Facile synthesis of Mn-doped NiCo2O4 nanoparticles with enhanced electrochemical performance for a battery-type supercapacitor electrode

Research Progress in the Preparation of Transition Metal Sulfide Materials and Their Supercapacitor Performance

Transition metal sulfides are widely used in supercapacitor electrode materials and exhibit excellent performance because of their rich variety, low price, and high theoretical specific capacity. At present, the main methods to prepare transition metal sulfides include the hydrothermal method and the electrochemical method. In order to further improve their electrochemical performance, two aspects can be addressed. Firstly, by controllable synthesis of nanomaterials, porous structures and large surface areas can be achieved, thereby improving ion transport efficiency. Secondly, by combining transition metal sulfides with other energy storage materials, such as carbon materials and metal oxides, the synergy between different materials can be fully utilized. However, future research still needs to address some challenges. In order to guide further in-depth research, it is necessary to combine the current research-derived knowledge and propose a direction for future development of transition metal sulfide electrode materials.

Mesoporous Mn-substituted MnxZn1-xCo2O4 ternary spinel microspheres with enhanced electrochemical performance for supercapacitor applications

Extensive investigations have been carried out on spinel mixed transition metal oxide-based materials for high-performance electrochemical energy storage applications. In this study, mesoporous Mn-substituted MnxZn1-xCo2O4 (ZMC) ternary oxide microspheres (x = 0, 0.3, 0.5, 0.7, and 1) were fabricated as electrode materials for supercapacitors through a facile coprecipitation method. Electron microscopy analysis revealed the formation of microspheres comprising interconnected aggregates of nanoparticles. Furthermore, the substitution of Mn into ZnCo2O4 significantly improved the surface area of the synthesized samples. The electrochemical test results demonstrate that the ZMC3 oxide microspheres with an optimal Mn substitution exhibited enhanced performance, displaying the largest specific capacitance of 589.9 F g-1 at 1 A g-1. Additionally, the ZMC3 electrode maintained a capacitance retention of 92.1% after 1000 cycles and exhibited a significant rate capability at a current density of 10 A g-1. This improved performance can be ascribed to the synergistic effects of multiple metals resulting from Mn substitution, along with an increase in the surface area, which tailors the redox behavior of ZnCo2O4 (ZC) and facilitates charge transfer. These findings indicate that the incorporation of Mn into mixed transition metal oxides holds promise as an effective strategy for designing high-performance electrodes for energy storage applications.

Multiprocessing Substrates Enhanced Ta2O5/NiCo2O4 Spinel Nanocomposites for Effective Electro-/Photocatalytic and Toxicological Effects via the Caenorhabditis elegans Model

NiCo2O4 spinel composites decorated with metal oxides (Ta2O5), reduced graphene oxide (rGO), polyaminoanthraquinone (PAAQ), and layered double hydroxide hydrotalcite (HTs) were synthesized by the hydrothermal route. The synthesized composites were characterized using X-ray powder diffraction (XRD), Brunauer-Emmett-Teller (BET), high-resolution transmission electron microscopy (HR-TEM), and X-ray photoelectron spectroscopy (XPS) analyses for structural parameters such as surface area, morphology, chemical composition, etc. The production of oxygen by the water oxidation technique is the most suitable eco-friendly method, where rGO@Ta2O5/NiCo2O4 (RTNCO) showed an efficient oxygen evolution reaction (OER) performance under 1 M KOH electrolyte. Lower Tafel slope and overpotential values of 76 mV dec-1 and 315 mV, respectively, were calculated for RTNCO. The photocatalytic degradation efficiencies calculated were MB = 97.86%, RhB = 94.75%, and AP = 96% under UV light illumination within 120 min. The degraded dye solution was tested on mung bean (Vigna radiata) plants to determine the toxicity of the dye solution after 15 days, and the results showed good seed germination similar to that in water as the control. The synthesized materials exhibited better antibacterial activity against Bacillus cereus, Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli. Interestingly, the toxicological effects of the degraded dyes and drug solutions were effectively studied in the Caenorhabditis elegans model. The overall results revealed that the synthesized composites are promising for electro-/photocatalytic and biological applications.

Carbon cloth supporting spinel CuMn0.5Co2O4 nanoneedles with the regulated electronic structure by multiple metal elements as catalysts for efficient oxygen evolution reaction

Developing transition metal oxide catalysts to replace the noble metal oxide catalysts for efficient oxygen evolution reaction (OER) is essential to promote the practical application of water splitting. Herein, we designed and constructed the carbon cloth (CC) supporting spinel CuMn_0.5Co₂O₄ nanoneedles with regulated electronic structure by multiple metal elements with variable chemical valences in the spinel CuMn_0.5Co₂O₄. The carbon cloth not only provided good conductivity for the catalytic reaction but also supported the well-standing spinel CuMn_0.5Co₂O₄ nanoneedles arrays with a large special surface area. Meanwhile, the well-standing nanoneedles arrays and mesoporous structure of CuMn_0.5Co₂O₄ nanoneedles enhanced their wettability and facilitated access for electrolyte to electrochemical catalysis. Besides, the regulated electronic structure and generated oxygen vacancies of CuMn_0.5Co₂O₄/CC by multiple metal elements improved the intrinsic catalytic activity and the durability of OER activity. Profiting from these merits, the CuMn_0.5Co₂O₄/CC electrode exhibited superior OER activity with an ultralow overpotential of 189 mV at the current density of 10 mA⋅cm^-2 and a smaller Tafel slope of 64.1 mV⋅dec^-1, which was competitive with the noble metal oxides electrode. And the CuMn_0.5Co₂O₄/CC electrode also exhibited long-term durability for OER with 95.3% of current retention after 1000 cycles. Therefore, the competitive OER activity and excellent cycling durability suggested that the CuMn_0.5Co₂O₄/CC electrode is a potential candidate catalyst for efficient OER.

