Facile Synthesis of Manganese Cobalt Oxide/Nickel Cobalt Oxide Composites for High-Performance Supercapacitors

Hierarchical NiMn-LDH Hollow Spheres as a Promising Pseudocapacitive Electrode for Supercapacitor Application

Layered double hydroxides (LDH) are regarded as attractive pseudocapacitive materials due to their impressive capacitive qualities that may be adjustable to their morphological features. However, the layered structure of LDH renders them susceptible to structural aggregation, which inhibits effective electrolyte transport and limits their practical applicability after limited exposure to active areas. Herein, we propose a simple template-free strategy to synthesize hierarchical hollow sphere NiMn-LDH material with high surface area and exposed active as anode material for supercapacitor application. The template-free approach enables the natural nucleation of Ni-Mn ions resulting in thin sheets that self-assemble into a hollow sphere, offering expended interlayer spaces and abundant redox-active active sites. The optimal NiMn-LDH-12 achieved a specific capacitance of 1010.4 F g^-1 at a current density of 0.2 A g^-1 with capacitance retention of 70% at 5 A g^-1 after 5000 cycles with lower charge transfer impedance. When configured into an asymmetric supercapacitors (ASC) device as NiMn-LDH//AC, the material realized a specific capacitance of 192.4 F g^-1 at a current density of 0.2 A g^-1 with a good energy density of 47.9 Wh kg^-1 and a power density of 196.8 W kg^-1. The proposed morphological-tuning route is promising for designing template-free NiMn-LDHs spheres with practical pseudocapacitive characteristics.

Nanosheet-assembled porous MnCo2O4.5 microflowers as electrode material for hybrid supercapacitors and lithium-ion batteries

Herein, the MnCo₂O_4.5 microflowers (MFs) assembled by two-dimensional (2D) porous nanosheets were prepared through an initial solvothermal reaction with a subsequent annealing process. In this architecture, many interconnected 2D thin nanosheets were self-assembled together to form a 3D hierarchical MF with plenty of open channels. Such structure endows these MnCo₂O_4.5 MFs with large specific surface area of 156.85 m²/g for energy storage and provides rich ion diffusion pathways for ion transportation, thus the as-prepared MFs can exhibit good overall electrochemical performance in both hybrid supercapacitor (HSC) and lithium-ion battery (LIB). For the utilization in supercapacitor, the MFs deliver a specific capacity of 287.02 C/g at 1 A/g as well as a rate capability with 73.3 % capacity retention at 8 A/g. The energy density of the HSC assembled by MFs and activated carbon can reach up to 30.33 W h kg^-1 at 959.35 W kg^-1. When applied as the anode for Li-ion battery, a specific capacity of 1340.8 mA h g^-1 at 0.1 A/g and cycling performance with low capacity loss of 0.73 mAh/g per cycle after 200 cycles at 0.5 A/g can be achieved. This work uncovers a repeatable and facile synthetic strategy to prepare transition metal oxides with large specific surface area and good overall electrochemical property.

Controllable and Scale-Up Synthesis of Nickel-Cobalt Boride@Borate/RGO Nanoflakes via Reactive Impingement Mixing: A High-Performance Supercapacitor Electrode and Electrocatalyst

Large-scale synthesis of graphene-based nanomaterials in stirred tank reactor (STR) often results in serious agglomeration because of the poor control during micromixing process. In this work, reactive impingement mixing is conducted in a two-stage impinging jet microreactor (TS-IJMR) for the controllable and scale-up synthesis of nickel-cobalt boride@borate core-shell nanostructures on RGO flakes (NCBO/RGO). Benefiting from the good process control and improved micromixing efficiency of TS-IJMR, NCBO/RGO nanosheet provides a large BET surface area, abundant of suitable mesopores (2–5 nm), fast ion diffusion, and facile electron transfer within the whole electrode. Therefore, NCBO/RGO electrode exhibits a high specific capacitance of 2383 F g−1 at 1 A g−1, and still retains 1650 F g−1 when the current density is increased to 20 A g−1, much higher than those of nickel boride@borate/RGO (NBO/RGO) and cobalt boride@borate/RGO (CBO/RGO) synthesized in TS-IJMR, as well as NCBO/RGO-S synthesized in STR. In addition, an asymmetric supercapacitor (NCBO/RGO//AC) is constructed with NCBO/RGO and activated carbon (AC), which displays a high energy density of 53.3 W h kg−1 and long cyclic lifespan with 91.8% capacitance retention after 5000 charge-discharge cycles. Finally, NCBO/RGO is used as OER electrocatalyst to possess a low overpotential of 309 mV at a current density of 10 mA cm−2 and delivers a good long-term durability for 10 h. This study opens up the potential of controllable and scale-up synthesis of NCBO/RGO nanosheets for high-performance supercapacitor electrode materials and OER catalysts.

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.

Zn induced NiCo composites modified by carbon materials as a battery-type electrode material for high-performance supercapacitors

The development of simple preparation and excellent capacity performance electrode materials is the key to energy conversion and storage for supercapacitors. Based on the growth mechanism of crystal, Zn induced NiCo nanosheets and nanoneedles composite structure deposed on Ni foam (ZNC) are successfully attained by a facile one-step method, the growth mechanism of the composite structure is further discussed. Because of its unique composites structure and additional modification of carbon, the carbon modified ZNC (ZNC@C) delivers better energy storage ability (2280 mC cm^-2at 2 mA cm^-2) compare to ZNC. An asymmetric supercapacitor (ASC) is assembled by ZNC@C as the positive electrode and carbonized popcorn as the negative electrode. The ASC exhibits good energy storage performance. Zn also positively affects the adsorption energy to enhance the capacitance property based on Density Functional theory calculation. The simple method for the composite structure by tuning the kinetics behaver of the crystal can provide a new strategy in synthesizing the materials, and the material with a unique structure and high performance will have potential applications in the field of energy storage.

In situ synthesis of oxidized MXene-based metal cobalt spinel nanocomposites for an excellent promotion in thermal decomposition of ammonium perchlorate

Oxidized MXene-supported MCo2O4 (oxidized MXene/MCo2O4, M = Mn, Zn, Cu and Co) nanocomposites with an excellent catalytic performance for AP decomposition were successfully synthesized through a facile hydrothermal assisted calcination method.

Preparation of mesoporous CoNiO2 hexagonal nanoparticles for asymmetric supercapacitors via a hydrothermal microwave carbon bath process

Mesoporous CoNiO₂ hexagonal nanoparticles prepared via a hydrothermal microwave carbon bath process instead of the conventional calcination method have excellent pseudocapacitance properties.