Influence of nickel doping on MnO2 nanoflowers as electrocatalyst for oxygen reduction reaction

Activation of MnO6 Units via an Interfacial Electric Field: Electron Injection into Mn t2g for Rapid and Stable Sodium Ion Storage in CeO2/MnOx

Manganese-based oxides (MnOx) suffer from sluggish charge diffusion kinetics and poor cycling stability in sodium ion storage. Herein, an interfacial electric field (IEF) in CeO2/MnOx is constructed to obtain high electronic/ionic conductivity and structural stability of MnOx. The as-designed CeO2/MnOx exhibits a remarkable capacity of 397 F g-1 and favorable cyclic stability with 92.13% capacity retention after 10,000 cycles. Soft X-ray absorption spectroscopy and partial density of states results reveal that the electrons are substantially injected into the Mn t2g orbitals driven by the formed IEF. Correspondingly, the MnO6 units in MnOx are effectively activated, endowing the CeO2/MnOx with fast charge transfer kinetics and high sodium ion storage capacity. Moreover, In situRaman verifies a remarkably increased structural stability of CeO2/MnOx, which is attributed to the enhanced Mn─O bond strength and efficiently stabilized MnO6 units. Mechanism studies show that the downshift of Mn 3d-band center dramatically increases the Mn 3d-O 2p orbitals overlap, thus inhibiting the Jahn-Teller (J-T) distortion of MnOx during sodium ion insertion/extraction. This work develops an advanced strategy to achieve both fast and sustainable sodium ion storage in metal oxides-based energy materials.

Engineering of Co3O4 electrode via Ni and Cu-doping for supercapacitor application

Although cobalt oxides show great promise as supercapacitor electrode materials, their slow kinetics and low conductivity make them unsuitable for widespread application. We developed Ni and Cu-doped Co3O4 nanoparticles (NPs) via a simple chemical co-precipitation method without the aid of a surfactant. The samples were analyzed for their composition, function group, band gap, structure/morphology, thermal property, surface area and electrochemical property using X-ray diffraction (XRD), ICP-OES, Fourier transform infrared (FTIR) spectroscopy, Ultraviolet-visible (UV-Vis), Scanning electron microscopy (SEM), Thermogravimetric analysis (TGA) and/or Differential thermal analysis (DTA), Brunauer-Emmett-Teller (BET), and Impedance Spectroscopy (EIS), Cyclic voltammetry (CV), respectively. Notably, for the prepared sample, the addition of Cu to Co3O4 NPs results in a 11.5-fold increase in specific surface area (573.78 m2 g-1) and a decrease in charge transfer resistance. As a result, the Ni doped Co3O4 electrode exhibits a high specific capacitance of 749 F g-1, 1.75 times greater than the pristine Co3O4 electrode's 426 F g-1. The electrode's enhanced surface area and electronic conductivity are credited with the significant improvement in electrochemical performance. The produced Ni doped Co3O4 electrode has the potential to be employed in supercapacitor systems, as the obtained findings amply demonstrated.

Enhancing pseudocapacitive properties of cobalt oxide hierarchical nanostructures via iron doping

Through co-precipitation and post-heat processing, nanostructured Fe-doped Co₃O₄ nanoparticles (NPs) were developed. Using the SEM, XRD, BET, FTIR, TGA/DTA, UV-Vis, and techniques were examined. The XRD analysis presented that Co₃O₄ and Co₃O₄ nanoparticles that had been doped with 0.25 M Fe formed single cubic phase Co₃O₄ NPs with average crystallite sizes of 19.37 nm and 14.09 nm, respectively. The as prepared NPs have porous architectures via SEM analyses. The BET surface areas of Co₃O₄ and 0.25 M Fe-doped Co₃O₄ NPs were 53.06 m²/g and 351.56 m²/g, respectively. Co₃O₄ NPs have a band gap energy of 2.96 eV and an extra sub-band gap energy of 1.95 eV. Fe-doped Co₃O₄ NPs were also found to have band gap energies between 2.54 and 1.46 eV. FTIR spectroscopy was used to determine whether M-O bonds (M = Co, Fe) were present. The doping impact of iron results in the doped Co₃O₄ samples having better thermal characteristics. The highest specific capacitance was achieved using 0.25 M Fe-doped Co₃O₄ NPs at 5 mV/s, which corresponding to 588.5 F/g via CV analysis. Additionally, 0.25 M Fe-doped Co₃O₄ NPs had energy and power densities of 9.17 W h/kg and 472.1 W/kg, correspondingly.

Ag doped Co3O4 nanoparticles for high-performance supercapacitor application

Ag doped Co₃O₄ nanoparticles (NPs) were synthesized via a co-precipitation method changing the concentration of Ag. The crystal structure, morphology, surface area, functional group, optical band gap, and thermal property were investigated by XRD, SEM, BET, FTIR, UV-Vis, and TGA/DTA techniques. The XRD results showed the formation of single-cubic Co₃O₄ nanostructured materials with an average crystal size of 19.37 nm and 12.98 nm for pristine Co₃O₄ and 0.25 M Ag-doped Co₃O₄ NPs. Morphological studies showed that pristine Co₃O₄ and 0.25 M Ag-doped Co₃O₄ NPs having a porous structure with small spherical grains, porous structures with sponge-like structures, and loosely packed porous structures, respectively. The pristine and 0.25 M Ag-doped Co₃O₄ NPs showed BET surface areas of 53.06 m²/g, and 407.33 m²/g, respectively. The band gap energy of Co₃O₄ NPs were 2.96 eV, with additional sub-bandgap energy of 1.95 eV. Additionally, it was discovered that the band gap energies of 0.25 M Ag-doped Co₃O₄ NPs ranged from 2.2 to 2.75 eV, with an extra sub-band with energies ranging from 1.43 to 1.94 eV for all as-prepared samples. The Ag-doped Co₃O₄ as prepared samples show improved thermal properties due to the doping effect of silver. The CV test confirmed that the 0.25 M Ag-doped Co₃O₄ NPs exhibited the highest specific capacitance value of 992.7 F/g at 5 mV/s in a 0.1 M KOH electrolyte solution. The energy density and power density of 0.25 M Ag-doped Co₃O₄ NPs were 27.9 W h/kg and 3816.1 W/kg, respectively.

