A Facile Preparation of Zinc Cobaltite (ZnCo2O4) Nanostructures for Promising Supercapacitor Applications

Hybrid nanocomposites have shown their excellent potential in energy storage devices particularly in electrochemical supercapacitors to meet the forthcoming demand in the energy sector applications. Novel hybrid composited displayed the dual nature of electrochemical double layer and pseudocapacitive behaviour, which makes them more advantageous in supercapacitor device fabrication. Zinc cobaltite (ZnCo₂O₄) nanostructures have been prepared by precipitation route and the structural, optical and electrochemical properties of the final product were analyzed. X-ray pattern showed the spinal cubic phase structure with fine nano-crystallites. The FTIR and Raman spectrum confirmed the presence of surface functional groups and confirmed the formation of high-quality ZnCo₂O₄ nanocrystals. XPS and EDX spectrum showed the high purity and good crystallinity nature of the as-prepared ZnCo₂O₄ nanocrystal. FE-SEM and TEM analysis exhibits the bundle like morphology of the final product. Finally, the as-prepared ZnCo₂O₄ nanostructure was investigated by cyclic voltammetry (CV), galvanic charge–discharge analysis (GCD) and electrochemical impedance spectroscopy (EIS) to check its suitability. The electrochemical investigation demonstrated the highest capacitance of 159 F g^?1 at 2 mA cm^?2 in 2 M KOH electrolyte and the long cyclic test showed the 92% initial capacitance retention over 2500 cycles. It reveals/demonstrated that the spinel ZnCo₂O₄ nanostructures own a promising usage in devices for electrochemical energy storage.

     

Rational design of binder-free ZnCo2O4 and Fe2O3 decorated porous 3D Ni as high-performance electrodes for asymmetric supercapacitor

The development of hierarchical, porous film based current collector has created huge interest in the area of energy storage, sensor, and electrocatalysis due to its higher surface area, good electrical conductivity and increased electrode-electrolyte interface. Here, we report a novel method to prepare a hierarchically ramified nanostructured porous thin film as a current collector by dynamic hydrogen bubble template electro-deposition method. At a first time, we report a porous 3D-Ni decorated with ZnCo₂O₄ and Fe₂O₃ by simple, low-cost electrochemical deposition method. The fabricated porous 3D-Ni based electrodes showed an excellent electrochemical property such as high specific capacitance, excellent rate capability, and good cycle stability. The asymmetric solid-state supercapacitor device was fabricated using porous, 3D Ni decorated with ZnCo₂O₄ and Fe₂O₃ as the positive and negative electrodes. The fabricated ZnCo₂O₄//Fe₂O₃ asymmetric device delivered an areal capacitance of 92?mF?cm^?2 at a current density of 0.5?mA?cm^?2 with a maximum areal power density of 3?W?cm^?2 and areal energy density of 28.8?mWh?cm^?2. The higher performances of porous, 3D current collector have a huge potential in the development of high performance supercapacitor.     

Constructing ZnCo2O4@LDH Core–Shell hierarchical structure for high performance supercapacitor electrodes

In this article, ZnCo₂O₄ nanowires deposited with two kinds of typical layered double hydroxides (Ni–Al,Co–Al LDH) are developed via scalable method. Two materials all display core–shell hierarchical structure. High specific capacitance of 2041 F g⁻¹ and 1586 F g⁻¹ are obtained for ZnCo₂O₄@Co–Al LDH and ZnCo₂O₄@Ni–Al LDH,respectively. Combining with active surface and synergistic effect, the role of hierarchical structure in enhancing performance is revealed. Moreover, two all solid state supercapacitors based on fabricated materials as positive electrodes, activated carbon as negative electrodes and PVA–KOH as polymer electrolyte are assembled. The maximum power and energy densities of ZnCo₂O₄@Co–Al LDH//AC are 6200 W kg⁻¹ and 50.1 Wh kg⁻¹, respectively. While the power and energy densities of ZnCo₂O₄@Ni–Al LDH//AC are 3400 W kg⁻¹ and 27.8 Wh kg⁻¹. At last, an energy storage–conversion system, based on solar cell as input device and assembled asymmetric supercapacitor ZnCo₂O₄@Co–Al LDH//AC as output device, is integrated as a self–sustaining power device, indicating its potential in practical applications.     

