A Study On High Pressure Synthesis Of Metal Sulfides And Their Properties

Hydrogen,as a sustainable,clean energy carrier with high gravimetric energy density,has received much attention.Electrocatalytic and photoelectrocatalytic water splitting are important pathways of hydrogen production.Owning to their exciting electrochemical and optoelectronic properties,metal sulfides have been regarded as representative materials of water splitting for HER.Recently,the demand of high-performance electrocatalysts has greatly promoted the development of synthesis technology of metal sulfides and their composites.However,it should be pointed out that most preparative techniques of metal sulfides need a steady flow of the S sources.Moreover,the S sources are normally uncontrollable.Therefore,to increase utilizing ratio and effective control of the S sources,metal sulfides were synthesized under high pressure in a closed reactor.Further,nanostructured molybdenum disulfide(MoS2)and Co-doped MoS2 were synthesized for highly efficient HER process and the electrochemical performance for HER was characterized.In this work,different Mo and S sources were used to synthesize MoS2.The influence of reaction sources(the Mo and S sources),and temperature(reaction temperature,heating rate and holding time)on morphology and structure was investigated.MoS2 nanoflakes on Mo spheres,pistil-like MoS2,vertical MoS2 nanosheet coated Mo O2 block,spherical MoS2,MoS2 particle,MoS2 nanoflakes grown from Mo O2 nanorod,MoS2 film,plate-like MoS2 and randomly oriented MoS2 nanosheet were synthesized by using sulfur powder as the S sources and microscale Mo,nanoscale Mo,Mo O3,Mo(CO)6,(NH4)6Mo7O24?x H2 O,Mo O3,Mo Cl5,(NH4)2Mo S4 and H3P(Mo3O10)4?x H2 O powders as the Mo sources,respectively.MoS2 nanoflakes with network structure and MoS2/Mo O2 hybrid nanosheets were synthesized by using H3P(Mo3O10)4?x H2 O as the Mo sources,and(NH2)2CS and(NH4)2S2O3 as the S sources,respectively.The enhanced crystallinity of the MoS2 can be achieved as the reaction temperature and holding time increased,heating rate decreased when H3P(Mo3O10)4?x H2 O and S powder were used as the Mo and S sources,respectively.Subsequently,the electrochemical performance for HER of MoS2 was characterized.We found that the morphology of MoS2 has significant influence on their catalytic activity.The HER activity can be enhanced by synthesizing smaller-size MoS2 nanosheets owing to more abundant exposed active sites.To improve the catalytic activity of MoS2,the influence of Co dopant on morphology,structure and the HER electrocatalytic activity was investigated.The results demonstrate that Co-doped MoS2 nanosheets were obtained when weight ratios of cobalt acetate and phosphomolybdic acid were 1.0%,5.0%,10%,20% and 40%,respectively.In addition,with the progressively increased Co dopants,the electrocatalytic activity of Co-doped MoS2 nanosheets was improved.However,MoS2/Co S2 hybrid was obtained when weight ratios of the cobalt acetate and phosphomolybdic acid were 50% and 100%.Only when the weight ratio of cobalt acetate and phosphomolybdic acid was 40%,and the reaction temperature were 600 °C and 700 °C,the branched Co-doped MoS2 nanosheets can be synthesized,which exhibited superior HER performance and extraordinary catalytic stability.The excellent HER performance may be attributed to the synergistic effect between Co atom and MoS2.