Preparation And Physicochemical Properties Of Cobalt-based Oxide Materials

Transition metal oxides have been widely studied in the fields of supercapacitors,electrochemical storage and chemical catalysis,etc.As a transition metal element,cobalt has a variety of chemical valence states,resulting in the formation of a variety of polyoxides with different physical and chemical properties.Some studies have confirmed that cobalt oxide has good catalytic potential.In this thesis,the decomposition of hydrogen peroxide by different phases of cobalt perovskite materials is studied.At the same time,with the in-depth study of two-dimensional materials,layered van der Waals materials have attracted the attention of researchers due to their unique properties.The alkaline cobalt oxide?M_xCo₂o₄,M=Na,K,Rb?is a layered oxide,whose hexagonal structure contains the CoO₂ layer intercalated with the alkali metal.Some literatures have reported the superconductivity,giant magnetoresistance and magnetism of layered alkali metal oxides.However,the synthesis of the large single crystal of layered M_xCo₂O₄ was seldom reported.In this thesis,we developed a convenient melton salts synthesis method of layered M_xCo₂O₄single crystals.And some physical and chemical properties of the crystals were tested.The main research results of this paper include the following four parts:1.Strontium cobalt oxide with hexagonal phase?H-SCO?,square phase?O-SCO?and tetragonal phase?T-SCO?were prepared respectively.The catalytic activity of strontium cobalt acid with three topological phases?H-SCO,O-SCO and T-SCO?for the decomposition of hydrogen peroxide was studied.It was found that the catalytic activity of T-SCO was the best,and the activation energy of strontium cobalt acid with different phases was fitted by Arrhenius formula.The degradation of rhodamine B in hydrogen peroxide solution with H-SCO,O-SCO and T-SCO as catalysts was compared.The degradation rate of Rhodanmine B was the fastest in the advanced oxidation reaction catalyzed by T-SCO.2.Developed a general synthesis method to grow a variety of layered alkali cobaltite oxide single crystal:Na_xCo₂O₄?NCO?,K_xCo₂O₄?KCO?and Rb_xCo₂O₄?RCO?,alkali metal cobalt oxide all in black,with metallic luster,NCO,X-ray diffraction pattern of KCO and RCO respectively corresponding to the PDF CARDS:27-0682,32-0768and 27-051,X ray diffraction spectrum analysis showed that the growth of crystals have obvious preferred orientation,the c axis,slow growth ab in-plane preferential growth.NCO,KCO and RCO have similar crystal structures,and the cobalt oxide layers are filled with alkali metals?Na,K,Rb?.3.The resistances of NCO,KCO and RCO increase with the increase of temperature in the range of 10k-300k,which indicates that the alkali cobalt oxide NCO,KCO and RCO are not intrinsic semiconductor materials and have certain metallic properties.The magnetic properties of NCO,KCO and RCO were measured to find that NCO was paramagnetic,whereas KCO and RCO were antiferromagnetic with the critic temperature of 30k.This may be due to KCO and RCO magnetic ground state is long-range disorder short-range order spin glass state,short-range ordered the spin magnetic moment,on the other hand,tend to the magnetic moment of similar antiferromagnetic alignment.4.NCO,KCO and RCO was microwave dispersed in deionized water or ethanol with adding different amount of carbon black.And their electrochemical oxygen evolution catalytic activities were investigated to find that the electrochemical catalysis activity of NCO,KCO and RCO increased significantly with the addition of a small amount of carbon black,but with the further increase of carbon black,the catalytic activity of alkali cobalt oxides began to deteriorate.It was found that the electrochemical catalysis performance of alkali cobalt oxides dispersed by alcohol ultrasound was better than that of the same alkali cobalt oxides dispersed by deionized water.