Preparation Of MoO₂ And Its Surface Modification For Water Splitting

With the consumption of traditional fossil energy and intensified environmental problems,we urgently need to develop new energy and implement sustainable development strategies.Hydrogen energy has the advantages of high energy density and environmental friendliness.It is an ideal new energy carrier to meet future global energy needs.Water splitting,as a non-polluting technology that can produce hydrogen and oxygen,has attracted extensive attention.Generally,the performance of water splitting is different under different electrocatalysts.Therefore,developing electrocatalyst with high activity and stability is the key to realizing green energy production of hydrogen.Molybdenum dioxide?MoO₂?is a wide band gap semiconductor metal oxide with high free electron density in the valence band,which can improve the catalytic activity of Mo⁴⁺and has high chemical stability and electrical conductivity.While its catalytic performance is not very good,we can improve the catalytic performance of the catalyst by controlling the structure of molybdenum dioxide,inclucing defects,and constructing active sites of water splitting.In this thesis,molybdenum dioxide nanosheets were prepared on nickel?Ni?foam by hydrothermal method,and then MoO₂ nanosheets were modified by hydration of hydrazine to produce a certain amount of defects on the surface of MoO₂nanosheets.The morphology and structure were examined,and then the oxygen evolution performance and the hydrogen evolution performance were subjected to electrochemical tests.The research content of this thesis mainly includes the following aspects:?1?MoO₂ nanosheets were synthesized by a hydrothermal method on a surface of Ni foam subjected to pretreatment.Different concentrations of MoO₂ can be obtained by adjusting the concentration of the precursor solution.The morphology of the material was determined by SEM,XRD,TEM and other tests.The MoO₂ nanosheets on the Ni foam have better catalytic performance for hydrogen evolution reaction,while the catalytic performance of different amounts of MoO₂ nanosheets is smallar for oxygen evolution reaction.?2?The MoO₂ nanosheets were treated with different concentrations of hydrazine hydrate for 10 min,and the hydration hydrazine solution concentrations were:1%,2%,4%,8%.Among them,the hydrogen evolution performance of MoO₂ after 2%concentration of hydrazine treatment was the most obvious,and the initial voltage has been significantly improved.In addition,the oxygen evolution performance of MoO₂was higher than that of other conditions after 2%hydration with hydrazine for 10 min.?3?The MoO₂ nanosheets were treated with 2%hydrated hydrazine for different time to explore the optimal conditions for surface modification of MoO₂.The morphology,phase structure,elemental composition and atomic structure of the treated sample were analyzed by XRD,SEM,XPS,TEM and other testing methods.The electrochemical test showed that the MoO₂ electrolyzed water had the best performance after treatment 2%concentration of hydration for 20 min,the starting voltage is-60 mV?vs.RHE?,the Tafel slope is 67 mV/dec,the internal resistance is relatively small,and the stability is good.Similar results were obtained for its oxygen evolution performance.It was found that a certain amount of defects on the surface of MoO2 could improve its catalytic performance.