Molybdenum Phosphide-based Nanomaterials:Synthesis And Electrocatalytic Hydrogen Evolution Properties

With the carbon emission from burning fossil fuels such as coal and oil,the environmental pollution is becoming more and more serious.Hydrogen is one of the most promising energy carriers because of its clean combustion products and high energy density.The preparation of hydrogen by electrolysis of water has been recognized as an effective method.At present,platinum(Pt)and other noble metal catalysts are widely used as catalyst materials in hydrogen production process by electrolysis because of their high efficiency.Considering the low earth reserves and high preparation cost of precious metals,it is of great practical value to develop non-precious metal electrolytic water catalysts with cost-effectiveness and high performance.Molybdenum phosphide(MoxPy)has the advantages of similar electronic structure to platinum,high catalytic activity and low cost,so it has a broad prospect in electrocatalytic hydrogen evolution catalysis.The catalytic efficiency is still much lower than that of PT because of the lack of active sites and poor conductivity.Aiming at the above shortcomings of MoxPy,the preparation,structure control and electrochemical performance of MoxPy-based composite nanomaterials were studied in order to obtain higher efficient hydrogen evolution catalyst for electrolyzing water.The results of the researches are as follows:(1)CoP-Mo3P composite nanomaterial was prepared on carbon cloth(CC)substrate by hydrothermal method and phosphating treatment.The introduction of CC with good conductivity avoids the use of polymer binder and reduces the series resistance of CoP-Mo3P/CC composites.At the same time,the synergistic effect of Mo and Co atoms improves the electrical properties of the composite.Compared with pure Mo3P,only 150 mV overpotential is needed for the current density of 10 mA·cm-2 in 1 M KOH medium,and the Tafel slope is 78.1 mV·dec-1,which shows excellent electrocatalytic activity.At the same time,after 1000 cycles,the overpotential has little change,with long-term stability.(2)Ni2P-MoP2 composite nanomaterial was grown on the nickel foam(NF)substrate.The three-dimensional network structure of NF makes the composite have larger electrochemical active surface area.The composite of Ni2P and MoP2 reduces the charge transfer resistance of the composite and accelerates the mass transfer process.Compared with MoP2,the Ni2P-MoP2 composite nanomaterial has higher catalytic activity for hydrogen evolution:at current density of 10 mA·cm-2,the overpotential is 96 mV,and the Tafel slope is 77.8 mV·dec-1.(3)The Ni2P-MoNiP2 heterostructure nanosheet arrays(HNSAs)were prepared by high temperature phosphating treatment using a CC-loaded NiS-MoS2(HNSAs)as a template.The current density of 10 mA·cm-2 in 0.5 M H2SO4 medium needs only 74 mV overpotential,and the s Tafel slope is 63 mV·dec-1,which is mainly attributed to the synergistic effect of Ni2P and MoNiP2,at the same time,the introduction of carbon cloth improved the conductivity of the composite material and accelerated the mass transfer of charge.The water electrolysis hydrogen cathode made of the electrode material showed good stability and durability.