Reduced graphene oxide/hierarchal spinel nickel cobaltite nanoflowers composites for supercapacitor electrodes with ultrahigh capacitive and excellent rate performance

Researchers are extensively investigating transition metal oxides due to their unique porous architectural structure and remarkable electrochemical properties, which are suitable to boost the energy storage capabilities. In present work, facile chemical route was used to synthesize hierarchal spinel nickel cobaltite nanoflowers anchored reduced graphene oxide (NiCo₂O₄-rGO) as high performance electrode material. NiCo₂O₄ anchored rGO demonstrated specific capacitance of 2695 Fg^-1 at 1 Ag^-1, which is greater than pristine NiCo₂O₄ nanoflowers specific capacitance. NiCo₂O₄-rGO showed excellent stability and retention capability of 96% after 2500 cycles at 5 Ag^-1. Furthermore, NiCo₂O₄–rGO exhibited maximum energy density of 93.57 WhKg^?1 at power density of 250 WKg^-1. We have achieved specific capacitance and retention capability which is higher than previously reported results. This enhancement is mainly attributed to the spinel structure of NiCo₂O₄ and its robust structural affinity with rGO. Moreover, rGO possesses extended surface area provided ample of active sites and exceptional synergetic effect which helped to enhance the induction and consequently transportation of e^?/h⁺. More importantly due to its special morphological effects, in future NiCo₂O₄ anchored rGO nanoflowers may open new avenue in research but also used as an efficient electrode material for the construction of high performance supercapacitors.     

Sol-gel synthesis,characterization, and supercapacitor applications of MCo2O4 (M = Ni,Mn, Cu,Zn) cobaltite spinels

High performance MCo₂O₄spinels (M = Ni, Mn, Cu, Zn) were synthesized by the sol gel method (citrate) and their capacitive behavior was investigated in alkaline electrolyte. Their structural, morphological, functional groups and textural properties were characterized by TG/DSC, XRD, SEM, FTIR, EDS and BET. The capacitive properties of spinel MCo₂O₄ samples were thoroughly investigated in 1?M KOH aqueous electrolyte using cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The results revealed high stability of the samples and excellent electrochemical reversibility, and exhibited specific capacity depending on the nature of the transition metal ion M. A high specific capacitance of 285?F?g^?1 was measured for CuCo₂O₄ and a low capacitance of 158?F?g^?1 for ZnCo₂O₄.In addition, MCo₂O₄ spinels displayed good stability during long-term cycles with a cycling efficiency which exceeds75% after 1000 cycles. The obtained results classified MCo₂O₄ cobaltite spinels as most promising materials for their application in super capacitors.     

Investigating the pseudo – Capacitive properties of interlayer engineered VOPO4 by organic molecule intercalation

The varying oxidation states of vanadium has given vanadium phosphate-based compounds a very rich chemistry, that has resulted in increasing interest in them for varying applications such as energy storage systems, including supercapacitors. Among them is vanadyl phosphates that exist in several polymorphs and have seen lots of research on their applications in alkali metal rechargeable batteries. Layered VOPO₄ is of much interest due to its ability to undergo intercalation reaction. In this work, an organic molecule (triethylene glycol) was successfully intercalated into the layers of VOPO₄ in a two-step solvothermal reaction. This approach resulted in exfoliation of VOPO₄ layers leading to enlarged interlayer spacing, as well as enhancing the conductivity by reducing the band gap of the material. The intercalated material (TrEG-VOP) demonstrated an enhanced supercapacitor properties with capacitance 473 Fg^-1 and capacitance retention of 80% against capacitance 400 Fg^-1 and capacitance retention of 55% for the pristine (VOP)     

The effects of urea concentration on microstructures of ZnCo2O4 and its supercapacitor performance

