Controllable Preparation Of Special Micro/nano Structure Cobalt-based Oxides And Its Application

Cobalt-based oxides are one type of the most important transition metal oxides materials because of their unique physicochemical and magnetic properties.At present,nanosized cobalt-based oxides are widely used in the fields of electrochemistry,catalysis,magnetic materials,gas sensors and so on.The phase,crystallinity,active specific surface area,morphology and structure of the nanomaterials have significant effects on their performance.In order to make the large-scale applications of those nanomaterials possible,we designed and massively fabricated cobalt-based oxides with special micro/nano structure by hydrothermal/solvent thermal method,which showed excellent performance in lithium storage of lithium ion battery and catalytic hydrolysis of ammonia borane for hydrogen production.Specific research in this work include the following three aspects:First,one-dimensional nanomaterials have bright prospect in the field of electrode materials.We synthsized Cu_0.6Ni_0.4Co₂O₄nanowires by a hydrothermal method.The electronic conduction and lithium ion diffusion coefficient of as-obtained nanowire anode material were significantly improved,which was attributed to both the special structure of the one-dimensional nanomaterials and the synergistic effects among three transition metal elements.The results show that one-dimensional nanometer can not only facilitate electron conduction,but also relieve the stress of volume variation during charge and discharge.Different transition metal elements are introduced to adjust the ion/electron conductivity and lithium storage voltage of the cobalt-based oxide electrode materials.The Cu_0.6Ni_0.4Co₂O₄nanowires obtained at the optimal synthetic conditions can maintain the specific capacity of 880 m Ah g^-1for 50cycles at 50 m A g^-1,showing a very high reversible specific capacity,excellent rate performance and cyclic stability.Second,the hollow nanostructures are widely concerned by researchers due to their great potential in different applications.By using trisodium citrate as complexing agent,Co₃O₄with different hollow structures is obtained by controlling the hydrothermal synthesis conditions,which include multi-shell hollow structure,yolk-shell structure and nano-sheets structure.The structure and electrochemical properties of those materials were characterized by XRD,FTIR,SEM,TEM,BET,XPS,Raman spectrum,TG,constant current charge-discharge test,cyclic voltammetry testing and EIS measure.The results showed that the multi-shell hollow structure had excellent electrochemical performance,including cyclic stability,rate performance,pseudo-capacitance contribution,etc.Under the optimal conditions,the sample maintained the specific capacity of 1012 m Ah g^-1after 200 cycles at 0.5 C.The specific capacity is 550 m Ah g^-1at 2 C.By comparing and observing the changes in the morphology of the polar slices with different number of cycles,it was found that the multi-shell hollow Co₃O₄could be transformed into a more open sphere structure after long cycles,which would be more conducive to easing the volume expansion and further contacting between electrode and electrolyte.Third,cobalt-based oxides are typical non-noble metal catalysts.Cu_xCo_1-xMo O₄nanorods were loaded onto the graphitic carbon nitride?g-C₃N₄?as an efficient catalyst towards hydrolysis of ammonia borane for hydrogen production.The effects of the molar ratios of Cu to Co on the structures and catalytic performance of obtained catalysts were investigated.The results indicated that when the molar ratio of Cu to Co was 4:6,the catalytic activity exhibited the highest catalytic performance.The Cu_0.4Co_0.6Mo O₄nanorods have good catalytic performance by themselves,and the catalytic performance can be further enhanced by the loading them onto g-C₃N₄.The TOF values of the catalysts before and after the loading on g-C₃N₄are 17.6 and 75.7mol _H2mol_cat^-1min^-1,respectively.Compared with other non-noble metal catalysts in the literatures,Cu_0.4Co_0.6Mo O₄/g-C₃N₄is a high-performacing catalysts in terms of TOF.A series of cobalt-based oxide nanomaterials with special morphology were designed and constructed by scalable hydrothermal method.The relationship between material structure and properties was studied.Therefore,this work has crucial theoretical significance and practical value.