Preparation and electrochemical properties of NiO-Co3O4 composite as electrode materials for supercapacitors

Applications of carbon quantum dots in electrochemical energy storage devices

Supercapacitors (SCs), including electric double-layer capacitors (EDLCs), pseudocapacitors, and hybrid capacitors, are esteemed for their high power density and attractive features such as robust safety, fast charging, low maintenance, and prolonged cycling lifespan, sparking significant interest. Carbon quantum dots (CQDs) are fluorescent nanomaterials with small size, broad excitation spectrum, stable fluorescence, and adjustable emission wavelengths. They are widely used in optoelectronics, medical diagnostics, and energy storage due to their biocompatibility, low toxicity, rich surface functional groups, abundant electron-hole pairs, large specific surface area, and tunable heteroatom doping. In this short review, we briefly discussed the advantages and disadvantages of bottom-up and top-down of CQD synthesis methods. The arc-discharge technique, laser ablation technique, plasma treatment, ultrasound synthesis technique, electrochemical technique, chemical exfoliation, and combustion are among the initial top-down approaches. The subsequent section delineates waste-derived and bottom-up methods, encompassing microwave synthesis, hydrothermal synthesis, thermal pyrolysis, and the metal-organic framework template-assisted technique. In addition, this short review focuses on the operational mechanism of supercapacitors, their properties, and the utilization of CQDs in supercapacitors.

Effect of synthesis methods on the activity of NiO/Co3O4 as an electrode material for supercapacitor: in the light of X-ray diffraction study

The formation of heterostructures by combining individual components (NiO and Co3O4) is a preferred approach to enhance electrochemical performance as it leads to improved charge transfer and surface reaction kinetics. In the present work, a NiO/Co3O4 composite was prepared by two methods. First, neat NiO and Co3O4 were prepared by adopting the hydrothermal method followed by the formation of the composite (i) by a hydrothermal route (NC-Hydro) and (ii) by a calcination route (NC-Cal). NC-Hydro composite shows a specific capacity of 176 C g-1 at 1 A g-1 of current density in the three-electrode system in a 2 M KOH solution as an electrolyte with 90% cyclic retention after 5000 cycles at 4 A g-1. NC-Cal shows a specific capacity of 111 C g-1 at 1 A g-1 with 75% cyclic retention. The coulombic efficiency of NC-Hydro was 86.3% while for NC-Cal it was 42.3%. The reason behind the superior electrochemical performance of NC-Hydro in comparison to NC-Cal may be the large interlayer spacing and lattice parameters of the former, which provide large space for redox reactions. The unit cell volume of the composites was more than that of the constituents. This study reveals that the composites prepared by the hydrothermal method have superior electrochemical properties in comparison to composites prepared by the calcination method.

Synthesis and electrochemical properties of nanocubes Mn2SnS3 for high-performance supercapacitors

Exploring environment-friendly active material-electrolyte combinations has become increasingly necessary with the rising use of supercapacitors. In this study, the potential of ternary Mn2SnS3 on Ni foam as an electrode material was considered. The study investigated the impact of precursors on the morphology of the prepared electrodes utilizing techniques such as X-ray diffraction, energy dispersive X-ray analysis, field-emission scanning electron microscopy, and transmission electron microscopy. Nanocubes Mn2SnS3 (NC-MTS) and nanoworms Mn2SnS3 (NW-MTS) were synthesized via a facile solvothermal route. The results suggest that NC-MTS exhibits better capacitive performance compared with NW-MTS, which means that morphology has a significant effect on the electrochemical reaction. NC-MTS presents excellent supercapacitor performances with a high specific capacity of about 2115 F g-1 at current density 2 A g-1, excellent rate capability of 78% at 17 A g-1 and excellent cycling stability 92% capacitance retention after 3000 GCD cycles. Whereas, NW-MTS illustrated a specific capacity of about 853 F g-1 at current density 2 A g-1, rate capability of 50% at 17 A g-1 and cycling stability of 81% capacitance retention after 3000 GCD cycles. Additionally, an asymmetric supercapacitor NC-MTS/NF//AC based on the NC-MTS/NF as a positive electrode and activated carbon (AC) as a negative electrode was successfully constructed with the excellent electrochemical performance, which demonstrated a high energy density of 60.56 Wh kg-1 and a high power density of 699.89 W kg-1.

