Sacrificial Template Strategy toward a Hollow LiNi1/3Co1/3Mn1/3O2 Nanosphere Cathode for Advanced Lithium-Ion Batteries

Spinel structure of activated carbon supported MFe2O4 composites as an economic and efficient electrocatalyst for oxygen reduction reaction in neutral media

For more sustainability and marketing of microbial fuel cells (MFCs) in wastewater treatment, the sluggish kinetics of cathode oxygen reduction reaction (ORR) and platinum scarcity (with its high cost) should be swept away. So, this work aimed to synthesize metal ferrite (MFe2O4; M = Mn, Cu, and Ni) -based activated carbon composites as inexpensive ORR cathode catalysts. The composites were synthesized using a facile modified co-precipitation approach with low-thermal treatment and labeled as MnFe2O4/AC, CuFe2O4/AC, and NiFe2O4/AC. The as-synthesized catalysts are physicochemically characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared microscopy (FTIR), Barrett-Joyner-Halenda (BJH), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and electron spin resonance (ESR). The electrochemical catalytic performance toward ORR was studied in a phosphate buffer solution (PBS) at neutral media via cyclic voltammetry (CV) and linear sweep voltammetry (LSV). MnFe2O4/AC has the highest onset potential (Eonset) value of − 0.223 V compared to CuFe2O4/AC (− 0.280 V) and NiFe2O4/AC (− 0.270 V). MnFe2O4/AC also has the highest kinetic current density (jK) and lowest Tafel slope (− 5 mA cm−2 and − 330 mV dec−1) compared to CuFe2O4/AC (− 3.05 mA cm−2 and − 577 mV dec−1) and NiFe2O4/AC (− 2.67 mA cm−2 and − 414 mV dec−1). The ORR catalyzed by MnFe2O4/AC at pH = 7 proceeds via a 4e− -kinetic pathway. The ESR is in good agreement with the electrochemical analysis due to the highest ∆Hppvalue for MnFe2O4/AC compared to CuFe2O4/AC and NiFe2O4/AC. Thus, MnFe2O4/AC is suggested as a promising alternative to Pt- electrocatalyst cathode for MFCs at neutral conditions.

Graphical Abstract

Hollow structured cathode materials for rechargeable batteries

Hollow structuring has been intensively studied as an effective strategy to improve the electrochemical performance of the electrode materials for rechargeable batteries in terms of specific capacity, rate capability, and cycling performance. To date, hollow structured anode materials have been extensively investigated, while hollow structured cathode materials (HSCMs) are relatively less explored because of the difficulties in morphological control as well as the concern of reduced volumetric capacities. In this paper, we provide an overview of the research advances in the synthesis and evolution of HSCMs for metal (Li, Na, etc.) ion batteries. Attributing to the advantages of hollow structures including high surface area, excellent accessibility to active sites, and enhanced mass transport and diffusion, hollow structuring can significantly improve the performance of high-capacity cathode materials with low kinetics, such as lithium rich layered oxides, silicates, and V₂O₅. It is anticipated that the precise and facile control of the spatial configuration can balance the electrochemical performance of HSCMs and the volumetric capacities of HSCMs, leading to practical high-performance batteries.

Architectural Design of Self-Assembled Hollow Superstructures

Colloidal nanoparticle assemblies are widely designed and fabricated via various building blocks to enhance their intrinsic properties and potential applications. Self-assembled hollow superstructures have been a focal point in nanotechnology for several decades and are likely to remain so for the foreseeable future. The novel properties of self-assembled hollow superstructures stem from their effective spatial utilization. As such, a comprehensive appreciation of the interactive forces at play among individual building blocks is a prerequisite for designing and managing the self-assembly process, toward the fabrication of optimal hollow nanoproducts. Herein, the emerging approaches to the fabrication of self-assembled hollow superstructures, including hard-templated, soft-templated, self-templated, and template-free methods, are classified and discussed. The corresponding reinforcement mechanisms, such as strong ligand interaction strategies and extra-capping strategies, are discussed in detail. Finally, possible future directions for the construction of multifunctional hollow superstructures with highly efficient catalytic reaction systems and an integration platform for bioapplications are discussed.

Morphology-Controlled One-Step Synthesis of Nanostructured LiNi1/3Mn1/3Co1/3O2 Electrodes for Li-Ion Batteries

Nanostructured electrodes effectively enhance the kinetics of the charge/discharge process in lithium-ion (Li-ion) batteries. However, the fabrication of these electrodes often involves complex processing steps. This study demonstrates a one-step improved flame spray pyrolysis synthesis approach to directly deposit the most common Li-ion battery cathode material LiNi_1/3Mn_1/3Co_1/3O₂ onto current collectors, which is identified as reactive spray deposition technology (RSDT). Because of the economical and continuous nature of RSDT, the industrial scale of manufacturing nanostructured electrodes for Li-ion batteries can be potentially developed. Morphologies of the electrodes are well controlled so that their electrochemical properties can be tailored to accommodate intended applications. In detail, by adjusting the precursor concentration in the solution feed during the operation of RSDT, the specific surface area of synthesized material can be fine-tuned accordingly. Although the electrodes prepared with low precursor concentration exhibit the highest surface area and deliver the highest initial discharge capacity of 192.1 mAh g^-1, the most stable cycling performance is demonstrated by the electrodes fabricated with high precursor concentration, retaining 93.6% of the initial capacity after 100 cycles in half-cell testing. This innovative direct deposition method considerably simplifies the manufacture process of high-performance nanostructured electrodes and enables effortless modification of their properties. Moreover, no hazardous waste is generated from this synthesis route.