Study On Electrolytic Water Performance Of Transition Metal-based Catalysts Regulated By Non-metallic Elements

In recent years,with the increasing demand for energy,fossil fuels can not meet the needs of society.Environmental problems are also becoming more and more serious.This has stimulated the demand for renewable and clean energy.Hydrogen is an ideal candidate for future energy supply because of its environmental-friendly and sustainability.Electrochemical splitting of water is of great significance to realize hydrogen energy conversion and storage.The water splitting reaction is divided into two half reactions:hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）.The overpotential of HER and OER makes the actual electrolytic potential of water much higher than the theoretical value of 1.23 V.Therefore,it is necessary to find efficient and stable catalysts with low overpotential to ensure effective water splitting.In this regard,noble metals such as Pt and noble metal oxides such as Ru O₂ or Ir O₂ are used as high activity catalytic electrodes of HER and OER respectively.However,the high cost and low reserves of noble metal greatly limit its wide application.Transition metals have a unique electronic configuration,so they have high potential catalytic activity.In addition,compared with noble metal,transition metals have higher abundance and cheaper price.In this thesis,a series of transition metal-based nanomaterials with special morphology have been synthesized by introducing non-metallic elements to regulate transition metals and combining them with some base materials,such as carbon cloth and nickel foam.The specific research works are as follows:1.Selenium doped Co P were successfully synthesized on carbon cloth by hydrothermal route and one-step phosphoselenization.It shows high HER and OER catalytic activity and good stability in 1 M KOH,including low over potential(HER/OER over potential is 47 m V/232 m V and 143 m V/357 m V when the current density reaches 10 m A cm^-2 and 100 m A cm^-2,respectively),good reaction kinetics,large electrochemcial active surface area and small charge transfer resistance.This is mainly due to its special nanostructure and electron redistribution caused by Se doping.Considering its good catalytic activities of HER and OER in 1 M KOH solution,Se-Co P/CFC is used as cathode and anode to construct a double electrode system for overall water splitting.The results show that the overpotential is only 1.59 V when the current density reaches 10 m A cm^-2.Non-metallic elements are introduced to regulate transition metal-based catalysts,which makes a promising and feasible attempt to explore and design efficient electrolytic water catalysts.2.Ni₂P-NiMoP₈ composites loaded on nickel foam are successfully synthesized with hydrothermal method and simple phosphorization.HER catalytic activity of the synthesized Ni₂P-NiMoP₈/NF is slightly improved.Ni₂P-NiMoP₈/NF displays high catalytic activity of OER and good stability.Internal low overpotential(the current density reaches 100 m A cm^-2 when the overpotential is 243 m V and 310 m V in 1 M KOH solution and alkaline simulated seawater respectively)is obtained both in 1 M KOH solution and alkaline simulated seawater,as well as excellent reaction kinetics,large electrochemcial active surface area,small charge transfer resistance and good stability.It is worth noting that in 1 M KOH solution and alkaline simulated seawater solution,Ni₂P-NiMoP₈/NF achieves a high current density of 400 m A cm^-2 at an overpotential of 367 m V and 390 m V respectively,which is of great significance for overcoming one of the main challenges of seawater splitting（chlorine evolution reaction）.Finally,Ni₂P-NiMoP₈/NF is used as cathode and anode to form a double electrode system to electrolyze alkaline simulated seawater solution.When the current density reaches 10 m V cm^-2 and 100 m A cm^-2,the required battery voltage is 1.55 V and 1.84V respectively.This work makes an effort to explore and design transition metal-based phosphides electrocatalyst to realize water electrolysis and further seawater electrolysis.