Preparation Of Molybdenum Disulfide,Molybdenum Phosphide/porous Carbon Materials And Their Efficient Hydrogen Evolution

The energy crisis and environmental pollution have severely restricted the development of society.Research and development of new renewable energy has become a key issue in the energy field.Hydrogen energy has the advantages of high energy density,abundant reserves,renewable,pollution-free,etc.And it is considered to be one of the most promising new energy sources to replace fossil fuels.Compared with the traditional hydrogen production technology,electrolyzed water production of hydrogen,with a large output and low energy consumption,is one of the effective ways to achieve sustainable development.Due to the scarcity and high cost of precious metal catalysts such as Pt,it is important to develop efficient and stable non-precious metal catalysts.MoS₂ and MoP have attracted more and more attention in the field of electrochemistry due to their rich reserves,high catalytic performance,and high stability.However,as a semiconductor,MoS₂ has poor conductivity and is easy to accumulate during the preparation process,which limits number of active sites and its electron transfer rate in the electrocatalytic hydrogen-evolution-reaction?HER?process.MoP as a hydrogen production electrocatalyst also has mainly insufficient active sites and poor conductivity problem.This dissertation has achieved high-performance HER electrocatalysts through preparing nitrogen-doped graphene-supported nanoscaled molybdenum disulfide?MoS₂/NGO?,aloe-derived reticulated carbon-supported nanoscaled molybdenum phosphide?MoP/CAJ?,and nitrogen-doped PPy-derived carbon-supported nanoscaled molybdenum phosphide?MoP/NPC?to overcome the intrinsical insufficient active sites and poor conductivity of MoS₂ and MoP.The results of the electrocatalytic hydrogen production performance test show that the MoS₂ and MoP-based catalysts prepared above have high activity and stability.The main research contents and results are as follows:?1?Using graphene oxide,dodecylmolybdophosphoric acid and thiourea as raw materials,ultra-thin MoS₂ nanosheets were grown in situ on nitrogen-doped graphene by a one-step hydrothermal method.The structure of the material was modified by adjusting the pH value of the reaction system.Introducing more defects and expanding interlayer spacing of MoS₂ can be achieved through decreasing the pH value of the reactive system.MoS2/NGO hybrids prepared at low pH exhibit superior HER activity to those obtained at high pH.It showed that MoS2/NGO-pH1.5 exhibits an ultralow overpotential of 81 mV at 10 mA·cm^-2,a low Tafel slope of 60 mV·dec^-1 and good stability in alkaline electrolyte.?2?MoP/CAJ composites with a three-dimensional network structure were synthesized by using aloe juice as a carbon precursor,absording a molybdenum compound after freeze-drying and pre-carbonizing treatment.Through the control of phosphation temperature and precursor amount,different phosphatized products were obtained.The results of electrochemical activity and stability testing of materials in acidic and alkaline electrolytes showed that MoP/CAJ-2 composite exhibit excellent electrocatalytic HER performance with smal overpotentials of 73mV and 211 mV at the current density of 10 mA·cm^-2,and low Tafel slopes of 58mV·dec^-1 and 79 mV·dec^-1 in 0.5 M H₂SO₄ and 1 M KOH solutions,respectively.?3?A polypyrrole?PPy?aerogel was prepared by an oxidative polymerization method,and a MoP/nitrogen-phosphorus co-doped carbon porous composite material was prepared by a high-temperature solid-phase method.Inheriting the porosity of polymer,the as-prepared material exhibits hierarchical porous microstructure with highly uniform dopants for improving the conductivity and mass transfer ability of the electrode material,and thereby improving the electrochemical HER performance of the material.And the anchored MoP on the carbon effectively reduce the agglomeration phenomenon of nanoscaled MoP,which leads to the improvement in long-term stability.The results show that MoP/NPC-2 composites exhibit excellent electrocatalytic hydrogen-production performance in both 0.5 M H₂SO₄ and 1 M KOH solutions with small overpotentials of 89 mV and 172 mV at a current density of 10 mA·cm^-2,and low Tafel slopes of 68 mV·dec^-1 and 66mV·dec^-1,respectively.