The effects of urea concentration on microstructures of ZnCo₂O₄ during hydrothermal process and their supercapacitors performance were investigated. The sphere ZnCo₂O₄ oxide with nanostructure arrays was formed after hydrothermal process containing low urea concentration. The slim and curved ZnCo₂O₄ nanowires were formed on Ni foam due to medium urea concentration, while sharp and separated ZnCo₂O₄ nanostructure arrays were formed on Ni foam due to high urea concentration. The sharp and separated ZnCo₂O₄ nanostructure arrays on Ni foam showed the best electrochemical performance. ZnCo₂O₄ nanostructure arrays obtained were composed of interconnected ZnCo₂O₄ nanoparticles. The gaps between ZnCo₂O₄ nanoparticles promoted penetration of the electrolyte, which induced the high supercapacitive performance. The sharp and separated ZnCo₂O₄ nanostructure arrays on Ni foam had the lowest charge transfer resistance, which improved supercapacitive performance. In addition, the strong and separated ZnCo₂O₄ nanowires improved significantly cycle life during the charge-discharge process due to good strain accommodation of the unique structure.     

One-pot hydrothermal synthesis of Mn3O4 nanorods grown on Ni foam for high performance supercapacitor applications

Mn₃O₄/Ni foam composites were synthesized by a one-step hydrothermal method in an aqueous solution containing only Mn(NO₃)₂ and C₆H₁₂N₄. It was found that Mn₃O₄ nanorods with lengths of 2 to 3 μm and diameters of 100 nm distributed on Ni foam homogeneously. Detailed reaction time-dependent morphological and component evolution was studied to understand the growth process of Mn₃O₄ nanorods. As cathode material for supercapacitors, Mn₃O₄ nanorods/composite exhibited superior supercapacitor performances with high specific capacitance (263 F · g^-1 at 1A · g^-1), which was more than 10 times higher than that of the Mn₃O₄/Ni plate. The enhanced supercapacitor performance was due to the porous architecture of the Ni foam which provides fast ion and electron transfer, large reaction surface area, and good conductivity.     

Nanoengineering of ZnCo2O4@CoMoO4 heterogeneous structures for supercapacitor and water splitting applications

A hybrid ZnCo₂O₄@CoMoO₄ heterogeneous structure deposited onto nickel foam was synthesized via a two-step hydrothermal process. The results demonstrate that the hybrid architecture exhibits excellent electrochemical performance, including the specific capacitance of 1040C g^?1 at 1 A g^?1 for hybrid structures, high energy density of 87.3 Wh kg^?1 at a power density of 2700 W kg^?1 for an as-assembled supercapacitor and excellent cycle stability with a capacity retention of 99% undergoing 8000 charge-discharge for the device. Moreover, it also shows favorable electrocatalytic activity with low overpotentials of 237 mV at 20 mA cm^?2 for oxygen evolution reaction and 114 mV at 10 mA cm^?2 for hydrogen evolution reaction, and low cell voltage of 1.54 V at 10 mA cm^?2 for overall water splitting. In addition, the stability maintains well for the long-term use of 13 h. We believe that this hybrid ZnCo₂O₄@CoMoO₄ heterogeneous structure could be a promising candidate for future energy storage and conversion.     

MWCNTs-GONRs/Co3O4 electrode with needle-like arrays for outstanding supercapacitors

Multiwalled carbon nanotubes-graphene oxide nanoribbons (MWCNTs-GONRs) exhibit high specific surface area and good electroconductivity because of their unique three-dimensional cross-linking structure with the properties of both CNTs and GONRs. In this study, a hydrothermal method was employed to anchor MWCNTs–GONRs onto a Ni foam (NF) to obtain a precursor substrate. Subsequently, Co₃O₄ arrays were grown on the NF substrate to synthesize a MWCNTs–GONR/Co₃O₄ electrode. The electrode showed a capacitance of 846.2 F g⁻¹ at 1 A g⁻¹ and a capacitance retention of 90.1% after 3000 cycles. Furthermore, MWCNTs–GONRs/Co₃O₄ and active carbon (AC) were used as the positive and negative electrodes, respectively, to assemble a supercapacitor, which delivered a maximum energy density of 38.23 W h kg⁻¹ and a high power density of 6.80 kW kg⁻¹. In addition, the specific capacitance of the device reached a maximum of 91.5% after 9000 cycles. Thus, the MWCNTs–GONRs/Co₃O₄ electrode showed huge potential for supercapacitor applications.     

