Study On Two-dimensional Materials And Their Nanocomposites Supported Noble Metal Electrocatalysts For Hydrogen Evolution Reaction

Global energy demand keeps growing due to the economic development and the progress of science and technology.The hydrogen is expected to become a candidate energy source for replacing fossil fuels because of its unique advantages such as high gravimetric energy density and zero carbon emi ssions.The technology of hydrogen production by water electrolysis is therefore widely concerned by people.Noble metal catalysts are considered as the most excellent electrocatalysts for hydrogen evolution reaction at present,but they still have the problems of high cost and low reserve.Therefore,reducing the use of noble metals by loading noble metals on the carrier and improving the electrocatalytic activity through carrier-metal interaction are promising methods for the study of electrocatalysts for hydrogen evolution.Two-dimensional（2D）materials are ideal for supporting noble metal due to their high specific surface area,anisotropic physical and electronic properties.In this thesis,taking two-dimensional materials（graphene,siloxene）and thei r nanocomposites as catalyst supports,three kinds of electrocatalysts for hydrogen evolution with low loading mass of noble metal have been developed.The specific works are as follows:（1）Using chloroplatinic acid,carbon nanotubes and graphene oxide as precursors,and ethylene glycol as solvent and reducing agent,we prepared carbon nanotubes/reduced graphene oxide composites loaded with Pt nanoparticles（Pt NPs/CNT-rGO）by hydrothermal method.The morphology and microstructure of the materials were characterized by scanning electron microscope（SEM）,transmission electron microscope（TEM）and X-ray diffractometer（XRD）.X-ray photoelectron spectroscopy（XPS）was used to analyze the chemical composition of the samples.The functional groups of the samples were characterized by Fourier transform infrared spectroscopy（FT-IR）.The content of the noble metal in catalyst was measured by inductively coupled plasma optical emission spectrometer（ICP-OES）.Linear sweep voltammetry（LSV）and cyclic voltammetry（C V）were used to investigate the electrocatalytic performance of Pt NPs/CNT-rGO for hydrogen evolution reaction.The results show that the Pt content of Pt NPs/CNT-rGO is 3.2wt%,η₁₀ is only 28 m V in 0.5 M H₂SO₄ medium,and the Taffel slope is 25.3m V×dec^-1,which shows a better mass specific activity than that of commercial Pt/C.Furthermore,the electrocatalytic activity is maintained well after 1000 CV cycles.（2）In this work,2D siloxene sheets were firstly fabricated via topotactic transformation of layered calcium silicide（CaSi₂）.Subsequently,the Ir NPs/Siloxene catalyst was prepared via the in situ hydrothermal reduction of Ir Cl ₆^2-by Si–H groups on siloxene.The morphology and microstructure of the catalysts were analyzed by SEM,TEM,XRD,XPS,FT-IR and Raman spectrometers.The content of the noble metal in catalyst was measured by ICP-OES.LSV,CV,electrochemical impedance spectroscopy（EIS）and chronoamperometry（I-t）measurements were used to explore the electrocatalytic hydrogen evolution reaction performance of Ir NPS/Siloxene.The prepared Ir NPS/Siloxene catalyst（2.1 wt%Ir）shows remarkably excellent electrocatalytic activity in 0.5 M H₂SO₄ medium,η₁₀ is 31 m V,Tafel slope is 29.4m V×dec^-1.In addition,Ir NPS/Siloxene catalyst also show s good mass specific activity and long-term stability in acidic solution.（3）The siloxene-reduced graphene oxide composite aerogel loaded with Ir nanoparticles（Ir NPs/SGH）were prepared by hydrothermal method using iridium chloride,siloxene and graphene oxide as precursors.The morphology and microstructure of the prepared materials were characterized by SEM,TEM,XPS,FT-IR and XRD.The content of the noble metal in catalyst was measured by ICP-OES.LSV,CV,electrochemical impedance spectroscopy（EIS）and chronoamperometry（I-t）measurements were used to explore the electrocatalytic hydrogen evolution reaction performance of Ir NPs/SGH.The results show that the Ir content of Ir NPS/SGH is2.3 wt%.In 0.5 M H₂SO₄ medium,Ir NPs/SGH catalyst shows remarkably excellent mass specific activity and electrocatalytic stability,η₁₀ is 32 m V and Tafel slope is23.8 m V×dec^-1.