity of 100 mAh g?1 was obtained for this composite at a specific current of 1000 mA g?1. The high rate capability of this hollow microspherical composite can be attributed to its porous nature.
The three-dimensional porous Li3V2(PO4)3/nitrogen-doped reduced graphene oxide (LVP/N-RGO) composite was prepared by a facile one-pot hydrothermal method and evaluated as cathode material for lithium-ion batteries. It is clearly seen that the novel porous structure of the as-prepared LVP/N-RGO significantly facilitates electron transfer and lithium-ion diffusion, as well as markedly restrains the agglomeration of Li3V2(PO4)3 (LVP) nanoparticles. The introduction of N atom also has positive influence on the conductivity of RGO, which improves the kinetics of electrochemical reaction during the charge and discharge cycles. It can be found that the resultant LVP/N-RGO composite exhibits superior rate properties (92 mA h g?1 at 30 C) and outstanding cycle performance (122 mA h g?1 after 300 cycles at 5 C), indicating that nitrogen-doped RGO could be used to improve the electrochemical properties of LVP cathodes for high-power lithium-ion battery application.
Graphical abstract The three-dimensional porous Li3V2(PO4)3/nitrogen-doped reduced graphene oxide composite with significantly accelerating electron transfer and lithium-ion diffusion exhibits superior rate property and outstanding cycle performance.
In this work, Bi3.64Mo0.36O6.55 nanoparticles (NPs) were successfully prepared by a facile hydrothermal method and utilized in pseudocapacitor for the first time. Within a redox potential range from ?1.0 to 0 V vs. Hg/HgO in a 1 M aqueous KOH solution by cyclic voltammetry (CV), chronopotentiometry (CP) and AC impendence, the specific capacitance could reach 998 F g?1 at 1 A g?1, which is possibly ascribed to the higher Bi content of Bi3.64Mo0.36O6.55 NPs. Furthermore, the Bi3.64Mo0.36O6.55 NP electrode exhibited good cycle stability maintaining over 85 % after 5000 cycles. These results demonstrated Bi3.64Mo0.36O6.55 NPs might be a promising electrode material for pseudocapacitor.
Graphical abstract The fabrication of uniform Bi3.64Mo0.36O6.55 nanoparticles with a diameter of 100 nm were succefully reported by a facial hydrothermal method, which exhibits a extraordinary electronic performance with 998 F g-1 at 1 A g-1 and cycling stability
Li[Ni1/3Co1/3Mn1/3]O2 (NCM 111) is a promising alternative to LiCoO2, as it is less expensive, more structurally stable, and has better safety characteristics. However, its capacity of 155 mAh g?1 is quite low, and cycling at potentials above 4.5 V leads to rapid capacity deterioration. Here, we report a successful synthesis of lithium-rich layered oxides (LLOs) with a core of LiMO2 (R-3m, M?=?Ni, Co) and a shell of Li2MnO3 (C2/m) (the molar ratio of Ni, Co to Mn is the same as that in NCM 111). The core–shell structure of these LLOs was confirmed by XRD, TEM, and XPS. The Rietveld refinement data showed that these LLOs possess less Li+/Ni2+ cation disorder and stronger M*–O (M*?=?Mn, Co, Ni) bonds than NCM 111. The core–shell material Li1.15Na0.5(Ni1/3Co1/3)core(Mn1/3)shellO2 can be cycled to a high upper cutoff potential of 4.7 V, delivers a high discharge capacity of 218 mAh g?1 at 20 mA g?1, and retains 90 % of its discharge capacity at 100 mA g?1 after 90 cycles; thus, the use of this material in lithium ion batteries could substantially increase their energy density.
Graphical Abstract Average voltage vs. number of cycles for the core–shell and pristine materials at 20 mA g?1 for 10 cycles followed by 90 cycles at 100 mA g?1
There is a growing need for the electrode with high mass loading of active materials, where both high energy and high power densities are required, in current and near-future applications of supercapacitor. Here, an ultrathin Co3S4 nanosheet decorated electrode (denoted as Co3S4/NF) with mass loading of 6 mg cm?2 is successfully fabricated by using highly dispersive Co3O4 nanowires on Ni foam (NF) as template. The nanosheets contained lots of about 3～5 nm micropores benefiting for the electrochemical reaction and assembled into a three-dimensional, honeycomb-like network with 0.5～1 μm mesopore structure for promoting specific surface area of electrode. The improved electrochemical performance was achieved, including an excellent cycliability of 10,000 cycles at 10 A g?1 and large specific capacitances of 2415 and 1152 F g?1 at 1 and 20 A g?1, respectively. Impressively, the asymmetric supercapacitor assembled with the activated carbon (AC) and Co3S4/NF electrode exhibits a high energy density of 79 Wh kg?1 at a power density of 151 W kg?1, a high power density of 3000 W kg?1 at energy density of 30 Wh kg?1 and 73 % retention of the initial capacitance after 10,000 charge-discharge cycles at 2 A g?1. More importantly, the formation process of the ultrathin Co3S4 nanosheets upon reaction time is investigated, which is benefited from the gradual infiltration of sulfide ions and the template function of ultrafine Co3O4 nanowires in the anion-exchange reaction.
