Preparation And Electrocatalytic Hydrogen Evolution Of Carbon Supported Molybdenum Sulfide Catalysts

With the increasing global fossil energy crisis and environmental pollution problem,hydrogen energy as a clean and renewable green energy attracts much attention.Electrolysis water is an effective method for hydrogen production,however,high cost noble metal platinum has limited its application.Therefore,research and development of low cost and high activity no-noble metal electrocatalysts is of great significance.Molybdenum sulfide nanomaterials are considered as promising catalysts for the hydrogen evolution instead of noble metal platinum.However,molybdenum sulfide has the defects of poor conductivity,easy agglomeration and small specific surface area,which limits the catalytic performance.In this paper,a carbon loaded molybdenum sulfide nanomaterial was prepared via one step hydrothermal method.The conductivity and specific surface area of molybdenum sulfide have been remarkably improved.The effects of preparation conditions and loading ratio on the performance of electrocatalytic hydrogen evolution have been studied.Firstly,MoSx/C was prepared by hydrothermal method of ammonium molybdate and thiourea using carbon black(Vulcan-72)as the carrier.The results show that the fully exposed amorphous molybdenum sulfide(MoSx)as the active site,the micromorphology is spherical(100-200 nm in diameter)and the specific surface area is 115.5 m2/g.The combination of carbon black and molybdenum sulfide not only improves the conductivity,but also induces the growth of molybdenum sulfide nanoflakes on the edge of carbon black nanospheres,forming rich bare edges and increasing the specific surface area.The electrochemical results show that when the hydrothermal temperature is 200℃,the reaction time is 10h and the preload was 200%,the electrocatalytic performance of MoSx/C is the best.Hydrogen evolution potential is-145 mV(VS.RHE),the over potential is-208 mV(vs.RHE)at the current density of 10 mA/cm2,and the reaction resistance is 60.08 Ω.The mechanism study shows that the Tafel slope of the MoSx/C is 44 mV/dec,which conforms to the reaction mechanism of Heyrovsk-Volmer,and the speed control step is Heyrovsk reaction.Secondly,MoSx/GO was prepared via the same method using graphene oxide as carrier.The results show that molybdenum sulfide is mainly distributed in the defect location of graphene oxide,with a diameter of about 100 nm and a specific surface area of 173.1 m2/g.Functional groups on graphene oxide provide attachment points for the growth of molybdenum sulfide.Under the same preload(100%),the effective load of MoSx/GO is two times for MoSx/C,and the loading efficiency is significantly improved.The electrochemical results show that when the hydrothermal temperature is 200℃,the reaction time is 10h and the preload was 100%,MoSx/GO has an approximate hydrogen evolution performance to MoSx/C.The hydrogen overpotential is-207 mV(vs.RHE)at the current density of 10 mA/cm2 and the reaction resistance has been greatly reduced(37 Ω).The mechanism study shows that the Tafel slope of MoSx/GO is 33 mV/dec,which conforms to the reaction mechanism of Tafel-Volmer and the speed control step is Tafel reaction.Finally,NHPC was prepared by high temperature activation of cattle bone and MoSx/NHPC was prepared by compositing molybdenum sulfide and NHPC.The results show that molybdenum sulfide is highly dispersed on the surface of NHPC,with a particle size of 2-10 nm and a high specific surface area(655.9 m2/g).The electrochemical results show that the hydrogen overpotential of MoSx/NHPC is-206 mV(vs.RHE)at the current density of 10 mA/cm2.The Tafel slope is 46 mV/dec,which conforms to the reaction mechanism of Heyrovsk-Volmer,and the speed control step is Heyrovsk reaction.The unique microstructure and nitrogen doping advantages of NHPC provide abundant growth sites for molybdenum sulfide,which effectively improve the preparation efficiency and reduce the cost of preparation.