Preparation,Characterization And Electrochemical Properties Of Cobalt-Based Compounds

It is significant to make the conversion of electrical energy into various chemical energy and store it up in today's society.Nowadays,the conversion,storage and release of all kinds of clean energy to electric energy are important parts of the green energy development.And the development and usage of green energy will improve the social energy structure and promote social development.However,with the continuous development of society,the storage requirements for all kinds of energy are also increasing,catalysts of hydrogen production for fuel cell precursors need to be more efficient,and lithium-ion batteries and sodium-ion batteries require better cycle performance,higher energy density and power density.Therefore,it is necessary to study and make new materials in order to meet a variety of new requirements.According to the survey,transition metal can conform to what are required above by purposefully designing,so transition metal composites can be widely studied andapplied in life.Due to the good performance of cobalt-based compounds,many researchers are studying on it.However,the performance of their research products were not very prominent,mainly because the structural design of the material was not outstanding.So it is necessary to improve the electrochemical performance of the material by specifically designing the material structure and increasing the conductivity of the material.In this thesis,three kinds of composites of cobalt-based compounds and carbon materials were synthesized and their electrochemical properties were studied.The first one was a rGO/CoWSx composite,which was obtained hydrothermally by dispersing ammonium tetrathiotungstate and cobalt nitrate in a solution of graphene oxide.The second one was a Co9S8@C composite.By synthesizing ZIF-67,a common metal organic framework,as a template,and adding dopamine to it,a hollow structure precursor of ZIF-67@PDA was formed.Then using thiourea as a sulfur source for vulcanization to obtain the Co9S8@C composite.The third one was a CoP@C composite,which was obtained by using sodium hypophosphite to phosphatize the precursor of the second synthetic.The relevant electrochemical properties of the synthesized three materials were tested.And TEM,XRD,SEM,XPS and other characterization methods were used to find the most suitable experimental conditions to obtain the required materials.The specific content is as follows:1.CoWSx partticles which grew on graphene was used as an electrocatalytic hydrogen evolution material.By controlling the synthesis temperature,synthesis ratio and other conditions,the structure of CoWSx nanoparticles loaded on graphene was prepared.By comparing the catalytic performance to select the appropriate parameters,the material under the most suitable parameters was characterized.It was found that when the ratio of ammonium tetrathio-tungstate and cobalt nitrate was 1:1,the nano-particles exhibited the best performance.By testing the electrode hydrogen evolution curve,the hydrogen evolution potential was-71 mV,and had a very low Tafel slope which was 55mV dec-1.The rGO/CoWSx had good cycle stability which was proved by undergoing constant pressure cycling and repeated line sweeping.2.The Co9S8@C composite was synthesized with ZIF-67 to be a lithium ion battery anode material.The structure stability of the material was ensured by introducing dopamine coating as a carbon source,and the product was synthesized by controlling the concentration of coating and by the way of two-step vulcanization.As a lithium ion battery anode material,its performance was studied.It was found that this material had good electrical conductivity and structure.It can maintain a reversible capacity of 760 mAh g-1 after 200 cycles charge-discharge test at a current density of 0.5A g-1,It also exhibited an excellent capacity of 290 mAh g-1 at 2A g-1.3.The CoP@C composite was synthesized with ZIF-67 to be a sodium ion battery anode material.The structure stability of the material was ensured by introducing dopamine coating as a carbon source,and the product was synthesized by the way of two-step vulcanization.As a sodium ion battery anode material,its performance was studied.It was found that this material had good circulation performance.It can maintain a reversible capacity of 200 mAh g-1 after 700 cycles charge-discharge test at a current density of 0.5A g-1.The reversible capacity was able to maintain 130 mAh g-1 even at 2A g-1.