| Excessive use of fossil fuels has exacerbated environmental issues such as air pollution and global warming.Therefore,the development of a clean and renewable energy to replace fossil fuel has become increasingly urgent.In the strategic research of developing various alternative energy sources,building an energy infrastructure with hydrogen as the main carrier and providing cheap and clean energy will become the direction of people's efforts in the future.Because water is a rich and renewable source of hydrogen,electrolyzed water provides hope for sustainable hydrogen production,providing technical support for the regeneration of hydrogen energy.However,the high cost of electrolyzed water limits the industrialization of this technology application.At present,commercial hydrogen-making electrocatalysts are mainly noble metals such as platinum(Pt),and the development of non-precious metal high-efficiency electrocatalysts composed of abundant elements on the earth will significantly reduce the cost of electrocatalysis.In recent years,researchers have developed non-precious metal catalysts with excellent performance through breakthroughs in nanoscience and nanotechnology,and have achieved fruitful results.Among them,molybdenum disulfide material is the most representative one of transition metal sulfides.Due to its unique layer structure and electrochemical activity,its application in the field of electrocatalytic water decomposition has received widely concerned.However,there are still some problems in the current molybdenum disulfide electrocatalyst:(1)the base surface is inactive,only the edge has electrocatalytic activity,and it is necessary to increase the active surface area;(2)the intrinsic catalytic activity site is less,and it needs to introduce more defects and other active sites;(3)poor conductivity,need to promote interface charge transfer and so on.In view of these shortcomings,this paper mainly studies the preparation of nano-molybdenum disulfide electrocatalyst by hydrothermal method,and further increases the active surface area,increases the number of active sites and enhances the conductivity of molybdenum disulfide by compounding with carbon and nitrogen materials,thereby enhancing its electrocatalytic hydrogen evolution performance.The main research contents are as follows:1.The ammonium molybdate tetrahydrate,thioacetamide and the fired graphite phase carbonitride(g-C3N4)were dispersed together in water,and the high temperature and high pressure reaction was carried out in a hydrothermal reaction kettle to synthesize g-C3N4/MoS2 composite.The catalyst was investigated and characterized by its morphology and electrocatalytic hydrogen evolution performance.The similarity of the layered structure between MoS2 and g-C3N4 has a positive effect on charge transfer and promotes the electrocatalytic hydrogen evolution reaction.Compared with pure MoS2,the nanostructure of g-C3N4/MoS2 composite catalyst has higher electrocatalytic hydrogen evolution performance.With the increase of g-C3N4 percentage,the electrocatalytic activity of MoS2 is optimized.When the content of g-C3N4 is 12.5%(wt%),the electrocatalytic performance is optimal.When the current density is-10 mA·cm-2,the overpotential is only 268 mV,and the Tafel slope is 61.5 mV·dec-1.Continue to add the content of g-C3N4,and the hydrogen evolution performance will decrease.Therefore,adding appropriate amount of g-C3N4 can enhance the electrocatalytic activity of molybdenum disulfide and has good stability.2.An ammonium intercalated molybdenum disulfide nanoelectrocatalyst was prepared by a simple hydrothermal method.After intercalation with ammonium,the interlayer spacing of molybdenum disulfide increases,and increases density of catalytically active sites,and promotes charge transfer and exhibits excellent electrocatalytic hydrogen evolution reaction activity.The electrochemical test results show that the ammonium intercalation MoS2 synthesized by adding proper amount(3 mL)of ammonia water has excellent electrocatalytic hydrogen evolution performance,and the overpotential at-10 mA·cm-2 is reduced from 388 mV of pure MoS2 to 278.mV,the Tafel slope is also reduced from 118 mV-dec-1 to 62 mV·dec-1,and the electrocatalytic hydrogen evolution performance is significantly improved.In addition,the ammonium intercalation layer can also improve the electrochemical hydrogen production stability of the MoS2 catalyst.3.The micro-nitrogen-doped carbon(NC)nanoparticles were successfully modified on the surface of MoS2 by simple sintering of the surface carbonization strategy of MoS2 microspheres and dicyandiamide(DCDA).In the process of electrocatalytic hydrogen evolution,the presence of NC on MoS2 facilitates charge transfer and accelerates the reaction rate,so that the catalyst has lower overpotential and higher current density than the pure MoS2,and improves the long-term electrochemical stability.The experimental results showed that when the MoS2:DCDA mass ratio was 1:1,the electrocatalytic activity reached the optimal value,and the overpotential at-10 mA·cm-2 was 310.6 mV,which was far less than 384.6 mV of the pure MoS2 microsphere.The taffele slope decreased from 193 mV·dec-1 to 135 mV·dec-1.In addition,the NC-modified MoS2 electrocatalyst can undergo electrocatalytic hydrogen evolution reaction under acidic and alkaline conditions,and the hydrogen evolution performance is better under alkaline conditions. |
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