Controllable Synthesis Of Co-based Nanocrystals And Their Catalytic And Electrochemical Properties

Nowadays,many researches have achieved important progresses in the development of non-noble metal nanocrystals and their alloys with high performance in the field of new energy.Cobalt-based nanomaterials are an important group among them.Some cobalt-based nanomaterials have demonstrated excellent properties as catalysts,sensors,lithium ion batteries and magnetic materials.This dissertation mainly focuses on the preparation of CoO octahedron nanocrystals,nanospheres,hexagonal plates and rods,Co-based phosphide nanorods,Co2P/graphene nanocomposites and AuCo bimetallic nanoparticles by using high-temperature organic solution approaches.Facile one-pot and injection methods have been developed to control the crystalline phase,' composition,st:ructure and morphology of those Co-based nanocrystals.Electrochemical and catalytic properties in correlation with shape,phase and composition of these nanocrystals have been evaluated and the corresponding mechanism has been discussed.The main results are as follows:Cubic and hexagonal CoO nanocrystals exhibited excellent catalytic activities towards the hydrolysis reaction of alkaline NaBH4 solutions,which exceeded most of that of noble metal and transition metal catalysts.Their properties changed with the morphology.CoO changed into amorphous phase during catalytic reaction.The UV-vis spectra of hexagonal CoO exhibited both d-d tranisition and charge-transfer features,which was tunable in terms of the morphology,the characteristics of hexagonal CoO structure and oxygen vacancies.Ni2O,C01.33Ni0.67P and Co2P nanorods growing along[001]direction have been synthesized by injection method.For the three catalysts,Co2P nanorods showed the highest catalytic activities and stabilities toward electrocatalytic hydrogen evolution,and those of Ni2P nanorods was the lowest.The activities depended on the material of electrode and thermochemical treatment.The study verified that transition metal phosphide nanorods can be used as high performance catalysts for electrochemical hydrogen evolution.CO2P/graphene nanocomposites were successfully synthesized using a facile one-pot method.Compared to Co2P nanorods,Co2P/graphene nanocomposites exhibit more enhanced reversible cycleability and capacity toward Li-ion batteries.Particularly,the capacity increased significantly during cycling.The charge and discharge capacities reached 888 and 901 mAh g-1 respectively at the current density of 100 mA g-1,which greatly exceeds the theoretical capacities of graphene and Co2P.The enhanced properties corresponded to the plenty of microspores in Co2P/graphene,outstanding preoperties of graphene and catalytic decomposition of SEI layers.Partially phase-segregated AuCo nanoparticles with controllable compositions and structures were prepared by one-pot and injection method.Au served as a strong electron sink to promote several steps of oxygen evolution reaction(OER).AuCo nanoparticles with Au:Co ratio of?2:3 were shown to exhibit bifunctional synergy for electrocatalytic OER,in terms of its highest valent state of surface Au as strong electron sink.