Engineering nanostructured Ag doped α-MnO2 electrocatalyst for highly efficient rechargeable zinc-air batteries

Engineering of highly active, and non-precious electrocatalysts are vital to enhance the air-electrodes of rechargeable zinc-air batteries (ZABs). We report a facile co-precipitation technique to develop Ag doped α-MnO₂ nanoparticles (NPs) and investigate their application as cathode materials for ZABs. The electrochemical and physical characteristics of α-MnO₂ and Ag doped α-MnO₂ NPs were compared and examined via CP, CV, TGA/DTA, FT-IR, EIS, and XRD analysis. CV result displayed higher potential and current for ORR in Ag doped α-MnO₂ NPs than α-MnO₂; but, ORR performance decreased when the Ag doping was raised from 7.5 to10 mmol. Moreover, α-MnO₂ and Ag doped α-MnO₂ NPs showed 2.1 and 3.8 electron transfer pathway, respectively, showing Ag doped α-MnO₂ performance to act as an active ORR electrocatalyst for ZABs. The EIS investigation exhibited that charge-transfer resistance for Ag doped α-MnO₂ was extremely lower associated to the MnO₂ demonstrating that the successful loading of Ag in α-MnO₂. A homemade ZAB based on Ag–MnO₂-7.5 showed a high open circuit potential, low ohmic resistances, and excellent discharge profile at a constant current density of 1 mA/g. Moreover, Ag–MnO₂-7.5 show a specific capacity of 795 mA h g⁻¹ with corresponding high energy density ∼875 Wh kg⁻¹ at 1 mA cm⁻² discharging conditions.

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Ag doped α-MnO₂ electrode for rechargeable zinc–air battery was prepared via a facile co-precipitation technique.

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Ag doped α-MnO₂ electrode shows lower charge transfer resistance associated to un-doped MnO₂ electrode.

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Ag doped α-MnO₂ shows enhanced ORR kinetics in oxygen electrode potential.

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The capacitance performance of Ag doped α-MnO₂ electrodes was highly improved.

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Ag doped α-MnO₂ electrode showed energy density of 69.3 W h kg−1 and power density of 722.9 W kg−1.

Engineering techniques to dendrite free Zinc-based rechargeable batteries

Rechargeable Zn-based batteries (RZBs) have garnered a great interest and are thought to be among the most promising options for next-generation energy storage technologies due to their low price, high levels of safety, adequate energy density and environmental friendliness. However, dendrite formation during stripping/plating prevents rechargeable zinc-based batteries from being used in real-world applications. Dendrite formation is still a concern, despite the fact that inhibitory strategies have been put up recently to eliminate the harmful effects of zinc dendrites. Thus, in order to direct the strategies for inhibiting zinc dendrite growth, it is vital to understand the formation mechanism of zinc dendrites. Hence, for the practical application of zinc-based batteries, is essential to use techniques that effectively prevent the creation and growth of zinc dendrites. The development and growth principles of zinc dendrites are first made clear in this review. The recent advances of solutions to the zinc dendrite problem are then discussed, including strategies to prevent dendrite growth and subsequent creation as much as possible, reduce the negative impacts of dendrites, and create dendrite-free deposition processes. Finally, the challenges and perspective for the development of zinc-based batteries are discussed.

Engineering Co3O4/MnO2 nanocomposite materials for oxygen reduction electrocatalysis

Stable and active electrocatalysts preparation for the oxygen reduction reaction (ORR) is essential for an energy storage and conversion materials (e.g. metal-air batteries). Herein, we prepared a highly-active MnO₂ and Co₃O₄/MnO₂ nanocomposite electrocatalysts using a facial co-precipitation approach. The electrocatalytic activity was examined in alkaline media with LSV and CV. Additionally, the physicochemical characteristics of the MnO₂ and Co₃O₄/MnO₂ composite materials were studied via SEM, XRD, BET, UV-Vis, TGA/DTA, ICP-OES and FTIR. Morphological studies indicated that a pure MnO₂ has a spherical flower-like architecture, whereas Co₃O₄/MnO₂ nanocomposites have an aggregated needle-like structure. Moreover, from the XRD investigation parameters such as the dislocation density, micro-strain, and crystallite size were analyzed. The calculated energy bandgaps for the MnO₂, Co₃O₄/MnO₂-1-5, and Co₃O₄/MnO₂-1-1 nanocomposites were 3.07, 2.6, and 2.3 eV, correspondingly. The FTIR spectroscopy was also employed to study the presence of M-O bonds (M = Mn, Co). The thermal gravimetric investigation showed that the Co₃O₄/MnO₂ nanocomposite materials exhibited improved thermal stability, confirming an enhanced catalytic activity of ORR for MnO₂/Co₃O₄-1-1 composite materials for ORR. These results confirm that the prepared Co₃O₄/MnO₂ composite materials are promising air electrode candidates for the energy storage and conversion technologies.