Investigation On Electrochemical Performance Of Crystalline-Amorphous Heterogeneous Phase Materials Based On Cobalt Boride

As the electrode material of supercapacitors,bimetal oxides have higher electrochemical activity than single metal oxides and can undergo multiple Faraday reactions,so they have a relatively high theoretical specific capacity.However,due to the limitation of low conductivity,their actual specific capacities are much lower than the theoretical values.Especially at high current density,electron transfer is slow,which affects its rate performance.In order to solve this problem,a crystalline-amorphous heterogeneous phase engineering strategy was proposed.When two materials with different degrees of crystallinity are combined,a crystalline-amorphous heterogeneous phase interface will be formed.On the one hand,it can improve the ohmic contact between the electron transport layer and the electrode-electrolyte,provide more electrochemically active sites and promote ion diffusion and electron transport.On the other hand,the amorphous phase has structural defects arranged in disorder,which can effectively adapt to the volume change in the redox process and increase the specific capacity.Based on the above discussion,we have constructed a series of crystalline-amorphous heterophase composite nanomaterials with Co-B as amorphous phase and CoMoO₄,NiMoO₄,Co₃V₂O₈,Ni₃V₂O₈,CoWO₄,and NiWO₄ as crystalline phases,respectively,and then studied their electrochemical properties.The main research contents and results are as follows:CoMoO₄,NiMoO₄,Co₃V₂O₈,Ni₃V₂O₈ were synthesized by the water bath method,CoWO₄,and NiWO₄ were synthesized by hydrothermal method.Subsequently,the CoMoO₄/Co-B rod-like mixed structure,NiMoO₄@Co-B rod-like core-shell structure,Co₃V₂O₈@Co-B spherical core-shell structure,Ni₃V₂O₈@Co-B spherical core-shell structure,CoWO₄/Co-B composite nanostructure,and NiWO₄/Co-B composite nanostructure were sequentially synthesized by the liquid-phase reduction method,and regulate the crystalline phase and the amorphous phase proportion.The electrochemical performances of the single-electrode are measured in the 6 M KOH electrolyte.The CoMoO₄/Co-B,NiMoO₄@Co-B,Co₃V₂O₈@Co-B,Ni₃V₂O₈@Co-B,CoWO₄/Co-B,and NiWO₄/Co-B electrode materials with the best crystalline-amorphous mass ratios exhibit specific capacities of 436,2025,552,1789,430,and 319 F g^-1 at 0.5 Ag^-1,respectively,which are all higher than the corresponding bimetal oxide under the same test conditions(CoMoO₄:202 F g^-1,NiMoO₄:1004 F g^-1,Co₃V₂O₈:321 F g^-1,Ni₃V₂O₈:1232 F g^-1,CoWO₄:137 F g^-1,NiWO₄:182 F g^-1).When the current density is increased from 0.5 Ag^-1 to 10 Ag^-1,the capacity retention rate of the CoMoO₄/Co-B,NiMoO₄@Co-B,Co₃V₂O₈@Co-B,Ni₃V₂O₈@Co-B,CoWO₄/Co-B,and NiWO₄/Co-B electrode are 66%,86%,67%,63%,66%,and 73%,respectively.Except for CoMoO₄/Co-B,they are all higher than the corresponding bimetal oxides(CoMoO₄:77%,NiMoO₄:46%,Co₃V₂O₈:64%,Ni₃V₂O₈:38%,CoWO₄:66%,NiWO₄:51%).The assembled crystalline-amorphous heterogeneous phase composite material//activated carbon hybrid supercapacitors also exhibit excellent specific capacity,power density,and energy density.Also,the effect of adding different qualities of activated carbon conductive additives on the electrochemical performance of Co-B electrodes was explored.The results of single-electrode electrochemical tests show that the best Co-B/activated carbon electrode has a specific capacity of 412 F g^-1 at a current density of 0.5 Ag^-1,which is higher than that of Co-B(276 F g^-1).When the current density is increased from 0.5 Ag^-1 to 10 Ag^-1,it exhibits a rate performance of 75%.The assembled Co-B/activated carbon composite material//activated carbon hybrid supercapacitor also has an excellent electrochemical performance.Through the above research,we have preliminarily proved that the construction of crystalline-amorphous heterogeneous phase helps to improve the specific capacity and rate performance of the electrode material,and the morphology and structure of the electrode material will also affect the electrochemical performance to a certain extent.In addition,other types of crystalline-amorphous phase materials can also be synthesized and applied in the field of energy storage.