Nanomaterial-based electrochemical sensors for detection of amino acids

Amino acids are the building blocks of proteins and muscle tissue. They also play a significant role in physiological processes related to energy, recovery, mood, muscle and brain function, fat burning and stimulating growth hormone or insulin secretion. Accurate determination of amino acids in biological fluids is necessary because any changes in their normal ranges in the body warn diseases like kidney disease, liver disease, type 2 diabetes and cancer. To date, many methods such as liquid chromatography, fluorescence mass spectrometry, etc. have been used for the determination of amino acids. Compared with the above techniques, electrochemical systems using modified electrodes offer a rapid, accurate, cheap, real-time analytical path through simple operations with high selectivity and sensitivity. Nanomaterials have found many interests to create smart electrochemical sensors in different application fields e.g. biomedical, environmental, and food analysis because of their exceptional properties. This review summarizes recent advances in the development of nanomaterial-based electrochemical sensors in 2017-2022 for the detection of amino acids in various matrices such as serum, urine, blood and pharmaceuticals.

Electrochemical charge storage performance of mesoporous MoO3@Co3O4nanocomposites as electrode materials

Constructing a novel nanocomposite structure based on Co₃O₄is of the current interest to design and develop efficient electrochemical capacitors. The capacitive performance of MoO₃@Co₃O₄nanocomposite is compared with pristine Co₃O₄nanoparticles, both of them being synthesized by hydrothermal technique. A BET surface area of ∼41 m²g^-1(almost twice that of Co₃O₄) and average pore size of 3.6 nm is found to be suitable for promoting Faradaic reactions in the nanocomposite. Electrochemical measurements conducted on both samples predict capacitive behavior with quasi-reversible redox reactions. MoO₃@Co₃O₄nanocomposite is capable of delivering a superior specific capacitance of 1248 F g^-1at 0.5 A g^-1along with notable stability of 92% even after 2000 cycles of charge-discharge and Coulombic efficiency approaching 100% at 10 A g^-1. The outstanding results obtained in this work assure functional adequacy of MoO₃@Co₃O₄nanocomposite in fabricating high-performance electrochemical capacitors.

A Review of Supercapacitors: Materials Design, Modification, and Applications

Supercapacitors (SCs) have received much interest due to their enhanced electrochemical performance, superior cycling life, excellent specific power, and fast charging–discharging rate. The energy density of SCs is comparable to batteries; however, their power density and cyclability are higher by several orders of magnitude relative to batteries, making them a flexible and compromising energy storage alternative, provided a proper design and efficient materials are used. This review emphasizes various types of SCs, such as electrochemical double-layer capacitors, hybrid supercapacitors, and pseudo-supercapacitors. Furthermore, various synthesis strategies, including sol-gel, electro-polymerization, hydrothermal, co-precipitation, chemical vapor deposition, direct coating, vacuum filtration, de-alloying, microwave auxiliary, in situ polymerization, electro-spinning, silar, carbonization, dipping, and drying methods, are discussed. Furthermore, various functionalizations of SC electrode materials are summarized. In addition to their potential applications, brief insights into the recent advances and associated problems are provided, along with conclusions. This review is a noteworthy addition because of its simplicity and conciseness with regard to SCs, which can be helpful for researchers who are not directly involved in electrochemical energy storage.

Influence of Temperature on ZnO/Co3O4 Nanocomposites for High Energy Storage Supercapacitors

