Selenizing CoMoO4 nanoparticles within electrospun carbon nanofibers towards enhanced sodium storage performance

Progress and Prospect of Bimetallic Oxides for Sodium-Ion Batteries: Synthesis, Mechanism, and Optimization Strategy

Sodium-ion batteries (SIBs) are considered as an alternative to and even replacement of lithium-ion batteries in the near future in order to address the energy crisis and scarcity of lithium resources due to the wide distribution and abundance of sodium resources on the earth. The exploration and development of high-performance anode materials are critical to the practical applications of advanced SIBs. Among various anode materials, bimetallic oxides (BMOs) have attracted special research attention because of their abundance, easy access, rich redox reactions, enhanced capacity and satisfactory cycling stability. Although many BMO anode materials have been reported as anode materials in SIBs, very limited studies summarized the progress and prospect of BMOs in practical applications of SIBs. In this review, recent progress and challenges of BMO anode materials for SIBs have been comprehensively summarized and discussed. First, the preparation methods and sodium storage mechanisms of BMOs are discussed. Then, the challenges, optimization strategies, and sodium storage performance of BMO anode materials have been reviewed and summarized. Finally, the prospects and future research directions of BMOs in SIBs have been proposed. This review aims to provide insight into the efficient design and optimization of BMO anode materials for high-performance SIBs.

Synthesis of CoMoO4 Nanofibers by Electrospinning as Efficient Electrocatalyst for Overall Water Splitting

To improve the traditional energy production and consumption of resources, the acceleration of the development of a clean and green assembly line is highly important. Hydrogen is considered one of the most ideal options. The method of production of hydrogen through water splitting constitutes the most attractive research. We synthesized CoMoO4 nanofibers by electrospinning along with post-heat treatment at different temperatures. CoMoO4 nanofibers show a superior activity for hydrogen evolution reaction (HER) and only demand an overpotential of 80 mV to achieve a current density of 10 mA cm-2. In particular, the CoMoO4 catalyst also delivers excellent performances of oxygen evolution reaction (OER) in 1 M KOH, which is a more complicated process that needs extra energy to launch. The CoMoO4 nanofibers also showed a superior stability in multiple CV cycles and maintained a catalytic activity for up to 80 h through chronopotentiometry tests. This is attributed mainly to a synergistic interaction between the different metallic elements that caused the activity of CoMoO4 beyond single oxides. This approach proved that bimetallic oxides are promising for energy production.

Phase structure engineering of MnCo2Ox within electrospun carbon nanofibers towards high-performance lithium-ion batteries

Metal oxides are prospective alternative anode materials to the commercial graphite for lithium ion batteries (LIBs), while their practical application is seriously hampered by their poor conductivities and large volume changes. Herein, we report the controllable synthesis of amorphous/crystalline MnCo₂O_x nanoparticles within porous carbon nanofibers (marked as MCO@CNFs) through a facile electrospinning strategy and subsequent annealing reactions. The phase structures from Co/MnO_X to amorphous MnCo₂O_x and crystalline MnCo₂O_4.5 can be readily tuned by thermal reduction/oxidation under controlled atmosphere and temperature. When examined as anode for LIBs, the optimized MCO@CNFs delivers a high stable capacity of 780.3 mA h g^-1 at 200 mA g^-1 after 250 cycles, which is attributed to the synergistic effect of the distinctive amorphous structure and defective carbon nanofiber matrices. Specifically, the amorphous structure with rich defects offers more reactive sites and multiple pathways for the Li⁺ diffusion, while carbon hybridization sufficiently improves the electrode conductivities as well as buffers the volume changes. More importantly, we demonstrate a convenient synthesis strategy to control the metal-to-oxide structure evolution within carbon matrices, which is of great importance in exploring high-performance electrodes for next generation LIBs.

A pre-oxidation strategy to improve architecture stability and electrochemical performance of Na2MnPO4F particles-embedded carbon nanofibers

The rational design of an excellent architecture for active materials combined with carbon matrix is of particular importanceto obtain flexible electrode material with high electrochemical properties. Well-designed nanofibers possess unique 3D network structure, which can significantly improve the electron/ion transportation and supplies sufficient active sites for Li⁺/Na⁺ insertion. Electrospinning-carbonization technology is a popular strategy to prepare nanofibers with active material embedded in carbon. It is found that the architecture of nanofibers tended to be wrecked and destroyed during the carbonization process without pre-oxidation treatment. In this study, we prepared Na₂MnPO₄F particles embedded in carbon nanofibers (Na₂MnPO₄F/C) using PVP as carbon source and investigated the strengthen mechanism of pre-oxidation on their architecture. The experiment and simulation results demonstrate that, without pre-oxidation, the main chain of PVP is severely ruptured during the carbonization procedure, consequently leads to fractured architecture of Na₂MnPO₄F/C nanofibers. In contrast, with pre-oxidation treatment, a long-chain and heat-resistance structured carbon matrix formed, and Na₂MnPO₄F/C nanofibers with stable architecture and improved electrochemical performance can be achieved. This study demonstrates a promising guide to construct carbon based nanofiber electrodes with stable architecture and high electrochemical performance.