Preparation Of N-doped Mo_xC/CoP Composites And Study On The Hydrogen Evolution Performance Of Electrolyzed Water

Hydrogen is considered to be the most promising new energy due to its advantagessuch as green,renewable and high energy density.Hydrogen evolution reaction（HER）of electrolyzed water technology has attracted widespread attention due to its high product purity and environmental friendliness,but it has the problem of large reaction energy consumption.Therefore,how to reduce the overpotential of hydrogen evolution has become the focus of research on efficiency hydrogen production by electrolysis water.Platinum-like noble metals are the most excellent HER catalysts at present,but problems such as high price limit their large-scale applications.Transition metal catalysts with nanostructures have strong binding force to hydrogen and are cheap,so they are expected to become alternative materials for platinum-like noble metals.In this thesis,the CoP catalyst is modified by non-metallic N elements and Mo₂C to improve its hydrogen evolution performance.First,nano-CoP materials were prepared,and then hollow Mo₂C nanotubes were synthesized by organic-inorganic hybrid template assisted strategy using MoO₃ nanowires as template,and N doping was performed on it to gain N-Mo_xC.Finally,N-Mo_xC and CoP are compounded to obtain N-Mo_xC/CoP catalyst.X-ray diffraction（XRD）,Raman spectroscopy,infrared spectroscopy（FTIR）,specific surface area and pore size distribution and scanning electron microscopy（SEM）were used to characterize the structure,purity and morphology of the products,and the electrochemical hydrogen evolution performance of the samples was tested.The main research contents are as follows:（1）Nano-CoP catalysts were prepared by solution method combined with chemical vapor deposition,and the effects of raw materials ratio,phosphating temperature and time on the synthesis of materials were optimized.It was determined that the CoP synthesized at the molar ratio of cobalt nitrate hexahydrate to 2-methyl imidazole of1:5,the phosphating temperature of 350℃and the phosphating time of 1.5 h was aggregated with 200～500 nm flake structures.Electrochemical test results showed that the overpotential(η₁₀)of CoP material to reach a current density of 10 m A cm^-2in the hydrogen evolution reaction was 141 m V and the Tafel slope was 66 m V dec^-1.（2）The MoO₃ nanowire template was successfully prepared by hydrothermal method.When the volume ratio of concentrated nitric acid to water in the reaction material was 1:7,the hydrothermal reaction temperature and reaction time were 200℃and 20 h,respectively,the synthesized MoO₃ nanowires had smooth surface and good dispersion,with a length of about 30μm and a diameter of 100～200 nm.Using the above MoO₃ nanowires as templates,Mo₂C nanotubes were synthesized by organo-inorganic hybrid template assisted strategy,and the molar ratio of ammonium molybdate tetrahydrate to dopamine hydrochloride,reaction temperature,reaction time and pH of reaction solution in the preparation process were optimized.The inner diameter and wall thickness of Mo₂C nanotubes are about 150 nm and 100 nm,respectively.The tube wall is assembled by two-dimensional ultra-thin nanosheets with a thickness of about 10 nm and the grain size of the nanosheet is about 2 nm.The BET specific surface area of the material is 140 m² g^-1.The performance test results showed that the Mo₂C NTs has aη₁₀ of 138 m V,a Tafel slope of 69 m V dec^-1,and a double layer capacitance value of 18.820 m F cm^-2.（3）The Mo₂C synthesized in（2）was doped with N to prepare N-Mo_xC through chemical vapor deposition,and the effects of the addition amount of nitrogen source（diammonium dicyanide）,reaction temperature and time on the synthesis of the catalyst were studied.When the mass ratio of Mo₂C to diammonium dicanide is 1:10,the reaction temperature and time were 700℃and 2.0 h,respectively,the specific surface area of the synthesized N-Mo_xC increased to 189 m² g^-1(Mo₂C:140 m² g^-1),and the hydrogen evolution overpotentialη₁₀ decreased to 120 m V（Mo₂C:138 m V）,which has stronger catalytic activity.（4）N-Mo_xC/CoP composites materials were prepared on the basis of（1）and（3）,and the influence of the addition amount of N-Mo_xC and CoP on the hydrogen evolution performance of N-Mo_xC/CoP were investigated.The results show that when the mass ratio of N-Mo_xC to CoP is 0.5,the catalytic activity of the synthesized N-Mo_xC/CoP atη₁₀ is 106 m V,which is higher than that of CoP（141 m V）,Mo₂C（138 m V）and N-Mo_xC（120 m V）.The Tafel slope value of 59 m V dec^-1 is similar to that of commercial Pt/C(54 m V dec^-1),and it can work in alkaline electrolyte for more than 30 hours,so N-Mo_xC/CoP has good HER reactivity and stability.