Manipulating the Electronic Structure of Graphite Intercalation Compounds for Boosting the Bifunctional Oxygen Catalytic Performance

Fe3O4-modified FeCl3/graphite intercalation compound confinement architecture for unleashing the high-performance anode potential of lithium-ion batteries

The ferric trichloride (FeCl3)-intercalated graphite intercalation compound (GIC) has high reversible capacity and bulk density, making it a promising anode material for lithium ion batteries. However, its practical application has been limited by the poor cycle performance due to chloride dissolution and shuttling issues. Herein, FeCl3-GIC is used as the precursor material to synthesize a nano-Fe3O4-modified intercalation material by a solvothermal method. The Fe3O4 moiety at the edge of FeCl3-GIC provides a robust chemical anchoring effect on the chlorides. Together with the two-dimensional graphite layer, it forms a confinement space, which effectively immobilizes soluble chlorides. Attributed to the distinctive structural design, the Fe3O4-FeCl3/GIC 25% C electrode offers a high reversible capacity of 691.4 mA h g-1 at 1000 mA g-1 after 400 cycles. At 2000 and 5000 mA g-1, the reversible specific capacity of the Fe3O4-FeCl3/GIC 25% C electrode is 345.6 and 218.3 mA h g-1, respectively. This work presents an innovative method to improve the lifespan of GIC.

FeNiCo|MnGaOx Heterostructure Nanoparticles as Bifunctional Electrocatalyst for Zn-Air Batteries

Driven by the pressing demand for stable energy systems, zinc-air batteries (ZABs) have emerged as crucial energy storage solutions. However, the quest for cost-effective catalysts to enhance vital oxygen evolution and reduction reactions remains challenging. FeNiCo|MnGaOx heterostructure nanoparticles on carbon nanotubes (CNTs) are synthesized using liquid-phase reduction and H2 calcination approach. Compared to its component, such FeNiCo|MnGaOx/CNT shows a high synergistic effect, low impedance, and modulated electronic structure, leading to a superior bifunctional catalytic performance with an overpotential of 255 mV at 10 mA cm-2 and half-wave potential of 0.824 V (ω = 1600 rpm and 0.1 m KOH electrolyte). Moreover, ZABs based on FeNiCo|MnGaOx/CNT demonstrate notable features, including a peak power density of 136.1 mW cm-2, a high specific capacity of 808.3 mAh gZn -1, and outstanding stability throughout >158 h of uninterrupted charge-discharge cycling. Theoretical calculations reveal that the non-homogeneous interface can introduce more carriers and altered electronic structures to refine intermediate adsorption reactions, especially promoting O* formation, thereby enhancing electrocatalytic performance. This work demonstrates the importance of heterostructure interfacial modulation of electronic structure and enhancement of adsorption capacity in promoting the implementation of OER/ORR, ZABs, and related applications.

Intervention-Free Graphitization of Carbon Microspheres from a Non-Graphitizing Polymer at Low Temperature: Nanopores as Dynamic Nanoreactors

Graphitizability of organic precursors is the topic of numerous investigations due to the wide applications of graphitic materials in the industry and emerging technologies of supercapacitors, batteries, etc. Most polymers, such as polydivinyl benzene (PDVB) are classified as non-graphitizings that do not convert to Graphite even after heating to 3000℃. Here, for the first time, the development of graphitic structure in the hierarchal porous sulfonated-PDVB microspheres without employing specific equipment or additives like metal catalysts, organic ingredients, or graphite particles, at 1100°C is reported. The abnormal additive-free graphitic structure formation is confirmed by Raman spectroscopy (ID/IG = 0.87), high-resolution transmission electron microscopy (HRTEM), and selected area diffraction patterns (SAED), as well as x-ray diffraction patterns (XRD), while preservation of aromatic compounds from the carbonization is detected by Fourier transform infrared (FTIR) analysis. Polymer evolution from room temperature to 1100°C is also studied by FTIR, Raman spectroscopy, and XRD techniques. Based on the obtained results, it is suggested that the hierarchal and complicated ink-bottle pore network with a high surface area besides super micropores in the sulfonated-PDVB microspheres has served as nano-sized reaction media. These pores, hereafter referred as "dynamic nanoreactors", are expected to have confined the in-situ produced thermal decomposition products containing broken bond benzene rings, while changing dimensionally and structurally during the designed carbonization regime. This confinement has led to the benzene rings fusion at 250°C, a remarkable extension of them at 450°C, their growth to graphene sheets at 900°C and finally, the stacking of curved graphene layers at 1100°C. The results of this research put stress on the capability of nanopores as nanoreactors to facilitate reactions of decomposition products at low temperatures and ambient pressures to form stacked layers of graphene; A transformation that normally requires catalysts and very high pressures for only specific polyaromatic hydrocarbons.

Bimetallic MXene with tailored vanadium d-band as highly efficient electrocatalyst for reversible lithium-oxygen battery

Lithium-oxygen (Li-O2) battery possesses high theoretical energy density of ∼ 3500 Wh kg-1, yet the sluggish kinetics of oxygen redox reactions hinder its practical application. Herein, TiVC bimetallic MXene solid solution is prepared as the efficient electrocatalyst for Li-O2 battery. The results of experiment and theoretical calculations reveal that through the formation of Ti-C-V bond in TiVC, electrons transfer from V site to Ti site enhances electron delocalization of V sites, which causes the upshift of d band center of V site and strengthens the adsorption of intermediate products (LiO2) on TiVC electrode surface. Due to the strong adsorption of intermediates, the film-like Li2O2 can be formed on TiVC electrode via the surface-adsorbed pathway, which ensures the full contact between the electrode and discharged product and thus facilitates the charge transfer between TiVC electrode and oxygen species during charge process. As a consequence, the TiVC based Li-O2 battery exhibits superior electrochemical performance including large discharge capacity (12780 mAh/g) and extended cycling stability (422 cycles) at the current density of 300 mA g-1.

Confined covalent organic framework anchored Fe sites derived highly uniform electrocatalysts for rechargeable aqueous and solid-state Zn-air batteries

Exploiting clean, highly efficient energy storage and conversion device like Zn-air battery is of significance for alleviating the energy and environmental crises of this society. Metal organic coordination polymers/frameworks have been regarded as ideal templates to synthesize non-noble metal catalysts for a long time. However, the high density of metal nodes inevitably leads to the heavy aggregation of metal nanoparticles during thermolysis transformation process, which greatly hinders the maximizing of electrochemical performances. Herein, covalent organic framework (COF) has been employed to anchor the quantificational Fe ions (COF-Fe) and then confined into the macropores of g-C3N4 to improve the dispersion of metal active sites and avoid severe aggregation during high temperature pyrolysis. After calcination, the metal nanoparticles highly dispersed Fe-CFN catalysts can be obtained. The optimal Fe-CFN-800 catalysts exhibit excellent ORR and OER performances with the potential difference between ORR and OER of merely 0.723 V. Moreover, experimental way and DFT theoretical calculations are also employed to disclose the reaction mechanism. Finally, the all-solid-state and aqueous Zn-air batteries assembled with the optimized Fe-CFN-800 as cathode present excellent performances with high peak power density, flexible rate performance, strong discharge stability and long-term charge-discharge cycling performance.