Preparation And Regulation Of Transition Metal Based Catalysts And Their Application In Hydrogen Production From Water Electrolysis

Hydrogen is considered as an ideal alternative fuel to fossil energy due to its renewable nature and highest energy density,and sustainable hydrogen production is a necessary prerequisite for a future hydrogen economy.Electrolysis of water splitting by electricity generation from renewable sources and direct solar energy conversion of hydrogen based on photochemical methods are promising pathways for sustainable hydrogen production.However,these technologies often require highly active,non-precious metal catalysts to make the water splitting process more energy efficient and economical.Transition metals have received much attention in recent years due to their low prices,abundant reserves,and high catalytic activity.Accordingly,this thesis presents an in-depth and systematic study on the preparation,performance and application of three catalysts based on transition metal-based electrocatalysts.First of all,Co Fe LDH with oxygen vacancy defects was synthesized by nitrogen plasma etching,and the prepared V-Co Fe LDH was further modified by Ce doping,and V-Ce/Co Fe LDH required only 73 m V overpotential to reach 10 m A cm^-2.The etching process led to an increase in the number of reactive sites with more dangling bonds and lower coordination numbers in the catalyst,and the higher specific surface area brought.The increase in the number of reactive sites with higher specific surface area further leads to the rearrangement of electrons.Based on theoretical calculations and experimental results,the high hydrogen precipitation（HER）activity of V-Ce/Co Fe LDH stems from the synergistic effect of high electrochemical surface area（ECSA）,oxygen vacancies and enhanced electrical conductivity,which promotes the rapid charge transfer induced during the plasma etching process.With longer plasma etching time,both Co Fe LDH and Ce/Co Fe LDH tend to increase the lattice strain,and the strain introduced in Ce/Co Fe LDH is larger compared to Co Fe LDH.Therefore,it can be inferred that the plasma etching strategy not only induces vacancies and defects,but also leads to the conversion of the crystalline phase from Co Fe LDH to Co Fe₂O₄.Afterwards,β-Co（OH）₂ nanowires were prepared by hydrothermal Sn doping of Co₂（OH）₂CO₃ for its structural modulation.The results showed that the doping of Sn adjusted the electronic structure of Co（OH）₂ and improved the electrocatalytic active sites.Further,novel heterogeneous catalysts with Co/Co O/Co（OH）₂ nanowires with interfacial structure were synthesized by plasma etching method,which further enhanced the electrochemical specific surface area,tuned the electronic structure and improved the OER performance.The resulting catalyst exhibits an overpotential of 266m V at 20 m A cm^-2 in alkaline medium and has an ultra-long stability of more than 200hours.Further the catalyst was loaded onto Bi VO₄ photoanodes for solar-driven water splitting,showing enhanced photoelectrochemical（PEC）activity and stability.In the end,silver-doped Ni Fe LDH（Ag/Ni Fe LDH）was prepared by a one-step redox reaction through an atomic doping engineering strategy.The silver doping increases the intrinsic conductivity,enriches the active sites and improves the intrinsic surface area,and Ag/Ni Fe LDH exhibits excellent catalytic activity in large-scale applications.The results demonstrate the increase of Ag-O covalency and triggered lattice oxygenation,which does not lead to significant structural reconstruction.Experimental and theoretical calculations show that Ag doping enhances the phase stability of Ni Fe LDH and the exposed Ag acts as an active site by releasing-OH adsorbates.This work opens a viable strategy for the design of robust electrocatalysts and advances the development of seawater electrolysis for large-scale clean energy to achieve efficient and stable electrocatalysts for seawater oxidation at high current densities.