Graphical abstract The ultrathin 2D Co3S4 nanosheets fabricated on 3D Ni foam and the formation process of the ultrathin Co3S4 nanosheets upon reaction times has been investigated. At the same time, the Co3S4/NF electrode displays an outstanding specific capacitance of 2420 F g?1 at 1 A g?1 with high mass loading of 6 mg cm?2.
Free-standing and flexible NiMoO4 nanorods/reduced graphene oxide (rGO) membrane with a 3D hierarchical structure was successfully synthesized by a general approach including vacuum filtration followed by thermal reduction. NiMoO4 nanorods with about 50–100 nm diameter were embedded homogenously into the 3D rGO sheets and assembled with rGO to form a membrane about 10 μm in thickness. The NiMoO4/rGO membrane could be directly evaluated as anode materials for lithium-ion batteries (LIBs) without using binder. The 3D layer stacked graphene hierarchical architecture can not only offers a continuous conducting framework for efficient diffusion and transport of ion/electron but also accommodates the large volume expansion of NiMoO4 nanorod changes during cycling. Moreover, our results show that the NiMoO4/rGO membrane exhibited excellent electrochemical performance with a high reversible capacity of 945 mAh g?1 at a current density of 0.25 A g?1 as anode materials in LIBs.
In this paper, the LiNi0.5Mn1.5O4 cathode materials of lithium-ion batteries are synthesized by a co-precipitation spray-drying and calcining process. The use of a spray-drying process to form particles, followed by a calcination treatment at the optimized temperature of 750 °C to produce spherical LiNi0.5Mn1.5O4 particles with a cubic crystal structure, a specific surface area of 60.1 m2 g?1, a tap density of 1.15 g mL?1, and a specific capacity of 132.9 mAh g?1 at 0.1 C. The carbon nanofragment (CNF) additives, introduced into the spheres during the co-precipitation spray-drying period, greatly enhance the rate performance and cycling stability of LiNi0.5Mn1.5O4. The sample with 1.0 wt.% CNF calcined at 750 °C exhibits a maximum capacity of 131.7 mAh g?1 at 0.5 C and a capacity retention of 98.9% after 100 cycles. In addition, compared to the LiNi0.5Mn1.5O4 material without CNF, the LiNi0.5Mn1.5O4 with CNF demonstrates a high-rate capacity retention that increases from 69.1% to 95.2% after 100 cycles at 10 C, indicating an excellent rate capability. The usage of CNF and the synthetic method provide a promising choice for the synthesis of a stabilized LiNi0.5Mn1.5O4 cathode material.
Graphical Abstract Micro/nanostructured LiNi0.5Mn0.5O4 cathode materials with enhanced electrochemical performances for high voltage lithium-ion batteries are synthesized by a co-precipitation spray-drying and calcining routine and using carbon nanofragments (CNFs) as additive.
LiMn2O4 is one of the most promising cathode materials due to its high abundance and low cost. However, the practical application of LiMn2O4 is greatly limited owing to its low volumetric energy density. Therefore, increasing its energy density is an urgent problem to be resolved. Herein, using the simple and mass production preferred solid-state reaction, surficial Nb-doped LiMn2O4 composed of the truncated octahedral or spherical-like primary particles are successfully synthesized. Auger electron spectroscopy (AES) and X-ray diffraction (XRD) characterizations confirm that most of Nb5+ enrich in the surficial layer of the particles to form a LiMn2-xNbxO4 phase. This kind of doping can increase the specific discharge capacity of LiMn2O4 materials. Contrast with the pristine LiMn2O4, the discharge capacity of LiMn1.99Nb0.01O4-based 18650R-type battery increases from 1497 to 1705 mAh with the volumetric energy density increasing by ~?13.9%, benefiting from the joint increments of the specific discharge capacity from 119.5 to 123.7 mAh g?1 and the compacted density from 2.81 to 3.10 g cm?3. Furthermore, the capacity retention after 500 cycles at 1 C (1500 mA) is also improved by 17.1%.