Electrochemical performance of activated carbon-supported vanadomolybdates electrodes for energy conversion

Reinforcing polyoxomolybdates (POMs) into the activated carbon (AC) template engenders a nanohybrid electrode material for high-performance supercapacitor applications. Herein, a first-time novel integration of two polyoxometalates ([PVMo₁₁O₄₀]^4-, [PV₂Mo₁₀O₄₀]^5-) with AC has been demonstrated, and their structural and electrochemical performances were analyzed. AC-VMo₁₁ composite displayed an enhanced capacitance of 450 Fg^-1 with an improved energy density of 59.7 Whkg^-1. Furthermore, the symmetric supercapacitor cell for AC-VMo₁₁ and AC-V₂Mo₁₀ showed high cell capacitances of 38.8 and 20.01 mF, respectively, alongside 99.99% capacitance retention of over 5000 cycles. In addition, the influence of ionic liquid as an electrolyte on AC-V₂Mo₁₀ based supercapacitor cell was investigated in tetrabutylammonium bromide (TBAB) electrolyte solution.     

Structural and electrochemical properties of mixed calcium-zinc spinel ferrites nanoparticles

In the current work, we provide the electrochemical (EC) characteristics and considerable size of Ca-doped ZnFe₂O₄ nanoparticles. Mixed transition metal oxides are widely used as excellent electrode materials in superior supercapacitors because of their superior capacitance, low cost, and environmental friendliness. The prepared nanoparticles were characterized by X-ray diffraction (XRD), Field-emission scanning electron microscope (FE-SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), and EC methods. The results exhibited that the as-synthesized nanoparticles had a cubic spinel crystal structure and efficient EC properties. The EC properties of the prepared electrodes were explored by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) studies. The Ca_0.1Zn_0.9Fe₂O₄ electrode demonstrated a specific capacitance (SC) ～208 Fg^-1 at a 2 mV/s scan rate due to significant morphological behavior. Therefore may be the prepared materials are the finest electrodes for supercapacitor applications.     

High-performance binder-free supercapacitor electrode by direct growth of cobalt-manganese composite oxide nansostructures on nickel foam

A facile approach composed of hydrothermal process and annealing treatment is proposed to directly grow cobalt-manganese composite oxide ((Co,Mn)₃O₄) nanostructures on three-dimensional (3D) conductive nickel (Ni) foam for a supercapacitor electrode. The as-fabricated porous electrode exhibits excellent rate capability and high specific capacitance of 840.2 F g^-1 at the current density of 10 A g^-1, and the electrode also shows excellent cycling performance, which retains 102% of its initial discharge capacitance after 7,000 cycles. The fabricated binder-free hierarchical composite electrode with superior electrochemical performance is a promising candidate for high-performance supercapacitors.     

ZnCo2O4/CNT composite for efficient supercapacitor electrodes

Due to their combination of enhanced electrical conductivity and high-performance electron and ion transport channels, binary metal oxides with well-morphological optimized electrode materials have been attracted the greatest research attention for high-performance supercapacitor applications. An easy co-precipitation method is used to synthesize ZnCo₂O₄ nanoparticles using NaOH and Urea as precipitation agents. To facilitate electrical conductivity, suitable carbon material such as carbon nanotube (CNT) has been added to make a composite material. The three-electrode system was preferred for estimating specific capacitance of prepared material and optimally efficient ZnCo₂O₄/CNT electrode delivered a moderate 888 F/g capacitance at 1 A/g in 3 M KOH and after 5000 charge discharge cycles 94.72% of cycling stability retained at 5 A/g. This paper presents a little price and simple procedure for preparation of ZnCo₂O₄/CNT electrode that promotes creative sprit for energy storage applications.     

