Study On The Controllable Synthesis And The Electrocatalytic Hydrogen Evolution Properties Of Double-shelled MoSe2/C Hollow Nanospheres

With the depletion of fossil energy and the environmental pollution accompanying with their rapid consumption,it becomes more and more urgent to find renewable and clean alternative energy resources.Hydrogen has been regarded as one of the most ideal energy storage carriers because of its advantages such as renewable energy,high calorific value and environmental friendliness.As a zero-emission and high-purity hydrogen production technology,hydrogen production through water electrolysis can get rid of the dependence on fossil fuels fundamentally and avoid environmental pollution problems at the same time.However,due to the lack of non-noble metal catalysts with high catalytic performance and low cost,the development and application of large-scale water splitting technology have been greatly hindered.Therefore,it is crucial to find an efficient and cheap electrocatalyst to accelerate the slow kinetics of anodic oxygen evolution(OER)and cathodic hydrogen evolution(HER)reactions and avoid unnecessary energy consumption.In this thesis,based on the hollow nanostructure with MoSe2 and Mo2C as the main active components,a series of high efficiency HER electrocatalysts were successfully synthesized through simple hydrothermal,high-temperature selenization or carbonization processes,and the material characterization and electrochemical performance were performed in detail.Specific research contents and results are as follows:(1)In the first part,we synthesized MoSe2/C hollow nanostructure through simple self-templated synthesis and high-temperature selenization process,and characterized its morphology,structure,composition and valence state in detail.Firstly,the crystallinity of MoSe2 and the graphitization degree of carbon components were optimized by controlling the selenization temperature.Electrochemical tests show that the catalytic performance of the electrocatalysts improved with the increase of selenization temperature.MoSe2/C-900℃ with the calcination temperature of 900℃ shows the best performance:MoSe2/C-900℃ possess a relatively low overpotential of 180 mV at a current density 10 mA cm-2,a Tafel slope of 85 mV dec-1,and a double layer capacitance of 25.1 mF cm-2(much higher than that of MoSe2/C-700℃(13.4 mF cm-2)).Secondly,the electrocatalytic performance of MoSe2/C with hollow structure is far better than that of MoSe2/C with block MoSe2/C obtained by direct selenization from Mo-G,which indicates that hollow nanostructure plays an important role in improving the electrocatalytic performance of HER.(2)In the second part,we prepared multi-step cobalt modified Mo2C hollow spheres(CMCHSs)as hydrogen evolution electrocatalysts by an efficient multi-step strategy,and carried out detailed morphology and structure characterization and electrochemical test.Firstly,Mo2C crystallinity and graphitization degree of carbon components are adjusted by carbonization temperature,so as to achieve effective regulation of the catalytic performance of materials.The overpotential of Mo2C/C-800℃ is 157 mV at a current density 10 mA cm-2,which is obviously better than that of Mo2C/C-600℃and Mo2C/C-900℃.Secondly,the HER performance is further improved by surface regulation of cobalt species.CMCHSs has the most outstanding performance:CMCHSs possess a low overpotential of 139 mV at a current density 10 mA cm-2,a Tafel slope of 86 mV dec-1,and a double layer capacitance of 18.11 mF cm-2(much higher than that of MCHSs(5.1 mF cm-2)),suggesting that the HER performance of CMCHSs increases significantly after surface regulation of cobalt species.