Study On Modification And Energy Storage Properties Of Cobalt-based Nanoarray Materials

Supercapacitors,are favored by many researchers because of their high power density.However,increasing their energy density is a huge challenge.In recent years,we have found that the energy density is related to the structure of the electrode material,so changing the structure of the electrode material is the starting point of our research.The selection of electrode materials plays a crucial role because they are the foundation of supercapacitors for energy storage.Here we choose metal hydroxide or metal oxide materials as electron transport materials because they have the advantages of easy preparation,high stability,and high transmittance.We know that the theoretical capacity of Co?OH?₂ is very high,but the actual capacitance(400?1200 F g^-1)is not satisfactory.In addition,Co₃O₄ has the advantages of high theoretical capacity,environmental friendliness,low cost and high cost performance.So it is also an excellent electrode material for supercapacitors.And it is also very convenient to obtain Co₃O₄ from the Co?OH?₂ through annealing.At the same time,increasing the capacitance of Co₃O₄ has become a major problem for researchers.The charge storage capacity of Co₃O₄ is limited to its conductivity,but the surface defect formation of Co₃O₄ can improve its conductivity and improve its electrochemical properties.In addition,the metal sulfide complex will improve its cycle stability,conductivity,and electrical transport performance.This paper is about the research that improves the electrochemical performance of the Co?OH?₂ and Co₃O₄ nanosheets by changing the structure of the electrode material and composition.The electrochemical properties of Co?OH?₂ nanosheet array were modified by surface exfoliating modification and surface sulfuration treatment,and the electrochemical properties of Co₃O₄ nanosheet array were modified by surface reduction modification and surface sulfuration treatment.Finally,Co?OH?₂/CoS₂ and Co₃O₄/CoS nanocomposites were prepared,which improved the energy storage performance of the materials.The main contents and research results are as follows:?1?A convenient room temperature exfoliating modification method was designed,so the Co?OH?₂ nanosheets can be exfoliated into a multilayer ultrathin nanosheets by Na⁺exfoliating method.The microstructure of Co?OH?₂ nanosheets can be controlled by changing the exfoliating time.Co?OH?₂ nanosheet arrays were obtained by hydrothermal method,and the obtained Co?OH?₂ nanosheets were soaked in a 1%NaBH₄ solution for 24 h?48 h?72 h and 96 h respectively?Co?OH?₂-24 h,Co?OH?₂-48 h,Co?OH?₂-72 h,Co?OH?₂-96 h?,the results show that the exfoliation of 72 h of Co?OH?₂-72 h has the most excellent electrochemical properties.In order to improve the conductivity,the prepared Co?OH?₂-72 h was subjected to room temperature sulfuration modification.Then Co?OH?₂-72 h was immersed in a Na2S solution at a concentration of 0.01 M for 12 h,and CoS₂ was found on the surface.The final synthesized Co?OH?₂-72h/CoS₂ composite exhibits a specific capacitance of 2536 F g^-1 at 1 A g^-1.These results can be attributed to the following factors:???The Co?OH?₂-72 h nanostructure obtained by NaBH₄ exfoliating is composed of a large number of ultra-thin nanosheets at the edges,which increases the specific surface area.This not only promotes the diffusion of the electrolyte but also increases the contact between the electrolyte and the electrode material,which makes the faraday redox reaction on the electrode surface perform fully;???CoS₂ has high theoretical capacity,excellent electrical conductivity and good stability.So the composite of CoS₂ can improve the electrochemical performance of the composite;???The electrochemical performance of monomeric nanomaterials is inferior to that of composites.In addition,the asymmetric supercapacitor has obtained the high energy density of 36 Wh kg^-1.?2?Co₃O₄/CoS composites were synthized by room temperature reduction and room temperature sulfuration.It was found that the reduction of oxygen vacancies was a key step in room temperature sulfuration.Based on the research of?1?,Co?OH?₂ was used as a precursor for air annealing to obtain porous Co₃O₄ nanosheets.The obtained Co₃O₄ nanosheets were immersed in a 1%NaBH₄ solution for 12 h,and then we obtained the material that was named R-Co₃O₄.To improve the electrochemical properties of R-Co₃O₄,R-Co₃O₄ nanosheets were immersed in a 0.01 M Na2S solution for 12 h in order to obtain a high performance R-Co₃O₄/cobalt sulfide composite.The results showed that the specific capacity of R-Co₃O₄/CoS at 1 A g^-1 was up to 1658 F g^-1 and its electrochemical performance was superior to that of Co₃O₄ nanosheets and R-Co₃O₄ nanosheets.And the capacity retention of R-Co304/CoS was 85.7%after 10.000 cycles.These results can be attributed to two factors:???using the reducing property of NaBH₄ to destroy the weak co-o bond in Co₃O₄,and generate abundant oxygen vacancy on its surface to improve the reaction efficiency;???CoS has the advantages of high theoretical capacity,excellent conductivity and stability.The combination of Co₃O₄ and CoS will increase the contact area between the electrode material and the electrolyte,which is conducive to the penetration of the electrolyte and leads to the performance improvement.