Preparation Of C_o3O₄ Matrix Composites And Their Electrochemical Performance

Co₃O₄ is a promising alternative catalyst toward Oxygen Evolution Reaction?OER?owing to its highly efficiency activities,stable,inexpensive.In addition,Co₃O₄ can also be used as a lithium ion battery anode material due to its high theoretical specific capacity(890 m Ah g^-1),good operational safety and moderate cost.However,practical applications have not been realized due to its low electrical conductivity and severe particle agglomeration.In this paper we optimized the composition morphology and structure to improve the electrochemical performance of Co₃O₄ as follows:Co₃O₄ quantum dots were hierarchically assembled on ultra-thin Mn O₂nanosheets?Mn O₂/Co₃O₄?based on van der Waals interactions.This Mn O₂/Co₃O₄bydrid materials can be used as high performance dual-function electrocatalysts of OER and HER?Hydrogen Evolution Reaction?.Small overpotential of 350 m V was needed toward OER to reach the current density of 10 m A cm^-2,which was close to the precious metal oxide Ru O₂?320 m V?.For HER,the overpotential to reach the current density of 10 m A cm^-2was 122 m V in alkaline medium.This assembly method effectively avoids the agglomeration of Co₃O₄ quantum dots,ensures that the material has a large specific surface area,which can provide sufficient active sites for electrochemical reactions.In addition,it also uti lizes the catalytic activity of Mn O₂ and Co₃O₄,which enables MnO₂/Co₃O₄ materials to exhibit excellent electrochemical performance.In order to further improve the conductivity of Co₃O₄-based materials,a novel dandelion-like Co₃O₄ mesoporous nanomaterial supported by Cu foam was obtained by one-step hydrothermal followed by annealing.The dandelion-like Co₃O₄@Cu foam composites can exhibit excellent OER performance as OER materials.At a current density of 10 m A cm^-2,the required overpotential of Co₃O₄@Cu foam is only 192 m V.The Tafel slope of Co₃O₄@Cu foam is also very small(42.8 m V dec^-1).Co₃O₄@Cu foam almost retains a constant current density after 11 h stabilization,verifying a good durability.The dandelion-like Co₃O₄@Cu foam composite can also exhibit excellent cycle stability and rate performance as a negative electrode material for lithium ion battery.At a current density of 2 C,the discharge specific capacity can still reach 882 m Ah g^-1after 100 cycles,the material exhibits excellent large rate discharge performance,when the current density up to 5C,the discharge specific capacity can still reach 630 m Ah g^-1.The dandelion-like Co₃O₄@Cu foam composite material can exhibit excellent electrochemical performance mainly due to the following reasons:?1?high conductivity and large active area of Cu foam;?2?fast reaction power of dandelion-like Co₃O₄ mesoporous materials learn..To reduce costs,a hierarchical array structure Cu₂O@Co₃O₄/Cu foam composed of Cu foam,Cu₂O nanowires and Co₃O₄ nanosheets was prepared by solution impregnation and electrodeposition method.The 3D core-shell Cu₂O@Co₃O₄/Cu foam exhibits excellent OER performance.Small overpotential toward OER of 223 m V was needed to reach the current density of 10 m A cm^-2.This indicating that the OER performance of the 3D core-shell Cu₂O@Co₃O₄/Cu foam is much better than Ru O₂.Excellent stability can be achieved as there is almost no current density attenuated after 12 hours stability test.Used as a negative electrode material for lithium batteries,this core-shell structure of Cu₂O@Co₃O₄/Cu foam shows good lithium storage performance.At a current density of 500 m A g^-1,the capacity can be improved to 1090 m Ah g^-1after 200 cycles,even when the current density is 5000 m A g^-1,the discharge specific capacity can still reach 600 m Ah g^-1.This excellent performance achieve the advantages from the synthesized Cu₂O nanowires closely attached to the Cu foam,which can shorten the path length of ion diffusion and electron transport.Morever,the Cu₂O@Co₃O₄ array structure facilitates uniform distribution and rapid diffusion of ions and the core-shell material has a larger specific surface area,which ensures that more materials is in contact with the electrolyte and provides a large amount of active sites for electrochemical reactions,enabling it to exhibit excellent electrochemical performance.