Investigation On Oxygen And Nitrogen Electroreduction Properties Of Gold Based Catalysts

With the increasing problems about energy in the world today,the traditional high-energy industry model based on fossil energy is unsustainable,and the road to green development of sustainable energy is imminent.Proton exchange membrane fuel cells（PEMFCs）have the advantages of high efficiency and stability,continuous operation,easy storage and carrying,high theoretical specific energy,and near zero pollution discharge.However,the slow cathode dynamics of fuel cells has always hindered its development in practical applications.It is crucial to improve the activity of the cathode oxygen reduction reaction（ORR）catalyst in order to improve the performance of fuel cells.On the other hand,ammonia（NH₃）is one of the most important inorganic compounds which can be widely used as a main raw material for nitrogen fertilizers,industrial chemicals and clean energy carrier.Until now,NH₃ is mainly synthesized by combining hydrogen（H₂）and nitrogen（N₂）under high temperature and pressure,which requires high energy supply consumption.Electrochemical nitrogen reduction reaction（NRR）is an effective alternative to the synthesis of NH₃.In this thesis,we designed nanoporous metal catalysts and silver-gold alloy nanotube catalysts for cathodic oxygen reduction and electrochemical nitrogen reduction.The specific research includes the following two aspects:（1）Pt with high coordination number（HCN）located in the defect surface sites is favorable for high oxygen reduction reaction activity.Here,using nanoporous Au（NPG）that intrinsically possesses a higher proportion of HCN Au atoms over traditional nanoparticles,we epitaxially deposit Pt monolayer onto NPG to inherit the high-density HCN Pt sites.It is proved that the one with a smaller ligament size possesses a higher proportion of HCN Pt atoms as for the NPG-Pt catalysts.Thus,exhibiting a 5.2-fold specific activity and 18.7-fold mass activity enhancement than the commercial Pt/C catalyst.Moreover,depositing Au atoms on the NPG-Pt surface can increase the HCN Pt surface exposure further leading to a 6.9-fold specific activity and 19.1-fold mass activity increase as compared to Pt/C.（2）The composition-activity relationship of Ag Au alloy nanotube is systematically investigated.It is found that the atomic ratio of Ag Au nanotubes rises from 8:1 to 1:2,Ag₂Au₁ alloy nanotubes achieve the largest enhancement for NRR catalytic activity.The NH₃ production rate and faradaic efficiency of Ag₂Au₁nanotubes are 21.7μg h^-1 mg^-1_cat and 3.8%at-0.30 V vs.RHE,respectively,which were 3.0 and 3.6 times higher than those of Ag nanowires.Moreover,Ag₂Au₁ hollow nanotubes still demonstrate a superior NRR catalytic activity compared to Ag₂Pd₁ and Ag₂Pt₁ nanotubes.