Tailoring cobalt oxide nanostructures for stable and high-performance energy storage applications

Different micro- and nanostructures of cobalt oxide are grown on Ni foam using surface-modifying agents via a simple one-pot hydrothermal synthesis process with the help of surface modifying agents. The structural, chemical, morphological, and electrochemical properties are systematically investigated using a potentiostat, X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) analysis. The pristine Co₃O₄, cetyltrimethyl ammonium bromide (CTAB) mediated Co₃O₄, and Triton X-100 mediated Co₃O₄ form the chestnut bur flower, dandelion flower, and star anise-like morphology, respectively. The electrochemical measurements demonstrate that interconnected nanonetwork of dandelion flower-like morphology obtained via CTAB delivers the highest specific capacitance of 521.63 F g^?1. Since an interconnected network provides the channel path for high electronic conductivity and low diffusion resistance, the fabricated electrode provides excellent electrochemical stability over the 3000 charge-discharge cycles. It retains 95.29% of the initial capacitance after 3000 charge-discharge cycles. The result proved that surface modification of Co₃O₄ material improved the charge storage performance of electrodes for supercapacitor applications.     

Enhancing the performance and stability of NiCo2O4 nanoneedle coated on Ni foam electrodes with Ni seed layer for supercapacitor applications

We introduce a facile way to improve the performance of NiCo₂O₄ electrode by including a Ni seed layer. The seed layer deposited on Ni foam electrode (NiCo₂O₄/Ni@NF) shows the superior specific capacity of 1142 C g⁻¹ at 1 A g⁻¹ with the excellent cycle stability of ∼96% even after 5000 cycles at a higher current density of 5 A g⁻¹. These values are about 3.7 times higher than that of the electrode (NiCo₂O₄@NF) without a seed layer, which shows the specific capacity of 305 C g⁻¹@1 A g⁻¹ with cycle stability of 84% even at a lower current density of 1 A g⁻¹. The enhanced performance of the NiCo₂O₄/Ni@NF electrode may be attributed to lower interface resistance, fast redox reversible reaction, and improved surface active sites. Further, the asymmetric solid-state supercapacitor device is fabricated by using the NiCo₂O₄/Ni@NF electrode as a positive and reduced graphene oxide (rGO)-Fe₂O₃ nanograin as a negative electrode with PVA-KOH gel electrolyte, and the NiCo₂O₄/Ni20@NF//rGO-Fe₂O₃@NF asymmetric solid state device delivers an areal capacitance of 446 mF cm⁻² with a low capacitance loss of 18% even after 10000 cycles. Further, the fabricated asymmetric solid state device shows a maximum energy density of 124.3 Wh cm⁻² (at 3.58 kW cm⁻²) and power density of 14.88 kW cm⁻² (at 31.41 Wh cm⁻²).     

Facile Fabrication of Binder-Free CoZn LDH/CFP Electrode with Enhanced Capacitive Properties for Asymmetric Supercapacitor

CoZn layered double hydroxide (LDH) or Co(OH)₂ pseudocapacitive material has been prepared on the current collector of carbon fiber paper (CFP) using an eco-friendly one-step electrodeposition. Benefiting from its unique structural feature, the binder-free CoZn LDH/CFP electrode material realizes high specific capacitance of 1156 Fg^?1 at a current density of 1 Ag^?1 and excellent rate capability of 80% retention with 16 fold current density increment, which is much better than that of Co(OH)₂ (617 Fg^?1, 65%). Notably, the CoZn LDH/CFP can retain an outstanding electrochemical stability with a capacitance degradation of only 6% after 6000 charge–discharge cycles at 32 Ag^?1. Moreover, an asymmetric supercapacitor (ASC) using CoZn LDH/CFP as a positive electrode and AC/CFP as a negative electrode has been assembled. The ASC exhibits a superior energy density of 30.0 Whkg^?1 at a power density of 800 Wkg^?1 with a specific capacitance up to 84.4 Fg^?1 and a potential window wide to 1.6 V. These encouraging results indicate that CoZn LDH/CFP composite material has a great potential for next-generation energy conversion/storage devices.

