Assembling mesoporous ZnxCo3-xO4 fibers with interconnected nanocrystals via a topotactic conversion route for enhanced performance Lithium-ion batteries

Unveiling the mechanism of sodium ion storage for needle-shaped ZnxCo3-xO4 nanosticks as anode materials

The interest in the development of micro-nanostructured metal oxides has been increasing recently because of their advantages as electrode materials in energy storage applications. In this study, dandelion-like ZnxCo3-xO4 microspheres assembled with porous needle-shaped nanosticks were synthesized by co-precipitation followed by a post-annealing treatment. The open space between neighboring nanosticks enables easy infiltration of the electrolyte; therefore, each nanostick is surrounded by the electrolyte solution, which ensures proper utilization of the active material during the electrochemical reaction. The dandelion-like ZnxCo3-xO4 hierarchical microspheres exhibit a greatly improved electrochemical performance with a high capacity and good cyclability as anodes for sodium-ion batteries (SIBs). A high initial reversible capacity of 612 mA h g-1 (at 35 mA g-1, ∼0.04C) is obtained and a capacity of 349 mA h g-1 is retained after 200 cycles. Meanwhile, the electrode shows a high rate performance with a capacity of 246 mA h g-1 at 2.0C-rate. The conversion of ZnxCo3-xO4 with Na is followed by ex situ X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM) in different sodiation/de-sodiation states during electrochemical cycling. These analyses reveal that Na insertion/extraction is followed by complete reduction/oxidation of both metallic cobalt and zinc. The development of metallic Co and Zn after complete discharge and the formation of Co3O4 and ZnO when the electrode was fully recharged were identified by ex situ TEM analysis. In addition, the ZnxCo3-xO4 anode demonstrates feasible operation in a full cell by pairing with a NaNi2/3Bi1/3O2 cathode, affording a sodium-ion battery with an average working voltage of 2.6 V.

Interconnected Copper Cobaltite Nanochains as Efficient Electrocatalysts for Water Oxidation in Alkaline Medium

The present work is focused on the protective-agent-free synthesis of interconnected copper cobaltite (Cu_0.3Co_2.7O₄) nanochains by temperature-controlled solvothermal method followed by post-thermal treatment of the precursors. Furthermore, Cu_0.3Co_2.7O₄ interconnected nanochains are employed as electrocatalyst for water oxidation in alkaline medium for the first time. Extensive studies of physiochemical properties showed the formation of interconnected 1D nanochains of Cu_0.3Co_2.7O₄ exhibiting a larger specific surface area (139.5 m² g^-1) and enhanced electrochemical water oxidation ability. It delivered excellent mass activity (∼50.0 A g^-1), high anodic current density (∼124.9 mA cm^-2 at 1.75 V versus reversible hydrogen electrode), and turnover frequency (∼4.26 × 10^-2 s^-1) in 1.0 M KOH. These Cu_0.3Co_2.7O₄ nanochains also demonstrated low overpotential (∼351 mV) and good cycling stability (1000 cycles) in strong alkaline media. The fabricated Cu_0.3Co_2.7O₄ nanochains could be a good alternative to the commercial OER electrocatalysts (RuO₂ and IrO₂) and also advantageous to the development of efficient, cost-effective, and durable electrocatalysts for electrochemical water splitting.

Synthesis of porous CoMoO4 nanorods as a bifunctional cathode catalyst for a Li-O2 battery and superior anode for a Li-ion battery

We report the synthesis of porous CoMoO₄ nanorods and their applications in lithium oxygen (Li-O₂) and lithium ion (Li-ion) batteries. The unique porous structures of CoMoO₄ nanorods can promote the permeation of electrolyte and benefit the transport of lithium ion. When employed as the cathode catalyst for a Li-O₂ battery, CoMoO₄ nanorods deliver an improved discharge capacity (4680 mA h g^-1), lower charge potential and better cycle stability (41 cycles at 500 mA h g^-1 capacity limit) compared with the bare carbon. When employed as an anode in Li-ion batteries, CoMoO₄ nanorods can retain a capacity of 603 mA h g^-1 after 300 cycles (400 mA g^-1) and exhibit excellent rate capability.