Controllable Synthesis Of Ruthenium-base Nanomaterials And Their Application For Electrocatalytic Hydrogen Evolution Reaction

The increasingly serious environmental pollution and energy shortage caused by the rapid consumption of fossil fuels have seriously affected people's life and survival,and the development and utilization of eco-friendly and renewable energy sources is urgent.Nevertheless,the discontinuity of these renewable energy sources such as solar and wind energy in time and space leads to the application obstacles.The electricity produced by the renewable energy is converted into hydrogen with high energy density by electrolysis of water,which is the effective way to solve this problem.Compared with the traditional hydrogen production methods,electrocatalytic water splitting is an efficient and eco-friendly way for large-scale production of high-purity hydrogen.Although the theoretical thermodynamic potential for water splitting is 1.23 V,practically,a much higher voltage than the theoretical value is required to drive water splitting at a satisfied reaction rate.High-efficiency cathode electrocatalysts can effectively improve the sluggish kinetics during the water electrolysis process,reduce the overpotential,and achieve the purpose of reducing energy consumption and enhancing energy conversion efficiency.Although Pt-based electrocatalysts have excellent cathodic hydrogen evolution recation(HER)activity,the scarcity,high price and poor stability are limit their actual application.Therefore,it is necessary to design and construct the HER electrocatalysts with high performance,excellent durability and low cost in large-scale sustainable hydrogen production.In recent years,electrospinning-based nanomaterials have been widely used in the field of electrocatalytic HER due to their inherent advantages such as large surface area,light weight,good electrical conductivity,high chemical stability,easy-to-adjust components and porosity.Meanwhile,considering the flexible diversity of metal-organic framework(MOFs)materials,we designed and synthesized a series of HER electrocatalysts with excellent activity and stability based on electrospinning technology or MOFs materials or combination of them by adjusting material composition,controlling morphology and manufacturing hierarchical porous structure.The main contents of this thesis are as follows:1.Ru-Mo/PVP(PVP = polyvinylpyrrolidone)composite nanofibers containing Ru and Mo ions were synthesized by electrospinning method,then a series of N-doped carbon nanorods with multi-active components(Ru-RuO₂/MoO₃ CNRs)were prepared by pyrolysis the composite nanofibers in air.Thanks to the synergistic effects between Ru and Mo components,large electrochemical surface area,and high electrical conductivity,Ru-RuO₂/MoO₃-350 CNRs display excellent HER activity in alkaline electrolyte.The optimal electrocatalyst only needs ultralow overpotential of 9.2 m V to drive the current density of 10 m A cm^-2,which is comparable to commercial Pt/C,and even superior to it at the higher current densities.In addition,the ratio of Ru and RuO₂ in the electrocatalysts was tuned by controlling the pyrolysis temperature(250-400 ?).It was found that the proper ratio of metal/metal oxide was beneficial to improve the conductivity of the electrocatalyst,accelerate the electron transfer,and thereby improve the catalytic activity of the material.2.Zeolitic imidazole framework(ZIF-8)and Ru³⁺ ions were encapsulated into nanofibers by simple electrospinning technique.N-doped carbon nanofibers(ES-Ru-ZIF-900)with hierarchical porous structure and uniform dispersion of small-size Ru nanoparticles(⁸ nm)were prepared by high temperature carbonization.The uniformly dispersed Ru nanoparticles provide abundant active sites,the highly conductive N-doped carbon matrix ensures efficient and rapid electron transfer,and the porous structure with high specific surface area improves the exposure of active sites and accelerates the penetration of electrolytes.As a result,the prepared electrocatalyst ES-Ru-ZIF-900 exhibit better catalytic activity than Pt/C and other noble-based electrocatalysts in the alkaline electrolyte.3.The RuCo(OH)x@ZIF-67 derivate with core-shelled structure were generated by simultaneous hydrolysis and co-precipitation of ZIF-67 templates in the mixed water/alcohol system containing RuCl₃.Ru-Co oxides/Co₃O₄ double-shelled hollow polyhedrons(RCO/Co₃O₄-350 DSHPs)with Ru-Co oxides as an outer shell and Co₃O₄ as an inner shell by pyrolysis of core-shelled structured Ru Co(OH)x@ZIF-67 derivate at 350 °C were constructed.The unique double-shelled hollow structure provides the large active surface area with rich exposure spaces for the penetration/diffusion of active species and the heterogeneous interface in Ru-Co oxides benefits for electron transfer,simultaneously accelerating the subsequent surface electrochemical reactions.The theory computation further indicates that the existence of heterointerface in RCO/Co₃O₄-350 DSHPs optimize the electronic configuration and further weaken the energy barrier in the HER process,promote the catalytic activity.As a result,the obtained RCO/Co₃O₄-350 DSHPs exhibit outstanding HER performance with a low overpotential of 21 m V at 10 m A cm^-2,small Tafel slope of 67 m V dec^-1,and robust stability in 1.0 M KOH.This synthesis strategy opens new avenues for designing transition metal oxides with the special structure in electrochemical applications.