Synthesis Of Nano ?-Co(OH)2 And Applications In Electrochemistry

Traditional noble metal electrocatalysts such as RuO₂ and IrO₂ have the disadvantages of low crustal reserves and high cost,so it is urgent to develop alternative materials with low price and excellent performance.Currently,layered cobalt hydroxide?Co?OH?₂?has the advantages of relatively simple preparation,low cost,non-toxicity and high electrochemical activity,so it has been widely used in the fields of water electrolysis catalysts,supercapacitors,electrochemical detection sensors and so on.The crystal phase of Co?OH?₂ mainly includes?phase and?phase,among which?-Co?OH?₂ has higher electrochemical performance.Therefore,?-Co?OH?₂ has become a popular material for electrolytic water catalysts and electrode materials for supercapacitors.However,the existing preparation methods of?-Co?OH?₂ are complex,especially the preparation of nano?-Co?OH?₂ with large specific surface area is not easy,and its electrocatalytic activity needs to be further improved.Therefore,In this thesis,we have launched research on the preparation method of nano?-Co?OH?₂,developed a rapid preparation method of nano?-Co?OH?₂,and systematically studied its application in electrocatalytic oxygen evolution reaction.The electrocatalytic activity of?-Co?OH?₂ was further optimized through the doping of transition metal elements.The application in supercapacitor was also investigated to find that the composite material has good specific capacitance and good performance by combined with multi-walled carbon nanotubes.The research work of this paper mainly includes the following three parts:1.We developed a the rapidly synthesis method of nano?-Co?OH?₂ via coprecipitation,which was mediated by ammonia using the mixture of water and methanol as solvent.We systematically investigated the effect of the volume ratio of methanol and water to the electrocatalytic performance to find that it gave rise to the best catalytic activity for electrochemical oxygen evolution with the ratio of 1:3.Its onset potential was 1.4 V and overpotential was 340 mV at the current density of 10mA cm^-2,which was significant better than prepared by using only water as solvent.The morphologies of nano?-Co?OH?₂ were futher characterized,which the flower-like nanostructures were obtained using the mixture of methnol and water.Whereas the aggragated?-Co?OH?₂ was received using water as solvent.The results showed that the mixture of water and methanol was beneficial to the formation of flower-liked?-Co?OH?₂ and had obvious solvent effect.2.Basing on the synthesis method of flower-liked nano?-Co?OH?₂,the transition metal doped?-Co?OH?₂ were synthesized via adding transition metal compound,such as FeCl₂,CuCl₂,NiCl₂.The flower-like nanostructures were kept for the Cu and Ni-doping?-Co?OH?₂,while Fe-doped?-Co?OH?₂ present the nanoparticle morphology.Electrochemical tests showed that the oxygen evolution reaction performance of transition metal doped?-Co?OH?₂ had better oxygen evolution performance than?-Co?OH?₂.The influence of transition metal doped concentration were futher optimized to find that Fe-Co?OH?₂ with 20%doped concentration presented the best oxygen evolution reaction activity with the overpotential was only 290 mV at a current density of 10 mA cm^-2.In addition,the application in glucose electrochemical dection for transition metal doped?-Co?OH?₂ were also investigated to find that the 30%Cu-doped Co?OH?₂ showed the best activity.3.MWCNTs/?-Co?OH?₂ composite materials were synthesized via combining?-Co?OH?₂ with multi-walled carbon nanotubes?MWCNTs?.Through morphological characterization,it was found that the flower-liked nano?-Co?OH?₂ was successfully grown on the surface of MWCNTs.The applications of MWCNTs/?-Co?OH?₂nanocomposites as electrode materials were investigated to find that it presented the excellent storage capacity with the specific capacitance of 1027 F/g at 2 A/g current density.At the same time,the material also exhibits good cycle stability.After 2000repeated charge and discharge tests,the specific capacity retention rate was 84%.