Fabrication Of Layered Molybdenum Disulfide Nanomaterials For Efficient Electrochemical Hydrogen Evolution Reaction

The growing consumption of fossil fuels?coal,oil,and natural gas?has caused serious air pollution and energy crisis.Hydrogen,as a clean and highly efficient energy source,has recently attracted enormous attention.Electrocatalytic hydrogen evolution reaction?H₂O?H₂+O₂?is an effective/efficient way to synthesize clean energy.However,due to the limited activity and stability of the catalyst,only 4%of hydrogen is produced by electrolyzing water for these years.Generally,platinum-based catalysts are exploited for electrocatalytic hydrogen evolution reaction because of their higher catalytic activity and lower polarization potential.However,scarcity and high cost of noble metal?Pt?prevent them practically being used on a large scale.Therefore,it is imperative to exploit a non-previous catalyst with excellent catalytic activity and electrochemical stability.As molybdenum disulfide has shown excellent performance in electrochemical hydrogen evolution,it has attracted widespread attention.This dissertation focuses on the further study of improve catalytic activity of molybdenum disulfide.The specific work is as follows:1.Molybdenum disulfide was hydrothermal synthesized using certain amount ofsodium molybdate,thiourea and silicon dioxide nanoparticles under the temperature of 200 ^oC.In this system,sodium molybdate and thiourea are exploited as as the molybdenum source,sulfur source,respectively.Then,the as-prepared molybdenum disulfide nanosphere were treated by NaOH to eliminate silicon dioxide nanoparticles.The performance of different morphology for electrochemical hydrogen evolution reaction has been evaluated.The results indicated that the overpotential of themolybdenum disulfide nanospheres reaches 310 mV at the current density of 10mA/cm²,and the overpotential of the flake-like molybdenum disulfide is much larger than 500 mV.The tafel slope of molybdenum disulfide nanospheres is 62 mV/dec,which is much smaller than 87 mV/dec for flake-like molybdenum disulfide.At the same time,molybdenum disulfide nanospheres has a larger electrochemical active surface area,causing more active sites and higher hydrogen evolution efficiency.2.Different structures of molybdenum disulfide were hydrothermal synthesized using certain amount of sodium molybdate,thiourea and silicon dioxide nanoparticles under different temperatures.In this system,sodium molybdate and thiourea are exploited as the molybdenum source,sulfur source,respectively.Then silicon dioxide nanoparticles were treated by NaOH and HF.The performance of different morphology and structure for electrochemical hydrogen evolution reaction has been evaluated.The result shows that some O atoms were doped in molybdenum disulfide at low hydrothermal temperature.Then increases the degree of disorder,generates more unsaturated Mo and S atoms,and increases the number of active sites.The oxygen-doped structure was destroyed by treating withHF.The oxygen-doped structure was retained by treating with NaOH.Molybdenum disulfide were disperse into independent paticles by the addition of silicon dioxide nanoparticles.Thus,increased the active area and the efficiency of hydrogen evolution.The overpotential of molybdenum disulfide prepared under 160 ^oC treated by NaOH reached 255 mV,and the Tafel slope was as low as 45 mV/dec.Therefore,it displays the best performance.3.The organics intercalated molybdenum disulfide was synthesized at 230 ^oC by hydrothermal method.Sodium molybdate,thiourea and ascorbic acid were exploited as the molybdenum source,sulfur source and carbon source,respectively.Then the as-prepared organics intercalated molybdenum disulfide nanomaterial was calcined to produce nanocarbon intercalated molybdenum disulfide hybrid.Carbon material is uniformly inserted into the layers of molybdenum disulfide.The intercalation of carbon improved and enhanced the conductivity and catalytic activity of molybdenum disulfide.The overpotential is only 195 mV and the tafel slope reaches 47 mV/dec at the current density of 10 mA/cm²,showing a highly efficient hydrogen evolution activity.