Unveiling the Nature of Superior Sodium Storage in the CoSe2/rGO Nanocomposite.

Sodium-ion batteries (SIBs) are considered the most promising alternatives to lithium-ion batteries (LIBs) due to the abundant availability of sodium and their cost-effectiveness. Transition metal selenides (TMSes) are considered promising anodes for SIBs due to their economic efficiency and high theoretical capacity. Nevertheless, overcoming the challenges of sluggish reaction kinetics and severe structural damage is crucial to improving cycle life and rate capability. Herein, a simple microwave hydrothermal process was used to synthesize a nanocomposite of CoSe2 nanoparticles uniformly anchored on reduced graphene oxide nanosheets (CoSe2/rGO). The influences of rGO on the structure and electrochemical performance and Na+ diffusion kinetics are investigated through a series of characterization and electrochemical tests. The resulting CoSe2/rGO nanocomposite exhibits a remarkable initial specific capacity of 544 mAh g-1 at 0.5 A g-1, impressive rate capability (368 mAh g-1 at 20 A g-1), and excellent cycle life and maintains 348 mAh g-1 at 5 A g-1 over 1200 cycles. In addition, the in situ electrochemical impedance spectroscopy (EIS), ex situ X-ray diffraction (XRD), and transmission electron microscopy (TEM) tests are selected to further investigate the sodium storage mechanism.

A Facile Microwave Hydrothermal Synthesis of ZnFe2O4/rGO Nanocomposites for Supercapacitor Electrodes.

As a typical binary transition metal oxide, ZnFe2O4 has attracted considerable attention for supercapacitor electrodes due to its high theoretical specific capacitance. However, the reported synthesis processes of ZnFe2O4 are complicated and ZnFe2O4 nanoparticles are easily agglomerated, leading to poor cycle life and unfavorable capacity. Herein, a facile microwave hydrothermal process was used to prepare ZnFe2O4/reduced graphene oxide (rGO) nanocomposites in this work. The influence of rGO content on the morphology, structure, and electrochemical performance of ZnFe2O4/rGO nanocomposites was systematically investigated. Due to the uniform distribution of ZnFe2O4 nanoparticles on the rGO surface and the high specific surface area and rich pore structures, the as-prepared ZnFe2O4/rGO electrode with 44.3 wt.% rGO content exhibits a high specific capacitance of 628 F g-1 and long cycle life of 89% retention over 2500 cycles at 1 A g-1. This work provides a new process for synthesizing binary transition metal oxide and developing a new strategy for realizing high-performance composites for supercapacitor electrodes.

Ultra-Fine Ruthenium Oxide Quantum Dots/Reduced Graphene Oxide Composite as Electrodes for High-Performance Supercapacitors.

This study synthesized ultra-fine nanometer-scaled ruthenium oxide (RuO2) quantum dots (QDs) on reduced graphene oxide (rGO) surface by a facile and rapid microwave-assisted hydrothermal approach. Benefiting from the synergistic effect of RuO2 and rGO, RuO2/rGO nanocomposite electrodes showed ultra-high capacitive performance. The impact of different RuO2 loadings in RuO2/rGO nanocomposite on their electrochemical performance was investigated by various characterizations. The composite RG-2 with 38 wt.% RuO2 loadings exhibited a specific capacitance of 1120 F g-1 at 1 A g-1. In addition, it has an excellent capacity retention rate of 84 % from 1A g-1 to 10 A g-1, and excellent cycling stability of 89% retention after 10,000 cycles, indicating fast ion-involved redox reactions on the nanocomposite surfaces. These results illustrate that RuO2/rGO composites prepared by this facile process can be an ideal candidate electrode for high-performance supercapacitors.