Porous MnCo2O4 as superior anode material over MnCo2O4 nanoparticles for rechargeable lithium ion batteries

Smart Textile Flexible MnCo2O4 Electrodes: Urea Surface Modification for Improved Electrochemical Functionality

Surface microstructure modification of metal oxides also improves the electrochemical performance of metal oxide nanoparticles. The present investigation demonstrates how varying the urea molar content during the hydrothermal process altered the surfaces of MnCo2O4 nanoparticles. Successive increases of 0.1 M in urea concentration transformed the surface shape of MnCo2O4 nanoparticles from flower-like to sheet-like microstructures. Excellent electrochemical performance of MnCo2O4 nanoparticles was demonstrated in an aqueous 1 M KOH electrolyte. The improved MnCo2O4 nanoparticles have been employed to develop an asymmetric supercapacitor (ASC). The ASC device exhibits an energy density of 13 Wh/kg at a power density of 553 W/kg and a specific capacitance of 29 F g-1 at a current density of 4 mA/cm2. The MnCo2O4 nanoparticle electrode demonstrates remarkable electrocatalytic activity in both HER and OER. The MnCo2O4 electrode shows overpotential for HER and OER at 356 mV and 1.46 V, respectively. The Tafel slopes for HER and OER of the MnCo2O4 electrode are 356 mV/dec and 187 mV/dec, respectively.

Boosting the high-rate performance of lithium-ion battery anodes using MnCo2O4/Co3O4 nanocomposite interfaces

Herein, a mesoporous MnCo2O4/Co3O4 nanocomposite was fabricated using a polyvinylpyrrolidone (PVP)-assisted hydrothermal synthesis method by maintaining only the non-stoichiometric ratio of Mn and Co (2 : 6), leading to an extra phase of Co3O4 coupled with MnCo2O4. Microstructural analysis showed that the obtained sample has a uniform nanowire-like morphology composed of interconnected nanoparticles. The stoichiometric ratio (2 : 4) was maintained to synthesize pure MnCo2O4 for comparative analysis. However, the obtained structure of pure MnCo2O4 was found to be irregular and fragile. After their employment as anode-active materials, the nanocomposite electrode showed superior high rate capability (1043.8 mA h g-1 at 5C) and long-term cycling stability (773.6 mA h g-1 after 500 cycles at 0.5C) in comparison to the pure MnCo2O4 electrode (771.5 mA h g-1 at 5C and 638.9 mA h g-1 at 0.5C after 500 cycles). It was believed that the extra phase of Co3O4 may also participate in the electrochemical reactions due to its high electrochemically active nature. Benefiting from the appealing architectural features and striking synergistic effect, the integrated MnCo2O4/Co3O4 nanocomposite anode exhibits excellent electrochemical properties and high cycle stability for LIBs.

β-Cyclodextrin-Stabilized CuO/MXene Nanocomposite as an Electrode Material for High-Performance Supercapacitors

Supercapacitors are the best energy storage systems due to their high power density, quick charge/discharge rate, and long-term reliability. In this study, β-cyclodextrin-stabilized CuO nanoparticles (CuO@βCD NPs) were synthesized through a simple reduction method and anchored on the surface of MXene nanosheets in three different proportions (1:1, 4:1, and 1:4) to obtain CuO@βCD/MXene nanocomposites through the wet-impregnation method. The formation of CuO@βCD NPs and their physicochemical characteristics were verified by XRD, XPS, FE-SEM, and HR-TEM analysis. The actual focus is on the evaluation of the electrochemical performances of CuO@βCD, MXene, and CuO@βCD/MXene nanocomposites for supercapacitor applications. The cyclic voltammetry and galvanostatic charge-discharge analysis revealed the pseudocapacitance and an improved specific capacitance of 1693.43 F g-1 at 0.90 A g-1 for the CuO@βCD/MXene (1:1) nanocomposite. The electrochemical impedance analysis displays superior electrical conductivity with a low charge transfer resistance value on incorporating CuO@βCD between the MXene layers. Furthermore, the CuO@βCD/MXene (1:1) nanocomposite exhibited improved long-term cycling stability by retaining 86% of its initial specific capacitance even after the 10,000th cycle at the current density of 4.54 A g-1. Based on the electrochemical performance, the CuO@βCD/MXene (1:1) nanocomposite proves its suitability as an electrode material for supercapacitor application with long-term cycling stability and rate capability.