CdSe is an important semiconductor for photoelectrochemistry. Here, we propose a two-step method for preparing thin films of aggregated CdSe nanoparticles on Cd electrodes. We first anodized the Cd electrode in an aqueous solution of 0.2 M KNO3 at ?0.9 V (vs. Hg|Hg2SO4(s)|K2SO4 (saturated)) into a porous and layered structure covered with Cd(OH)2 precipitation, and then selenized the Cd(OH)2 deposited on the Cd anode in an aqueous solution of 0.2 M Na2SeSO3. The resulting CdSe nanoparticles self-assembled into strawberry-like nanoaggregates. The anodization time and selenization time were optimized separately. Under our experimental conditions, the optimized anodization time was 80 s, whereas the optimized selenization time ranged from 15 to 60 min, corresponding to the partial or complete conversion of the deposited Cd(OH)2 into smaller and larger strawberry-like CdSe nanoaggregates, respectively. The optimized partially and completely selenized films showed photocurrent responses that were enhanced in different ways but demonstrated comparable performances. They presented an anodic photocurrent density as high as 3.2 mA cm?2 at ?0.3 V with good stability under visible light illumination of 100 mW cm?2 in a solution containing a sacrificial reagent of ascorbic acid.
Graphical Abstract Strawberry-like CdSe nanoaggregates were prepared by selenizing the anodization film of Cd(OH)2 on Cd electrode and they demonstrated enhanced photoelectrochemical performance.
We obtained Tannin-4-azobenzoic acid (azo dye) by the conventional method of diazotization and coupling of aromatic amines. The properties of the azo dye were characterized via ultraviolet-visible (UV–vis), infrared (IR), and nuclear magnetic resonance (NMR) spectroscopy. Nanocrystalline titanium dioxide (TiO2) thin films were deposited by hydrothermal method onto fluorine-doped tin (IV) oxide (FTO)-coated glass substrate at 353 K for 4 h. The as-deposited and annealed films were characterized for structural, morphological, optical, thickness, and wettability properties. The synthesized metal free azo dye was used to sensitize the prepared TiO2 thin film with thickness of 26 μm. The photoelectrochemical (PEC) performance of TiO2 sensitized with the azo dye was evaluated in polyiodide (0.1 M KI + 0.01 M I2 + 0.1 M KCl) electrolyte at 40 mW cm?2 illumination intensity. The cell yielded a short circuit current of 2.82 mA, open circuit voltage of 314.3 mV, a fill factor of 0.30, and a photovoltaic conversion efficiency value of 0.64%.
Sulfonated polyvinylchloride (SPVC) cation-exchange membranes were coated using chitosan solutions comprising different amounts of Fe3O4 nanoparticles. Influence of chitosan immobilization as well as nanofiller concentration on the electrochemical performance of the membranes was investigated. Electrochemical properties of the membranes including permselectivity, ionic permeability, and areal resistance were studied using an equipped electrodialysis setup and NaCl solution as model electrolyte. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were employed for membrane characterization. Electrochemical performance of the SPVC membranes was improved by coating chitosan polymer. In addition, ionic permeability and permselectivity of the membranes were initially raised by increasing nanoparticles concentration from nil to 2 wt% and then decreased by further insertion of the nanofiller. The areal resistance of the plain SPVC membrane was decreased from 9.4 to 2.9 (ohm) by coating of chitosan solution including optimum value of nano-Fe3O4 due to electrical potential field enhancement across the membrane.
LiNi1-x-yCoxMnyO2 (NCM) with excessive lithium is known to exhibit high rate capability and charge–discharge cycling durability. However, the practical usage of NCM is difficult, because the positive electrode slurry is unstable and battery cells swell due to the alkaline residual lithium compound generated on the surface of NCM particles. To reduce the residual lithium compound, ammonium metatungstate (AMT) added to NCM is studied, and the effect is investigated by scanning electron microscopy, aberration-corrected scanning transmission electron microscopy, X-ray diffractometry, synchrotron X-ray diffractometry, and several electrochemical measurements. It is found that the AMT modification reduces the amount of alkaline residual lithium compound and improves the rate capability due to the ~1-nm-thick W-rich layer generated on the NCM surface.