Molybdenum doped induced amorphous phase in cobalt acid nickel for supercapacitor and oxygen evolution reaction

Reasonable structural design and metal-doping play significant roles in the optimization of electrochemical energy storage and conversion. Herein, in situ growth of Molybdenum-doped amorphous cobalt acid nickel nanoneedles on Ni foam (Mo-NiCo₂O₄/NF) has been successfully synthesized by a simple hydrothermal-annealing strategy. Benefiting from the unique hierarchical nanostructures and doping-optimized electronic structural configuration, the cross-link network structure of Mo-doped amorphous NiCo₂O₄ with large specific surface areas exhibit excellent supercapacitor performance and electrocatalytic activity. As expected, the optimized Mo-doped NiCo₂O₄ samples possess a specific capacitance of 3970 mF cm^-2 at 1 mA cm^-2 and remarkable rate performance. The assembled hybrid supercapacitor obtains a maximum energy density of 35 Wh kg^-1 (420 W kg^-1) and keeps a capacitance retention of 107% after 5000 cycles. As an electrocatalyst, Mo-NiCo₂O₄/NF shows a rapid self-reconstruction process during oxygen evolution reaction (OER) that produces rich oxygen vacancies and thus exhibits remarkable long-term stability. The nanocomposites exhibit small overpotential (280 mV at 10 mA cm^-2) and Tafel slope (43 mV dec^-1). These results strongly demonstrate that both local amorphous phase and porous hierarchical structure design from Mo dopant provide superiorities for the synthesis of efficient and stable multifunctional electrode materials for energy storage and conversion.

Effect of Mn2+ incorporation on the photoelectrochemical properties of BiVO4

Mn2+–BiVO4 photoanodes (Mn2+ = 0.2–1%) to improve the charge-carrier separation and electrical conductivity of BiVO4 are reported.

Quasi-anisotropic benefits in electrospun nickel–cobalt–manganese oxide nano-octahedron as anode for lithium-ion batteries

A polyhedral Ni–Co–Mn–O nano-octahedron anode for lithium-ion batteries was synthesized, which demonstrated enhanced lithium storage properties as compared to the nanofiber counterpart.

MnCo2O4/Ni3S4 nanocomposite for hybrid supercapacitor with superior energy density and long-term cycling stability

MnCo₂O₄ is regarded as a good electrode material for supercapacitor due to its high specific capacity and good structural stability. However, its poor electrical conductivity limits its wide-range applications. To solve this issue, we integrated the MnCo₂O₄ with Ni₃S₄, which has a good electrical conductivity, and synthesized a MnCo₂O₄/Ni₃S₄ nanocomposite using a two-step hydrothermal process. Comparing with individual MnCo₂O₄ and Ni₃S₄, the MnCo₂O₄/Ni₃S₄ nanocomposite showed a higher specific capacity and a better cycling stability as the electrode for the supercapacitor. The specific capacity value of the MnCo₂O₄/Ni₃S₄ electrode was 904.7 C g^-1 at 1 A g^-1 with a potential window of 0-0.55 V. A hybrid supercapacitor (HSC), assembled using MnCo₂O₄/Ni₃S₄ and active carbon as the cathode and anode, respectively, showed a capacitance of 116.4 F g^-1 at 1 A g^-1, and a high energy density of 50.7 Wh kg^-1 at 405.8 W kg^-1. Long-term electrochemical stability tests showed an obvious increase of the HSC's capacitance after 5500 charge/discharge cycles, reached a maximum value of ∼162.7% of its initial value after 25,000 cycles, and then remained a stable value up to 64,000 cycles. Simultaneously, its energy density was increased to 54.2 Wh kg^-1 at 380.3 W kg^-1 after 64,000 cycles.

Uniform MnCo2O4.5 porous nanowires and quasi-cubes for hybrid supercapacitors with excellent electrochemical performances

In this work, uniform MnCo₂O_4.5 nanowires (NWs) on stainless steel foil (SSF) were prepared through a facile, cost-efficient, and eco-friendly hydrothermal method at 120 °C with a post-calcination process in air. The microstructure of MnCo₂O_4.5 samples could be tuned at different hydrothermal temperatures and quasi-cubes (QCs) were obtained in high yield at 150 °C. The MnCo₂O_4.5 NW powder peeled off from the SSF delivered an outstanding capacity of 248.62 C g^-1 at 1 A g^-1 with a capacity preservation of 179.43 C g^-1 at 8 A g^-1, while the QCs exhibited 177.19 and 111.73 C g^-1, respectively. To assess the possibility of its actual applications, a hybrid supercapacitor (HSC) device has been assembled by utilizing these MnCo₂O_4.5 NWs (QCs) and activated carbon (AC) as the cathode and anode, respectively. The MnCo₂O_4.5 NWs//AC HSC delivered a maximum capacity up to 116.95 C g^-1 and extraordinary cycling durability with only 3.56% capacity loss over 5000 cycles. Besides, the MnCo₂O_4.5 NWs//AC HSC achieved a maximum energy density of 25.41 W h kg^-1 at a power density of 782.08 W kg^-1, and for the QC-based HSC, it showed a lower energy density of 20.54 W h kg^-1 at 843.34 W kg^-1. These remarkable electrochemical properties demonstrate that the porous MnCo₂O_4.5 NWs and QCs may serve as promising cathodes for advanced hybrid supercapacitors with superior performance, and the present synthetic methodology may be applied to the preparation of other cobalt-based binary metal oxides with excellent electrochemical properties.