We developed a two-step chemical bath deposition method followed by calcination for the production of ZnO/Co₃O₄ nanocomposites. In aqueous reactions, ZnO nanotubes were first densely grown on Ni foam, and then flat nanosheets of Co₃O₄ developed and formed a porous film. The aspect ratio and conductivity of the Co₃O₄ nanosheets were improved by the existence of the ZnO nanotubes, while the bath deposition from a mixture of Zn/Co precursors (one-step method) resulted in a wrinkled plate of Zn/Co oxides. As a supercapacitor electrode, the ZnO/Co₃O₄ nanosheets formed by the two-step method exhibited a high capacitance, and after being calcined at 450 °C, these nanosheets attained the highest specific capacitance (940 F g^-1) at a scan rate of 5 mV s^-1 in the cyclic voltammetry analysis. This value was significantly higher than those of single-component electrodes, Co₃O₄ (785 F g^-1) and ZnO (200 F g^-1); therefore, the presence of a synergistic effect was suggested. From the charge/discharge curves, the specific capacitance of ZnO/Co₃O₄ calcined at 450 °C was calculated to be 740 F g^-1 at a current density of 0.75 A g^-1, and 85.7% of the initial capacitance was retained after 1000 cycles. A symmetrical configuration exhibited a good cycling stability (Coulombic efficiency of 99.6% over 1000 cycles) and satisfied both the energy density (36.6 Wh kg^-1) and the power density (356 W kg^-1). Thus, the ZnO/Co₃O₄ nanocomposite prepared by this simple two-step chemical bath deposition and subsequent calcination at 450 °C is a promising material for pseudocapacitors. Furthermore, this approach can be applied to other metal oxide nanocomposites with intricate structures to extend the design possibility of active materials for electrochemical devices.

Co3O4 composite nano-fibers doped with Mn4+ prepared by the electro-spinning method and their electrochemical properties

In this work, based on the electrospinning method, pure Co₃O₄, pure MnO₂, and Co₃O₄ composite nano-fiber materials doped with different ratios of Mn⁴⁺ were prepared. XRD, XPS, BET and SEM tests were used to characterize the composition, structure and morphology of the materials. An electrochemical workstation was used to test the electrochemical performance of the materials. The results showed that the material properties had greatly improved on doping Mn⁴⁺ in Co₃O₄ nano-fibers. The relationship between the amount of Mn⁴⁺ doped in the Co₃O₄ composite nano-fiber material and its electrochemical performance was also tested and is discussed in this report. The results show that when n_Co : n_Mn = 20 : 2, the Co₃O₄ composite nano-fiber material had a specific surface area of 68 m² g⁻¹. Under the current density of 1 A g⁻¹, the 20 : 2 sample had the maximum capacitance of 585 F g⁻¹, which was obviously larger than that of pure Co₃O₄ nano-fibers (416 F g⁻¹). After 2000 cycles of charging/discharging, the specific capacitance of the 20 : 2 sample was 85.9%, while that of the pure Co₃O₄ nano-fiber material was only 76.4%. The mechanism of performance improvement in the composite fibers was analyzed, which demonstrated concrete results.

In this work, based on the electrospinning method, pure Co₃O₄, pure MnO₂, and Co₃O₄ composite nano-fiber materials doped with different ratios of Mn⁴⁺ were prepared.

Hydrothermal Synthesized of CoMoO4 Microspheres as Excellent Electrode Material for Supercapacitor

The single-phase CoMoO₄ was prepared via a facile hydrothermal method coupled with calcination treatment at 400 °C. The structures, morphologies, and electrochemical properties of samples with different hydrothermal reaction times were investigated. The microsphere structure, which consisted of nanoflakes, was observed in samples. The specific capacitances at 1 A g^-1 are 151, 182, 243, 384, and 186 F g^-1 for samples with the hydrothermal times of 1, 4, 8, 12, and 24 h, respectively. In addition, the sample with the hydrothermal time of 12 h shows a good rate capability, and there is 45% retention of initial capacitance when the current density increases from 1 to 8 A g^-1. The high retain capacitances of samples show the fine long-cycle stability after 1000 charge-discharge cycles at current density of 8 A g^-1. The results indicate that CoMoO₄ samples could be a choice of excellent electrode materials for supercapacitor.

Controlled synthesis of Pt and Co3O4 dual-functionalized In2O3 nanoassemblies for room temperature detection of carbon monoxide

Innovative Pt and Co₃O₄ nanostructure co-decorated In₂O₃ nanobundles have been successfully developed and demonstrated as high-performance room-temperature CO gas sensors.

MoO2/Mo2N hybrid nanobelts doped with gold nanoparticles and their enhanced supercapacitive behavior

AuNPMoON-nanobelts with a width of 200 nm and an Au content of 1.08 wt% show a capacitance of 348 F g⁻¹.

Electrochemical properties of NiCoO2 synthesized by hydrothermal method

NiCoO₂ microspheres were successfully synthesized via an easy hydrothermal method, followed by an annealing process at 350 °C under a nitrogen atmosphere.