Preparation Of Graphene Supported Palladium-copper Composites And Investigation Of Its Electrocatalytic Performance

Proton exchange membrane fuel cells（PEMFC）have received widespread attention in recent years due to their advantages of low environmental pollution,high energy density,high conversion efficiency,and easy operation and use.However,the performance of PEMFC mainly depends on its anode and cathode catalysts.At present,Pt catalysts is the most widely used catalysts.However,the precious metal Pt not only has limited resources,but also causes catalyst poisoning,which largely limits the commercial application of PEMFC.Metal Pd has become a research object of many scholars in recent years due to the relatively low cost and the anti-poisoning ability.However,at present,due to the nano-size effect,it is still a great challenge to prepare Pd nanoparticles with high dispersion and small size.The formation of PdCu alloy catalyst material between Pd and the second phase transition metal Cu can help solve the problem of agglomeration of nanoparticles and improve the activity and stability of the catalyst through the strain effect and ligand effect.Graphene has a huge theoretical specific surface area and excellent electrical conductivity,and nitrogen-doped graphene obtained from polyaniline as a nitrogen source contains rich defect sites.Both are used as carriers for metal catalysts,which are beneficial to the anchoring and dispersion of metal nanoparticles.Therefore,in this paper,graphene and nitrogen-doped graphene are used as carriers to support PdCu alloy catalysts,and their effects on the anodic formic acid oxidation（FAO）and the cathodic oxygen reduction reaction（ORR）are discussed respectively.The main research contents are as follows:（1）Composite catalysts（Pd-Cu/rGO）are successfully prepared via a facile hydrothermal approach.XRD,TEM,SEM,XPS and AAS were used to characterize the phase structure,micro-morphology,surface state and composition of the matrial.The electrocatalytic performance of the catalyst for FAO was tested by CV（cyclic voltammetry）and CA（chronoamperometry）.The results show that the addition of Cu can greatly improve the electrocatalytic performance of the catalyst in FAO process.With the optimized condition of Pd/Cu 3/1,p H 10,t emperature 120℃and the amount of hydrazine hydrate 2 m L,our Pd₃Cu₁/rGO catalyst has the smallest size（～2.12 nm）and largest electrochemically active area(57.82 m² g_Pd^-1)with Pd-Cu alloy nanoparticles uniformly distributed on graphene sheets,and demon strates an excellent catalytic activity with current density of 1580 m A mg_Pd^-1 and residual current of 69.93m A mg_Pd^-1 at 3000 s.In addition,it is worth to note that the load amount for palladium is only 14.5%.（2）Graphene oxide and aniline monomers are used as raw materials to form GO-PANI with different mass ratios through heterophasic nucleation of polyaniline.On one hand,Pd₃Cu₁ was directly supported on the composite carrier（GO-PANI）to obtain Pd₃Cu₁/rGO-PANI composite catalyst material;on the oth er hand,GO-PANI is first heat-treated to obtain N-rGO,and then Pd₃Cu₁ is loaded on N-rGO to obtain Pd₃Cu₁/N-rGO composite catalyst material.XRD,SEM,TEM,FT-IR,RAMAN and XPS were used to characterize the structure,morphology,chemical composition,an d surface state of the material.The electrocatalytic activity and stability of the catalyst for ORR were tested by LSV（Linear Scanning Voltammetry）and CA,and compared with commercial Pt/C（20 wt.%Pt）.The results show that Pd ₃Cu₁/rGO-1PANI（10wt.%Pd）composite catalyst material has small alloy nanoparticle sizes（～5 nm）,good dispersion,and excellent catalytic activity for ORR.However,compared with commercial Pt/C（20 wt.%Pt）catalyst,it still has a certain gap on the electrocatalytic performance for ORR.GO-PANI with different mass ratio was first heat-treated at700℃for 2 h to obtain N-rGO,and then Pd₃Cu₁ alloy was loaded on N-rGO.The resulting Pd₃Cu₁/10N-rGO（10 wt.%Pd）composite catalyst material has～2.47 nm alloy nanoparticles.In addition,the catalytic performance for ORR is close to commercial Pt/C（20 wt.%Pt）catalyst.Finally,we research that the GO-PANI（1:10）composite carrier is first heat-treated at different temperatures to obtain 10N-rGO-T（T=700℃,800℃,900℃）,and then Pd₃Cu₁ alloy was loaded on 10N-rGO-T.The obtained Pd₃Cu₁/10N-rGO-800 composite catalyst material has the smallest nanoparticle size（～1.75 nm）,and contains a large amount of pyridinic nitrogen,graphitic nitrogen and defect sites.The actual content of Pd in the catalyst is only 8.5wt.%.The catalyst shows better catalytic activity and stability for ORR than the commercial Pt/C（20 wt.%Pt）catalyst.