Facile Self-Assembly Route to Co3O4 Nanoparticles Confined into Single-Walled Carbon Nanotube Matrix for Highly Reversible Lithium Storage

Recent Advances on Heterojunction-Type Anode Materials for Lithium-/Sodium-Ion Batteries

Rechargeable batteries are key in the field of electrochemical energy storage, and the development of advanced electrode materials is essential to meet the increasing demand of electrochemical energy storage devices with higher density of energy and power. Anode materials are the key components of batteries. However, the anode materials still suffer from several challenges such as low rate capability and poor cycling stability, limiting the development of high-energy and high-power batteries. In recent years, heterojunctions have received increasing attention from researchers as an emerging material, because the constructed heterostructures can significantly improve the rate capability and cycling stability of the materials. Although many research progress has been made in this field, it still lacks review articles that summarize this field in detail. Herein, this review presents the recent research progress of heterojunction-type anode materials, focusing on the application of various types of heterojunctions in lithium/sodium-ion batteries. Finally, the heterojunctions introduced in this review are summarized, and their future development is anticipated.

Effect of Co3O4 Nanoparticles on Improving Catalytic Behavior of Pd/Co3O4@MWCNT Composites for Cathodes in Direct Urea Fuel Cells

Direct urea fuel cells (DUFCs) have recently drawn increased attention as sustainable power generation devices because of their considerable advantages. Nonetheless, the kinetics of the oxidation-reduction reaction, particularly the electrochemical oxidation and oxygen reduction reaction (ORR), in direct urea fuel cells are slow and hence considered to be inefficient. To overcome these disadvantages in DUFCs, Pd nanoparticles loaded onto Co₃O₄ supported by multi-walled carbon nanotubes (Pd/Co₃O₄@MWCNT) were employed as a promising cathode catalyst for enhancing the electrocatalytic activity and oxygen reduction reaction at the cathode in DUFCs. Co₃O₄@MWCNT and Pd/Co₃O₄@MWCNT were synthesized via a facile two-step hydrothermal process. A Pd/MWCNT catalyst was also prepared and evaluated to study the effect of Co₃O₄ on the performance of the Pd/Co₃O₄@MWCNT catalyst. A current density of 13.963 mA cm^-2 and a maximum power density of 2.792 mW cm^-2 at 20 °C were obtained. Pd/Co₃O₄@MWCNT is a prospectively effective cathode catalyst for DUFCs. The dilution of Pd with non-precious metal oxides in adequate amounts is economically conducive to highly practical catalysts with promising electrocatalytic activity in fuel cell applications.

Co3O4 hollow nanospheres/carbon-assembled mesoporous polyhedron with internal bubbles encapsulating TiO2 nanosphere for high-performance lithium ion batteries

Co₃O₄ hollow nanospheres 15 nm in the diameter were assembled to the mesoporous polyhedron together with carbon. Within the Co₃O₄ polyhedrons, the bubbles 300-500 nm in diameter were uniformly generated. Every bubble further encapsulated one TiO₂ nanosphere, forming a unique sphere-bubble structure. The specific surface area and the pore volume were calculated to be 97.85 and 0.31 cm³ g^-1. When evaluated as anode material for lithium ion batteries, the as-prepared material exhibited superior lithium storage properties with high specific capacity, excellent cycling stability and good rate capability. After 400 cycles, the discharge capacity of 609 mAh g^-1 was still delivered at current density of 335 mA g^-1. Even at a high current density of 2000 mA g^-1, the reversible capacity reached 296 mAh g^-1. The outstanding electrochemical performance was attributed to the unique hybrid structure, which avoids nanomaterial aggregation, promotes ion diffusion and electron transfer, accommodates volume change of Co₃O₄ during (de)lithiation process, enhances structure strength, cycling stability and space utilization ratio of the hollow material.

Aggregation-Morphology-Dependent Electrochemical Performance of Co3O4 Anode Materials for Lithium-Ion Batteries

The aggregation morphology of anode materials plays a vital role in achieving high performance lithium-ion batteries. Herein, Co₃O₄ anode materials with different aggregation morphologies were successfully prepared by modulating the morphology of precursors with different cobalt sources by the mild coprecipitation method. The fabricated Co₃O₄ can be flower-like, spherical, irregular, and urchin-like. Detailed investigation on the electrochemical performance demonstrated that flower-like Co₃O₄ consisting of nanorods exhibited superior performance. The reversible capacity maintained 910.7 mAh·g⁻¹ at 500 mA·g⁻¹ and 717 mAh·g⁻¹ at 1000 mA·g⁻¹ after 500 cycles. The cyclic stability was greatly enhanced, with a capacity retention rate of 92.7% at 500 mA·g⁻¹ and 78.27% at 1000 mA·g⁻¹ after 500 cycles. Electrochemical performance in long-term storage and high temperature conditions was still excellent. The unique aggregation morphology of flower-like Co₃O₄ yielded a reduction of charge-transfer resistance and stabilization of electrode structure compared with other aggregation morphologies.

Flexible and Wearable All-Solid-State Al-Air Battery Based on Iron Carbide Encapsulated in Electrospun Porous Carbon Nanofibers

In this work, electrospinning N-doped carbon nanofibers containing iron carbide (Fe₃C@N-CFs) are synthesized and employed as the cathode in the flexible Al-air battery. Benefiting from the excellent catalytic activity of the iron carbide which is uniformly encapsulated in the N-doped carbon matrix, as well as the large specific surface area of the cross-linked network nanostructure, the as-prepared Fe₃C@N-CFs show outstanding catalytic activity and stability toward oxygen reduction reaction. The as-fabricated all-solid-state Al-air batteries with Fe₃C@N-CF catalyst show a stable discharge voltage (1.61 V) for 8 h, giving a capacity of 1287.3 mA h g^-1.

Preparation of 3D hierarchical porous Co3O4 nanostructures with enhanced performance in lithium-ion batteries

Three-dimensional hierarchical Co₃O₄ microspheres assembled by well-aligned 1D porous nanorods were successfully fabricated. The sample exhibited excellent electrochemical properties as anode materials for LIBs.

Two-dimensional porous Co3O4nanosheets for high-performance lithium ion batteries

2D porous Co₃O₄nanosheets are synthesizedviaa self-sacrificing template method. When applied as an anode for LIBs, the as-obtained 2D porous Co₃O₄nanosheets exhibit a high discharge specific capacity, good cycling stability, and high rate capability.