Sythesis Of Cobalt-Based Nanomaterials With Controlled Compositions And Architectures For Electrochemical Energy Storage And Conversion

Electrochemical energy storage and conversion is suitable for current energy development,due to its high efficiency,good safety performance and environmental protection.Meanwhile,the development of new energy materials is the key to realize its energy storage and transformation.The transition metal compounds are widely used in lithium ion batteries and electrocatalysis due to their variable valence electron structure.Herein,we chose cobalt-based nanomaterials which were low cost,high yield,high electroactive as the research objects.Three cobalt-based materials including octahedral nanoparticles self-assembled Co2(OH)3Cl microspheres,Co(OH)F nanorods and mesogenic CoSn(OH)6 nanocubes were synthesized through simple hydrothermal method.CO2(OH)3Cl microspheres and Co(OH)F nanorods were used as anode materials for lithium ion batteries and mesogenic CoSn(OH)6 nanocubes were applied to the electrocatalytic oxygen evolution reaction(OER).They all showed good performances in electrochemical energy storage and conversion.The main experimental results and research conclusions are summarized as follows:(1)In the mixed solvent of triethanolamine(TEOA)and H20,octahedral nanoparticles self-assembled Co2(OH)3Cl microspheres were prepared by hydrothermal method.Then we changed the synthetic parameters such as the type of the solvent,the amount of triethanolamine,hydrothermal temperature and hydrothermal reaction time to confirm the effects of different conditions on the composition and structure of the products.It was demonstrated that the weak alkaline medium and coordination environment provided by TEOA played important roles on the formation of the Co2(OH)3Cl and the self-assembling of the octahedral nanoparticles into microspheres.More importantly,these Co2(OH)3CI microspheres exhibited excellent capacitance,cycle stability and rate performance than that of CoCl2 and Co(OH)2 materials when assembled as lithium ion half-cells.The initial discharge specific capacity of Co2(OH)3C1 electrode was 1492 mAh g-1 at a current density of 4 A g-1.After 500 cycles,the specific capacity still remained 850 mAh g-1 and the capacity retention rate was 81.1%.The excellent performance may attribute to the synergistic effect of chloride ion and hydroxide ion.We got chlorine-doped Co3O4 microspheres via calcinating CO2(OH)3Cl at 400?.The specific capacity of chlorine-doped Co304 electrode was 547 mAh g-1 at a current density of 2 A g-1.After 500 cycles,the capacity retention rate was still as high as 86.7%.(2)In the mixed solvent of triethanolamine(TEOA)and H,O,nanorod-like Co(OH)F electrode material with the length of about 1 ?m and the diameter of 40-60 nm was prepared by optimizing the reaction parameters and synthesis conditions.The results showed that,TEOA also played an important role on the formation of the nanorods Co(OH)F products in this synthesis system.When they were used as anode materials for lithium-ion batteries,Co(OH)F nanorods exhibited better lithium storage performance than CoF2 and Co(OH)2.The specific capacity of Co(OH)F electrode was 698 mAh g-1 at a current density of 1 A g-1.After 200 cycles,the capacity retention rate still reached 96.9%.The excellent performance may attribute to the synergistic effect of fluorine ion and hydroxide ion in Co(OH)F.And the 1D nanorods structure provided a high surface-to-volume ratio and high charge-transport efficiency which may also contributed greatly to the high electrochemical performance.(3)In the system of TEOA-H20-NaOH,CoSn(OH)6 nanospheres,mesogenic CoSn(OH)6 nanocubes assembled from nanoparticles and CoSn(OH)6 nanocubes were prepared by hydrothermal method.Then the synthetic parameters were changed to confirm the effects of different conditions on the composition and structure of the CoSn(OH)6 products.The characterization results showed that the alkaline medium and crystal growth environment provided by TEOA and NaOH were the key factors for the formation of CoSn(OH)6 materials with different structures.When used as the catalyst of OER,mesogenic CoSn(OH)6 nanocubes showed superior performance.At a current density of 10 mA cm-2,the initial overpotential of mesogenic CoSn(OH)6 was 391 mV and the Tafel slope was 60 mV/dec,which were better than the cubic CoSn(OH)6 nanocrystals and CoSn(OH)6 nanospheres.The mesogenic CoSn(OH)6 could work over 10 h without dropping.The excellent electrochemical performance could attribute to the high specific surface area of the material,which increase the catalytic reaction activity sites,and further enhanced the performance of electrochmical water splitting.