Preparation Of Mn And Co-based Electrochemical Catalytic Materials And Their Performance Of Water Splitting

The environmental crisis brought about by the energy crisis and the burning of fossil fuels is getting worse.These imminent problems urgently need us to think and solve.As a renewable energy source,the biggest advantage of hydrogen is its high calorific value and zero pollution to the environment.Therefore,hydrogen energy has attracted widespread attention.Electrochemically water splitting can produce hydrogen.The process of using electrochemically water splitting is safe,simple in equipment,and highly efficient.The process of electrochemically water splitting includes two half reactions:the oxygen evolution reaction（Oxygen evolution reaction）of the anode is referred to as OER,and the hydrogen evolution reaction（hydrogen evolution reaction）of the cathode is referred to as HER.Theoretically,water splitting to produce hydrogen requires a voltage of 1.23 V to complete.However,the oxygen evolution reaction occurring at the anode involves the transfer of four electrons in the entire water splitting process and requires a large amount of electrical energy.In order to effectively improve the problem of excessive overpotential in the process of water splitting,there is an urgent need to design and manufacture excellent electrode catalytic materials.In the hydrogen evolution stage,the best performing catalytic material is a Pt-based material,while in the oxygen evolution stage,the best performing material is an Ir/Ru-based material.However,their scarce content and poor stability in the earth’s crust have prevented their use in production and life.The development of cheap,efficient and stable non-precious metal materials to replace traditional precious metal materials is of paramount importance.Starting from this perspective,a series of catalytic materials were prepared and developed based on the rich Mn and Co in the crust as the basis of non-precious metal catalysts.The prepared materials were tested using materials characterization and electrochemical testing methods.Aiming at the different types and structures of catalytic materials,the factors affecting their performance are analyzed in detail.First,MnCo₂S₄ electrochemical catalyst material for full hydrolysis was prepared by hydrothermal method and sulfidation method.Bimetallic sulfides strengthen the connection between atoms,increase surface active sites,and accelerate the transfer efficiency between electrons.In the OER stage,in 1.0 M KOH,in order to achieve a current density of 50 mA cm^-2,a voltage of 1.54 V needs to be applied to MnCo₂S₄/NF,that is,an overpotential of 310mV.In the HER phase,at a current density of 10 mA cm^-2,the overpotential is 167 mV.When the two-electrode catalyst system composed of MnCo₂S₄/NF is used to water splitting,in 1.0 M KOH,a voltage of 1.60 V is required to reach 10 mA cm^-2.Moreover,the MnCo₂S₄/NF catalyst exhibited good stability.The current density of the catalyst after 14hours of continuous operation remained around 10 mA cm^-2.Secondly,CuCo₂S₄@Ni（OH）₂ composites were prepared by using artificially induced oxygen vacancies and a combination of hydrothermal and electrochemical deposition methods.Compared with the traditional coating adhesion,the electrochemical deposition catalyst has a better synergistic effect with CuCo₂S₄ and Ni（OH）₂.This catalytic material not only improves the electron transfer rate,but also builds an O-S interface between the catalyst’s interiors,making CuCo₂S₄@Ni（OH）₂/NF more active.What impresses us is that it requires an extremely low battery voltage of 1.47 V to provide a current density of 10 mA cm^-2 for electrocatalytic water splitting in alkaline electrolytic cells.Finally,in order to optimize the structure of the catalytic material,control the synthesis of MnCo oxide structure,and cooperate with the good catalytic effect of Ni₃S₂ to prepare MnCo₂O₄@Ni₃S₂ nanocomposite structural materials.Utilizing the Mn²⁺,Mn³⁺multiple redox states,Co²⁺,Co³⁺multiple redox states in the catalytic material,and the synergy between the bimetals,the electrochemical performance is further improved.The catalytic material showed stable electrochemical activity during a 12-hour stability test.In this thesis,by designing and optimizing the structure of inorganic non-precious metal materials,we explore the intrinsic factors of each material to improve the electrocatalytic activity.The prepared materials exhibit different catalytic properties in the processes of oxygen evolution reaction,hydrogen evolution reaction and total water splitting reaction,which provides new ideas and methods for the development of clean energy catalytic materials.