An Electrically Rechargeable Zinc/Air Cell with an Aqueous Choline Acetate Electrolyte

Due to the feasibility of an electrically rechargeable zinc/air cell made of a zinc foil as active material, an aqueous choline acetate (ChAcO) mixture as an electrolyte and a spinel MnCo₂O₄ (MCO) and NiCo₂O₄ (NCO) as a bi-functional oxygen catalyst was investigated in this work. The 30 wt.% water-containing aqueous ChAcO solution showed high contact angles close to those of KOH favoring triple-phase boundary formation in the gas diffusion electrode. Conductivity and pH value of 30 wt.% H₂O/ChAcO amounted to 5.9 mS cm⁻¹ and 10.8, respectively. Best results in terms of reversible capacity and longevity of zinc/air cell were yielded during 100 h charge/discharge with the MnCo₂O₄ (MCO) air electrode polarization procedure at 100 µA cm⁻² (2.8 mA g⁻¹_zinc). The corresponding reversible capacity amounted to 25.4 mAh (28% depth of discharge (DOD)) and the energy efficiency ranged from 29–54% during the first and seventh cycle within a 1500 h polarization period. Maximum active material utilization of zinc foil at 100 µA cm⁻² was determined to 38.1 mAh (42% DOD) whereas a further charging step was not possible due to irreversible passivation of the zinc foil surface. A special side-by-side optical cell was used to identify reaction products of the zinc/air system during a single discharge step in aqueous ChAcO that were identified as Zn(OH)₂ and ZnO by Raman analysis while no carbonate was detected.

The lithium ions storage behavior of heteroatom-mediated echinus-like porous carbon spheres: From co-doping to multi-atom doping

This study proposed a facile method to prepare echinus-like porous carbon spheres (PCS) with different heteroatom doping for lithium ions battery (LIBs). A metal-organophosphine framework (MOPF) was synthesized by employing riboflavin sodium phosphate as an organic ligand to conjugate with metal ions and then carbonized at mild temperature, leading to the formation of heteroatom doped PCS (H-PCS). As a result, (N, P) co-, (N, P, Ni) tri-, (N, P, Co) tri- and (N, Ni, Co, P) tetra-doped PCS were obtained to examine the insight into lithium-ion storage behavior of H-PCS. It was found that the specific surface area, pore texture and structural defects of H-PCS were dependent on doping of heteroatoms as well as the charge transfer resistance and Li-ion diffusion coefficient. Significantly, the redox reaction potential during the charge/discharge could be mediated upon the doping. Thus, when evaluated as anode for LIBs, the (N, Ni, Co, P) tetra-doped PCS exhibited highly reversible capacity of 680 mAh g^-1 at 0.1 A g^-1, excellent rate capability (115.9 mAh g^-1 at 1.0 A g^-1) and superior cycling performance (399.6 mAh g^-1 at 0.1 A g^-1). Moreover, the cyclic voltammogram measurements demonstrated that the doping of metal atoms was favorable for improving the capacitive contribution of surface limited diffusion. Thus, this work highlighted the importance of HCP with defined doping which could be considered as one of the prominent candidates for high-performance LIBs' anode.

Hierarchical porous MnCo2O4 yolk-shell microspheres from MOFs as secondary nanomaterials for high power lithium ion batteries

Hierarchical porous MnCo2O4 yolk-shell microspheres have been synthesized via a facile chemical precipitation method with subsequent calcination treatment. The hierarchical porous MnCo2O4 yolk-shell microspheres as secondary nanomaterials can improve the effective contact area between the MnCo2O4 electrode and electrolyte, accommodate the volume variations during cycling, and shorten the Li+ diffusion path in the nanoparticles. Benefiting from their particular structure and interconnected pores, as anodes for lithium ion batteries, the hierarchical porous MnCo2O4 yolk-shell microspheres show high reversible lithium storage capacity, excellent cycling performance and enhanced rate capability. More importantly, they also exhibit long-life and high-rate lithium storage as high as 691.3 mA h g-1 after 500 cycles even at 1 C.