Co2(OH)3Cl xerogel interconnected mesoporous structures have been prepared by a facile one pot sol-gel process and heat treated at 200 and 400 °C. All samples are studied for their morphology, structure, and electrochemical stability upon cycling. The specific capacitance of the as-prepared Co2(OH)3Cl from single electrode study is 450 F/g, when the electrodes are cycled in 3 M KOH at a specific current 2 A/g. Interestingly, capacity retention after 500 and 1000 cycles is about 92 and 75 %, respectively. Sample heated at 200 °C exhibits 308 F/g at 2 A/g and that heated at 400 °C shows only 32 F/g at 0.2 A/g. With an increase in preparation temperature, amorphous Co2(OH)3Cl is converted to crystalline Co3O4 phases with lower electrochemical performance. In full cell study, as-prepared Co2(OH)3Cl showed a capacity of about 49 F/g as asymmetric capacitor and 32 F/g as symmetric capacitor at 2 A/g current density. Co2(OH)3Cl being a novel porous material with merits of homogeneous porosity, high surface area, and an interconnected three dimensional (3D) structure exhibits considerably high capacitance. With a significant specific capacity and electrochemical stability, the synthesized material is a novel potential candidate for supercapacitors.
A series of PANI-CNTs/TiO2 nanotubes/Ti electrodes were fabricated via pulse current co-electrodeposition of polyaniline and functionalized carbon nanotubes onto TiO2 nanotubes/Ti electrodes. FT-IR spectrometry, X-ray photoelectron spectroscopy, and scanning electron microscopy were applied in order to characterize the modified TiO2 nanotubes/Ti electrodes. The morphology studies showed that the PANI-CNTs/TiO2 nanotubes/Ti nanocomposite electrode has many interlaced PANI-CNTs nanorods on the surface of TiO2 nanotubes. The electrochemical measurements of the modified electrodes confirmed that the CNTs in the composite can significantly improve the capacitive behavior as well which have been compared with that of PANI/TiO2 nanotubes/Ti electrodes. The modified electrode exhibited much higher specific capacitance (190 mF cm?2 with 90% retention after 1000 cycles) compared to the PANI/TiO2 nanotubes/Ti (70 mF cm?2 with 77% retention after 1000 cycles) at a current density of 0.85 mA cm?2, indicating its great potential for supercapacitor applications.
Hollow titanium dioxide (TiO2) microspheres were synthesized in one step by employing tetrabutyl orthotitanate (TBOT) as a precursor through a facile solvothermal method in the presence of NH4HCO3. XRD analysis indicated that anatase TiO2 can be obtained directly without further annealing. TiO2 hollow microspheres with diameters in the range of 1.0–4.0 μm were confirmed through SEM and TEM measurements. The specific surface area was measured to be 180 m2 g?1 according to the nitrogen adsorption–desorption isotherms. Superior photocatalytic performance and good lithium storage properties were achieved for resultant TiO2 samples. The H2 evolution rate of the optimal sample is about 0.66 mmol h?1 after loaded with 1 wt.% Pt (20 mg samples). The reversible capacity remained 143 mAh g?1 at a specific current of 300 mA g?1 after 100 charge–discharge cycles. This work provides a facile strategy for the preparation of hollow titanium dioxide microspheres and demonstrates their promising photocatalytic H2 evolution and the lithium storage properties.
Graphical abstract Hollow titanium dioxide spheres are directly synthesized via a facile template-free solvothermal method with the presence of NH4HCO3 based on inside-out Ostwald ripening (see picture), and demonstrated both as a photocatalyst for water splitting and a promising anode material for lithium-ion batteries. Superior photocatalytic performance and excellent lithium storage properties are achieved for resultant TiO2 hollow microspheres.
The effect of dip time variations on electrochemical performance of polypyrrole (PPy)-copper hydroxide hybrid thin-film electrodes was studied well in depth. Synthesis was carried out using a successive ionic layer adsorption and reaction (SILAR) method via an aqueous route, using 0.1 M pyrrole, 0.1 M Cu(NO3)2, and H2O2. The electrochemical analysis was made by using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) analysis, and electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) image of optimized electrode shows nanolamellae-like structures. The characteristic peak observed in Fourier transform infrared (FTIR) analysis at 1558 cm?1 validates the existence of PPy in hybrid electrode material, while the peaks observed at 21.5° and 44.5° in X-ray diffraction (XRD) patterns are evidence for triclinic Cu(OH)2. The observed maximum values of specific capacitance (SC), specific power (SP), specific energy (SE), and coulombic efficiency (η) of the optimized electrode are 56.05 F/g, 10.48 Wh/kg, 11.11 kW/kg, and 46.47%, respectively. For originality and value, the SILAR synthesis of PPy-Cu(OH)2 hybrid thin-film electrodes was carried out for the very first time. Synthesized electrodes showed improved surface structures and electrochemical stability than the pristine PPy electrodes which are necessary for the supercapacitive applications.
