Synthesis And Electrocatalytic Properties Of Metal Molybdate Nanomaterials

With the depletion of fossil energy and the worsening of environmental pollution,the development of renewable,clean,safe and efficient new energy sources has become particularly important.Among the many new energy sources that can be developed,hydrogen is considered to be an ideal alternative to fossil fuels due to its advantages of wide sources,high energy density,high conversion efficiency and no pollution from combustion products.Electrochemical water splitting provides a green and sustainable way to produce hydrogen.However,the sluggish kinetics of the oxygen evolution reaction?OER?at the anode greatly limits the water splitting procedure due to the involvement of a multistep four-electron oxidation process.Searching for efficient OER catalysts is very important for the current development of hydrogen production technology by electrolysis of water.Currently,precious metal oxides?such as Ir O₂ and Ru O₂?are the state-of-the-art OER catalysts,but their low abundance and high cost hinder their widespread use.Therefore,it is necessary to design and develop highly active OER catalysts made from earth-abundant elements.In recent decades,mixed metal oxides have become hot research topics in electrochemical fields due to their rich redox reactions and high electrical conductivity.Metal molybdates are complex in both nature and structure,which keeps them in a distinguished category of mixed metal oxides.To this end,we designed and prepared a series of metal molybdate nanomaterials and studied their catalytic performance of electrolyzed water.The main research contents are as follows:?1?Synthesis and electrocatalytic properties of FeMoO₄ nanorod arraysAmong the many metal molybdate,considering that iron?Fe?is abundant element in the earth and has abundant oxidation valence states?+2,+3?,it has aroused our great research interest.In this study,we demonstrate the development of FeMoO₄ nanorod arrays on nickel foam?FeMoO₄/NF?via a facile hydrothermal process.The nanoarray structure has a large specific surface area,which can provide more active sites during the catalytic reaction,resulting in enhanced electrocatalytic behavior of the material.We study the OER catalytic performance of FeMoO₄/NF through electrochemical testing techniques.The data show that the catalyst needs an overpotential of only 293 m V to drive a current density of 50 m A cm^-2 in 1.0 M KOH.In addition,this electrode also exhibits strong long-term durability for 80 h.These data indicate that FeMoO₄/NF is an excellent OER catalyst with superior performance due to the larger electrochemical active area and the bimetal synergy.The above research contents not only provide a new idea for the design of metal molybdate as an electrocatalyst,but also find a feasible method for finding new energy sources and solving environmental problems.?2?Synthesis and electrocatalytic properties of CaMoO₄ nanosheet arraysAs an important component of molybdate materials,calcium molybdate?CaMoO₄?has attracted extensive research interest because of its excellent physical and chemical properties.In addition,nanoarray structure can enhance the catalytic performance of the material.In this study,CaMoO₄ nanosheets grown on nickel foam?CaMoO₄/NF?have been successfully synthesized via a simple one-step hydrothermal method.Nickel foam has the characteristics of three-dimensional network structure,high porosity and large specific surface area,which not only increase the contact area between the electrode surface and the electrolyte,but also provide many fast and efficient transport channels for charges and electrolyte ions.The study found that CaMoO₄/NF has better catalytic performance than CaMoO₄/CC,which is mainly because the synythesized effect between CaMoO₄ nanosheets and nickel foam can effectively enhance the conductivity and stability of the electrode material.As a catalyst electrode for the OER,CaMoO₄/NF demands an overpotential of 345 m V to drive a geometrical current density of 50 m A cm^-2 in 1.0 M KOH.Notably,it also shows high long-term electrochemical durability for at least 25 h.This study has demonstrated the great potential of metal molybdate as OER catalys in alkaline media again.?3?Synthesis and electrocatalytic properties of Cu₃Mo₂O₉ nanosheet arraysAmong the many non-precious metals?Co,Ni,Fe,Cu,Mn?,Copper?Cu?is an abundant element in the earth's crust,which has less toxic and extensive redox properties similar to iron?Fe?.However,as one of the most common metallic elements,copper-based materials have been less studied in water electrolysis.In order to solve this problem,we have successfully prepared Cu₃Mo₂O₉/NF as an OER catalyst based on the inspiration of our previous work.We synthesized a series of copper-molybdenum-oxygen precursors by controlling the time of the hydrothermal method.Then,these precursors were annealed under argon atmosphere at the same temperature to obtain different copper-molybdenum oxides:Cu₃Mo₂O₉/NF-10h,Cu₃Mo₂O₉/NF-15h?Cu₃Mo₂O₉/NF?,Cu₃Mo₂O₉/NF-20h.These series of copper-molybdenum oxides all have OER activity in alkaline conditions.Cu₃Mo₂O₉/NF-15h?Cu₃Mo₂O₉/NF?exhibits a high activity for water oxidation and needs an overpotential of only 325 m V to drive a current density of 50 m A cm^-2 in 1.0M KOH.In addition,the electrode has a smaller impedance and good stability.The excellent catalytic performance of Cu₃Mo₂O₉/NF can be ascribed to the good conductivity,large electrochemical active area and the bimetal synergy.In conclusion,metal molybdate nanomaterials have excellent performances when work as OER catalysts,and provide a new idea for the development of renewable energy.