     

Polyaniline grafted chitosan/GO-CNT/Fe3O4 nanocomposite as a superior electrode material for supercapacitor application

Developing appropriate stable electroactive electrode materials for supercapacitor application is the challenging issue, which attracts enormous attention in recent decades. In this regard, Fe₃O₄ nanoparticles are firstly synthesized on chitosan/graphene oxide-multiwall carbon nanotubes (CS/GM/Fe₃O₄). Then, polyaniline (PANI) is grafted on it via in situ chemical polymerization and named as CS/GM/Fe₃O₄/PANI. The as-prepared nanocomposites are characterized by Field emission scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and energy dispersive X-ray spectroscopy. The capacitive properties of the electrodes are investigated in a three electrode configuration in 0.5 M Na₂SO₄ electrolyte by various electrochemical techniques. The specific capacitance of CS/GM/Fe₃O₄/PANI electrode is 1513.4 Fg⁻¹ at 4 Ag⁻¹ which is 1.9 times higher than that of CS/GM/Fe₃O₄ (800 Fg⁻¹). Meanwhile, the electrodes exhibit appropriate cycle life along with 99.8% and 93.95% specific capacitance at 100 Ag⁻¹ for chitosan/GO-CNT/Fe₃O₄ and polyaniline grafted chitosan/GO-CNT/Fe₃O₄, respectively.     

Enhanced sunlight driven photocatalytic activity and electrochemical sensing properties of Ce-doped MnFe2O4 nano magnetic ferrites

This research deals with the facile combustion synthesis of manganese ferrite (MFO) nanoparticle with different cerium concentration and their potential application as an efficient photocatalyst and chemical sensor. The concentration of introduced cerium affects the size, structure, compositional, morphological, optical, photoluminescence and magnetic properties of the ferrite nanoparticle. The X-ray diffraction pattern affirmed the arrangement of cubic spinel structure with the formation of secondary phase CeO₂ as the cerium concentration exceed 3 mol%. SEM micrographs revealed irregular morphology with more number of pores and voids. HRTEM along with SAED pattern revealed the crystalline cubic nature. The optical band gap deduced from UV–Vis-DRS spectra was observed to be in the range 2.3–2.8 eV. PL studies indicated a significant minimization in combination of electrons & holes in MnFe₂O₄ on addition of Ce dopant. VSM investigation demonstrated the soft magnetic nature of the prepared sample with moderate magnetization value. An excellent photocatalytic performance of Cerium doped MFO (3 mol%) towards MB and AR dye degradation was found to be 1.5 and 1.67 times more compared to host matrix under Sunlight irradiation that correlated to reduced band gap, Ce dopant and efficient separation of charge carriers. Cerium doped MFO (3 mol%) have high specific capacitance value of 471.7 and 1546.8 Fg^-1 for NaNO₃ and HCl electrolytes respectively, indicating the pseudo capacitance nature due to which it can be used as a supercapacitor. The synthesized nanoparticles can sense d-Glucose and Paracetamol even at a lower concentration varying from 1 to 10 mM. The synthesized Ce-doped MnFe₂O₄ nanomaterials have great potential to be used in the future production of promising active photocatalysts and sensitive chemical sensors for the identification and degradation of toxic industrial dyes for improved safety in the fields of environment and health care.     

Synthesis of rGO/nanoclay/PVK nanocomposites,electrochemical performances of supercapacitors

ABSTRACT

In this study, graphene oxide (GO) was chemically reacted with sodium borohydride (NaBH₄) to form reduced graphene oxide (rGO). rGO, Montmorillonite nanoclay, and polyvinylcarbazole (PVK) were used to form a ternary nanocomposite via chemical reaction. These nanocomposite qualities were described via scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), Fourier transform infrared spectroscopy-attenuated transmission reflectance (FTIR-ATR). In addition, these materials were used in supercapacitor device as an active material to test electrochemical performances via cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). The rGO/nanoclay/PVK nanocomposite shows significantly improved specific capacitance (C_sp = 168.64 Fg^?1) compared to that of rGO (C_sp = 63.26 Fg^?1) at the scan rate of 10 mVs^?1 by CV method. The enhanced capacitance results in high power density (P = 5522.6 Wkg^?1) and energy density (E = 28.84 Whkg^?1) capabilities of the rGO/nanoclay/PVK nanocomposite material. The addition of nanoclay and PVK increased the specific capacitance of rGO material due to a dopant effect for supercapacitor studies. Ragone plots were drawn to observe energy and power density of supercapacitor devices. The C_sp of rGO/nanoclay/PVK nanocomposite has only 86.4% of initial capacitance for charge/discharge performances obtained by CV method for 5000 cycles.