A direct adsorption method for the synthesis of Cu2+-doped CdTe quantum dot (QD)-sensitized TiO2 nanotubes (TNTAs) for use as a photoanode is reported in this study. The influences of the molar concentration of Cu2+, the sensitization temperature, the sensitization time, and the loop index on the photovoltaic performance of the CdTe:Cu2+/TNTAswas investigated. Scanning electron microscopy images showed that the CdTe:Cu2+ QDs are well dispersed on the TNTA surface. UV–vis adsorption measurements showed that the visible absorption of the TNTAs was enhanced by the CdTe:Cu2+ QD sensitization. Whereas the power conversion efficiency (PCE) of the bare TNTAs was 0.11%, the maximum PCE of the CdTe:5%Cu2+/TNTAs was 3.70% with a sensitization time of 5.0 h, a sensitization temperature of 60 °C, and a loop index of 2. Therefore, CdTe:5%Cu2+/TNTAs may be employed in quantum-dot-sensitized solar cells.
Graphical abstract The conversion efficiency of the CdTe: 5%Cu2+/TiO2 nanotube arrays can reach a maximum of 3.7%, which is enhanced by 33-fold, on comparison with bare TiO2 nanotube arrays (0.11%).
MoS2 thin films with marigold flower-like nanostructures were grown on conductive fluorine-doped tin oxide (FTO) substrates through a one-step hydrothermal synthesis for their application as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). Different MoS2 thin film samples (A–D) were grown on FTO slides using different concentrations of precursors (sodium molybdate and thioacetamide), while keeping the Mo/S molar ratio constant (1:4.6), in all samples. The effect of varying precursor concentrations (3.2–12.6 mM on MoS2 basis) on the structure of the nanostructured thin films and their performance as DSSC-CEs was investigated. Scanning electron microscopy revealed a material with an infolded petal-like morphology. With increasing precursor concentration, the petal-like structures tended to form bunched nanostructures (100–300 nm) resembling marigold flowers. X-ray diffraction analysis, X-ray photoelectron, and Raman spectroscopy studies showed that the thin films were composed of hexagonal MoS2 with good crystallinity. Hall effect measurements revealed MoS2 to be a p-type semiconductor with a carrier mobility of 219.80 cm2 V?1 s?1 at room temperature. The electrochemical properties of the thin films were examined using cyclic voltammetry and electrochemical impedance spectroscopy. The marigold flower-like MoS2 thin films showed excellent electrocatalytic activity towards the I¯/I3¯ reaction and low charge transfer resistance (Rct) values of 14.77 Ω cm?1, which was close to that of Pt electrode (12.30 Ω cm?1). The maximum power conversion efficiency obtained with MoS2 CE-based DSSCs was 6.32%, which was comparable to a Pt CE-based DSSC (6.38%) under one sun illumination. Similarly, the maximum incident photon-to-charge carrier efficiency exhibited by MoS2 CE-based DSSCs was 65.84%, which was also comparable to a Pt CE-based DSSC (68.38%). The study demonstrated that the marigold flower-like nanostructured MoS2 films are a promising alternative to the conventional Pt-based CEs in DSSCs.
Generally adopted strategies to improve capacitance of the electrode materials are tuning various properties of the electrode material or increasing the cell voltage. While tuning the properties of the electrode material is tedious, increasing the cell voltage is restricted by the stability of the electrolyte. Herein, we report a facile approach to improve the capacitance of MnCO3 by the influence of SiOx nanofluid in the electrolyte. The capacitance properties of MnCO3 are studied in 0.1 M Mg(ClO4)2 electrolyte in the presence and in the absence of SiOx nanofluid. The presence of small amount of SiOx nanofluid in the electrolyte provides higher diffusivity and more conductive percolation paths for ions and thus decreases internal resistance and increases ionic conductivity of the electrolyte. As a result, 60% enhancement in the capacitance is witnessed for MnCO3. Further, nanofluid containing electrolyte is found to be stable over a month.
