The Design On Low Content Of Noble-metal Nanomaterials And Study On Electrocatalytic Performance

With the continuous development of society and the increase of population,the global energy demand is also growing rapidly.The current over-dependence on fossil fuels has led to rapid energy consumption as well as environmental pollution and global warming.With the increasingly severe energy crisis and environmental problems,the development of clean energy system aiming at low carbon or no carbon energy has become the focus of attention.In this case,electrocatalysis technology emerged.Hydrogen evolution reaction（HER）,as one of the half reactions of electrocatalytic water decomposition to produce hydrogen,has attracted wide attention in the past few decades,but it has not been widely used at present due to the cost and activity of catalysts.In addition,the relatively mature methods used to produce nitrate need to be carried out in the environment of high temperature and pressure,which will produce high energy consumption and pollution to the environment.Therefore,it is particularly important to study the technology of electrocatalytic nitrogen oxidation（NOR）to produce nitric acid.Compared with the performance of non-noble metal catalysts,noble metal materials still have irreplaceable advantages in electrocatalysis.Since precious metal content is relatively low and expensive,different strategies have been designed to reduce the amount of precious metal and increase the intrinsic activity of catalysts.On this basis,the design of low noble metal content nanomaterials and their applications in electrocatalytic hydrogen evolution and nitrogen oxidation are discussed.The main research contents are as follows:（1）In the first chapter,we consider doping a small amount of precious metal M（M=Pt,Ru,Pd）were used as H*adsorption and H₂ desorption sites,using carbon nanotubes（CNT）as substrate prepared Pt-Ni₄Mo nanoparticles with small size（3-4 nm）.Thanks to the electronic control between precious metals and alloys,the material showed amazing reactivity and stability during the electrocatalysis of HER.The electrochemistry test in 1.0 M KOH solution showed that the overpotential of Pt-Ni₄Mo@CNT at 10 m A cm^-2 was only 18.6 m V.In addition,the catalyst showed a large turnover frequency（TOF）value at 100 m V and no significant change in catalytic activity after 200 h at 100 m A cm^-2,indicating that the catalyst has high intrinsic activity and excellent durability.According to in-situ characterization and theoretical calculation results,Ni₄Mo mainly plays the role of water dissociation during HER,promoting the formation of H*and OH*,and then the strongly adsorbed H*is transferred to the Pt site,which not only exposes the active center of Ni₄Mo component to continue to participate in the reaction,but also accelerates the desorption process of H₂.This original strategy will provide valuable inspiration for the design and synthesis of other catalysts in the future.（2）In the second chapter we doped a small amount of precious metal M（M=Ir,Ru,Pd） in order to optimize the adsorption-desorption energy of the material,designed and synthesized the Ni/Ni O heterojunction nanoparticles loaded on carbon nanotubes.The electrochemical test showed that Ir-Ni/Ni O@CNT had superior performance in 1.0 M KOH,and the overpotential was as low as 24.6 m V at 10 m A cm^-2.In addition,the TOF value of the catalyst can reach 2.51 s^-1 and the exchange current density can reach 4.34 m A cm^-2,indicating that the catalyst has good intrinsic catalytic activity.Density functional theory（DFT）further proves that Ni O surface is favorable to the adsorption of OH*in Volmer step,while Ni tends to adsorb H*,which jointly promotes the water decomposition reaction.Meanwhile,the synergistic effect between noble metal Ir and non-noble metal Ni/Ni O improves the catalytic rate of HER.This work will provide valuable contribution and enlightenment for large-scale production of high-performance nickel-based electrocatalysts.（3）In the third chapter,we regulating the electronic structure between precious metals and non-precious metals through heterogeneous engineering,designed and synthesized a small size（4 nm）Pd-Mn₃O₄/CNT heterojunction nanocatalyst.After a series of electrochemical tests,the nitrate yield of Pd-Mn₃O₄/CNT catalyst in O₃-saturated 0.1M Na₂SO₄ electrolyte is 85.3 mg h^-1mg_cat^-1,far exceeding all the nitrogen oxidation electrocatalysts previously reported.The Faraday efficiency reached 85.8%at 1.6 V vs.RHE.In addition,the calculation after the test found that NO₃^-production rate reached the milligram-per-hour level,which is expected to be used for large-scale nitrate production.DFT calculations show that the heterogeneous structure modulates the electronic structure of Pd and Mn₃O₄ components into two different active sites,resulting in strong adsorption effects on N₂ and O₃.This accelerates the conversion of nitrate based on the direct formation mechanism and reduces the energy barrier,thereby increasing the reaction rate and nitrate yield of electrocatalytic nitrogen oxidation.