| Cobalt molybdate(CoMoO4),as a bimetallic oxide,combines the excellent conductivity of cobalt element and the variable valence of molybdenum element.It has high activity for electrocatalytic reactions,and its structure of typical metal molybdate crystal lattice leads to high stability.So CoMoO4 nanomaterials show great potential in the field of electrocatalytic water splitting.In recent years,researches about it have gradually increased,but the performance of the CoMoO4-based electrocatalysts still do not meet the industrial requirements of hydrogen production from water.Especially for hydrogen production in industry,the performance of OER under the high current density is far from the actual application standards.Therefore,it is great significance to improve the catalytic performance of CoMoO4 nanomaterials.It is well known that the catalytic performance is dependent on the composition and structure of materials.For oxides,optimizing the electronic structure by producing defects of oxygen vacancies in the structure is an effective way to improve their catalytic performance.However,conventional methods for producing oxygen vacancies,such as high temperature annealing,atmosphere reduction method and mechanical ball milling method,are cumbersome and the preparation conditions are harsh.In this thesis,in order to improve the OER activity of CoMoO4 nano-flowers,a home-made microwave plasma equipment was used to rapidly generate abundant oxygen vacancies in the surface of CoMoO4 nano-flowers through the plasma etching method.This method is simple and efficient compared with conventional methods.In addition,we also successfully fabricated a core-shell composite by electrodepositing a highly active NiFe LDH onto the surface of CoMoO4 nanoflowers.The OER performance was enhanced through promoting the synergistic effect of the two components by adjusting the composition ratio and structure of the composite material.The specific research content is as follows:1.Preparation of CoMoO4 nanoflowers with oxygen vacancies and its OER performance:Firstly,CoMoO4 nanoflowers on nickel foam were synthesized using a two-step hydrothermal-calcining method.Then oxygen vacancies were generated on the surface of CoMoO4 nanoflowers by plasma etching using a home-made microwave plasma equipment.Influence of different etching time on the morphology,crystal structure and catalytic performance of CoMoO4 nanoflowers was explored.The results show that as the etching time increases,the surface of the CoMoO4 nanoflower gradually become rough,and the activity of the material also change significantly.When the etching time is 10 min,the obtained CoMoO4 nanoflower shows the best catalytic performance.When the current density is 10 mA/cm2,the OER overpotential is only 225 mV,which is significantly improved compared to the precursor.The mechanism of the enhancment of OER performanc of CoMoO4 nanoflowers with oxygen vacancies was discussed.It was found that the excellent OER performance was mainly due to the optimization of the structure of CoMoO4 nanoflowers by oxygen vacancies and the morphological changes during the etching process.The etching also increases the specific surface area and the number of active sites in CoMoO4 nanoflowers.2.Preparation of CoMoO4/NiFe LDH composites and its OER performance:CoMoO4 nanoflowers on nickel foam were prepared by hydrothermal method Then NiFe LDH nanosheets were uniformly deposited on the surface of CoMoO4 nanoflowers through simple electrodeposition technology.The composite and morphology of CoMoO4/NiFe LDH were adjusted by controlling the electrodeposition time.The composites prepared under different conditions were characterized.The results showed that as the electrodeposition time increases,NiFe LDH ultra-thin nanosheets gradually grow on the surface of the CoMoO4 nanoflowers to form a core-shell structure.CoMoO4/NiFe LDH composites prepared with different reaction times all showed better OER performance than the precursor.When the deposition time is 300 s,the CoMoO4/NiFe LDH composite exhibite the best OER performance.Its OER overpotential is only 214 mV when the current density is 10 mA/cm2.The excellent OER performance of the electrocatalyst is mainly attributed to the construction of a heterojunction which allows the two components to produce a good synergistic effect,thereby optimize the electronic structure of the electrocatalyst.At the same time,the reasonable core-shell structure maximizes the electrochemical activity specific surface area of the electrocatalyst and a large number of active sites are exposed. |
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