Synthesis And Electrocatalvtic Performance Of Graphene Aerogel Decorated With AuAg@Pt(Pd) Nanowires

With the increasing demand for traditional energy,the development of green,efficient and sustainable new energy has become an important measure to solve the energy crisis,Fuel cells as a new type of energy device,have the advantages of high energy density,environmentally friendly,no noise and long service life,therefore have achieved promising prospects in the field of electric vehicles and other commercial field,Water splitting is an important technique to produce hydrogen nowadays.The cathodic reaction of fuel cells-oxygen reduction reaction(ORR)which play as an important role in determining the performance of fuel cells,besides,the cathodic reaction of water splitting-hydrogen evolution reaction is a core step to produce purity H2,thus,it is crucial to design efficient,low-cast ORR and HER bifunctional electrocatalysts for sustainable development of new energy system.Pt-based metal and its alloy exhibit superior ORR and HER activity,however,its high-cost and scarcity has limited the commercial application.Pt-based alloy nanowires can improve the efficiency of Pt,reduce the cost,besides,the synergistic effect between Pt and other metals further can improve the catalytic activity.However,the stability of pure nanowires is not good enough to satisfy its application as electrocatalysts,in order to solve this problem,thus graphene aerogel decorated with Pt-based alloy nanowires is a good strategy to reduce cost,enhance the catalytic activity and stability of ORR and HER,which considering that graphene have the advantages of high specific surface area,good electrical conductivity and extensive sources.Based on this,this research focuses on preparation of the graphene aerogel decorated with AuAg@Pt nano wires and AuAg@Pd nano wires,respectively.Furthermore,this thesis gives more analysis of ORR and HER activities and reaction mechanism.The mainly research work are shown as below:(1)This thesis prepared the graphene aerogel decorated with AuAg@PtNWs(AuAg@PtNWs/GA)and graphene aerogel decorated with AuAg@PdNWs(AuAg@PdNWs/GA)by ultrasonic emulsification method and hydrothermal reduction method,respectively.then,compared the morphology,structure and the elasticity of the samples prepared by the above two methods.The AuAg@PtNWs/GA contains smaller size of AuAg@PtNWs insides,and its loading is low,the length of AuAg@PtNWs is about 100-200 nm,compared with the pure AuAg@PtNWs,it is obviously that there exists much fracture in nanowires,therefore,the stability of the AuAg@PtNWs/GA prepared by ultrasonic emulsification is not stable.However,the AuAg@PtNWs/GA prepared by hydrothermal reduction method which shows better stability with the size of 300-500 nm,respectively.The results of Ramanspectra and FTIR exhibits that there are lots of oxygen-containing functional groups such as hydroxyl,carboxyl group and carbonyl group existed in the AuAg@PtNWs/GA.(2)Then the ORR activity and mechanism of AuAg@Pt(Pd)NWs/GA were studied in 0.1 M KOH solution,the initial reduction potential of AuAg@PtNWs/GA,AuAg@PdNWs/GA and 20%Pt/C were 0.92,0.86 and 0.94 V,respectively.what's more,the corresponding peak current density were 4.85,2.16 and 5.58 mA/cm2.These results shown that the graphene aerogel decorated with nanowires can improve the electron and mass transfer,thus enhance the ORR activity.Besides,by the rotating disk tests,the number of electron transfer of AuAg@PtNWs/GA,AuAg@PdNWs/GA and Pt/C in ORR were calculated to be 3.94,2.37 and 3.92,respectively.it is indicated that AuAg@PtNWs/GA conform the 4 electrons reaction process,which transform into H2O directly.(3)Then the HER activity and mechanism of AuAg@Pt(Pd)NWs/GA were studied in 0.5 M H2SO4 solution,the overpotential of AuAg@PtNWs/GA,AuAg@PdNWs/GA and 20%Pt/C were 69,82 and 25 mV at 1 mA/cm2,the slope of Tafel were 58,74 and 28 mV/dec,respectively.the catalytic activity of AuAg@PtNWs/GA was similar to that of 20%Pt/C catalyst.The HER reaction of AuAg@PtNWs/GA was consistent with volmer-heyrovsky mechanism.To sum up,we utilized the three-dimensional network structure of graphene and synergistic effect of Pt-based alloy nanowires,focused on the cathodic reaction of fuel cells and water splitting(ORR and HER),We designed a bifunctional electrocatalyst towards ORR and HER which can low the cost,improve the catalytic activity and stability.Although,AuAg@PtNWs/GA shown slightly inferior to 20w%Pt/C,however,considering of the Pt loading of AuAg@PtNWs/GA is only about 9wt%theoretically,it still has the cast advantage.The method is facile in operation and the carbon materials are widely available,so it provides a possibility for the large-scale preparation of bifunctional electrocatalyst.