Layered buserite Mg-Mn oxide cathode for aqueous rechargeable Mg-ion battery

Owing to the features(high safety,inexpensive and environmental friendliness)of aqueous rechargeable Mg-ion batteries(ARMIBs),they have drawn extensive attention in the future energy storage systems.However,the poor Mg^(2+)migration kinetics during the Mg^(2+)intercalation/extraction still hinders the progress of developing suitable cathode materials.Herein,a layered buserite Mg-Mn oxide(MMO)material with large interlayer space(~9.70A)and low-crystalline structure is studied as a high-performance cathode in ARMIBs.Compared with the counterpart,the Mg^(2+)migration kinetics of the MMO cathode can be enhanced by its unique structure(bigger interlayer spacing and low-crystalline structure).The layered buserite MMO as a high-performance ARMIBs cathode exhibits high Mg storage capacity(50 mAg^(-1):169.3 mAh g^(-1)),excellent rate capability(1000 mAg^(-1):98.3 mAh g^(-1)),and fast Mg^(2+)migration(an average diffusion coefficient:~4.21×10-^(10)cm^(2)s^(-1))in 0.5 M MgCl_(2)aqueous electrolyte.Moreover,the MMO-1//AC full battery achieved a high discharge capacity(100 mAg^(-1):111 mAh g^(-1)),and an ignored fading over 5000 cycles(1000 mAg^(-1)).Therefore,layered Mg-Mn oxide with large interlayer space may break a new path to develop the promising ARMIBs.

Metal-organic frameworks derived low-crystalline NiCo_(2)S_(4)/Co_(3)S_(4) nanocages with dual heterogeneous interfaces for high-performance supercapacitors

Nickel cobalt bimetallic heterogeneous sulfides are attractive battery-type materials for electrochemical energy storage.However,the precise synthesis of electrode materials that integrate highly efficient ions/electrons diffusion with abundant charge transfer channels has always been challenging.Herein,an effective and concise controllable hydrothermal approach is reported for tuning the crystalline and integrated structures of MOF-derived bimetallic sulfides to accelerate the charge transfer kinetics,and thus enabling rich Faradaic redox reaction.The as-obtained low-crystalline heterogeneous NiCo_(2)S_(4)/Co_(3)S_(4)nanocages exhibit a high specific capacity(1023 C/g at 1 A/g),remarkable rate performance(560 C/g at 10A/g),and outstanding cycling stability(89.6%retention after 5000 cycles).Furthermore,hybrid supercapacitors fabricated with NiCo_(2)S_(4)/Co_(3)S_(4)and nitrogen-doped reduced graphene oxide display an outstanding energy density of 40.8 Wh/kg at a power density of 806.3 W/kg,with an excellent capacity retention of 88.3%after 10000 charge-discharge cycles.

Low Li ion diffusion barrier on low-crystalline FeOOH nanosheets and high performance of energy storage

To obtain symmetric supercapacitors(SCs)with high energy density,it is critical to fabricate an electrode with wide potential window and excellent capacitive performance.Herein,by using the strong double hydrolysis reaction between anions and cations,the FeOOH nanosheets on the surface of activated carbon cloth(FeOOH@AC)are prepared through a simple hydrothermal process.The FeOOH@AC electrode exhibits maximum capacitance of 4,090 mF·cm^−2 at wider potential window-1–0 V and 3,250 mF·cm^−2 at 0–1 V versus SCE in 2 M LiNO3 electrolyte.With two pieces of FeOOH@AC electrodes the obtained symmetric SC can operate at the voltage window of 2 V.This FeOOH symmetric SC shows high energy density of 13.261 mWh·cm^−3 at a power density of 14.824 mW·cm^−3 and maintains 4.175 mWh·cm^−3 at a maximum power density of 118.564 mW·cm^−3,as well as excellent charge storage capacity and cyclic stability.Li ion adsorption and diffusion mechanism on the(200)facets of FeOOH are explained by the density functional theory(DFT)calculations.The simple synthesis process and excellent capacitance performance of the FeOOH@AC composite make it a very promising candidate for high performance symmetric SC electrodes.

Activating surface atoms of high entropy oxides for enhancing oxygen evolution reaction

High entropy oxides(HEOs) have attracted extensive attention of researchers due to their remarkable properties. The electrocatalytic activity of electrocatalysts is closely related to the reactivity of their surface atoms which usually shows a positive correlation. Excellenet stability of HEOs leads to their surface atoms with relative poor reactivity, limiting the applications for electrocatalysis. Therefore, it is significant to activate surface atoms of HEOs. Constructing amorphous structure, introducing oxygen defects and leaching are very effective strategies to improve the reactivity of surface atoms. Herein, to remove chemical inert, low-crystallinity(Fe, Co, Ni, Mn, Zn)_(3)O_(4) (HEO-Origin) nanosheets with abundant oxygen vacancies was synthesized, showing an excellent catalytic activity with an overpotential of 265 mV at 10 mA/cm^(2), which outperforms as-synthesized HEO-500℃-air(335 mV). The excellent catalytic performance of HEO-Origin can be attributed to high activity surface atoms, the introduction of oxygen defects efficiently altered electron distribution on the surface of HEO-Origin. Apart from, HEO-Origin also exhibits an outstanding electrochemical stability for oxygen evolution reaction(OER).