Study On Preparation And Properties Of Graphene-based Low-platinum Catalysts For Low Temperature Fuel Cells

At present,the reduction of traditional energy and the harm to the environment in utilization cause people's deep reflectionand recyclable clean energy has attracted more and more attention.A fuel cell is a power generation device that directly converts chemical energy which stored in the fuel into electricity with high efficiency and its use can effectively solve the problem of environmental pollution and energy crisis.Among them,low-temperature fuel cell has the characteristics of high energy conversion efficiency,low working temperature,high safety and friendly environment,and has great developing potential in mobile power,power battery and daily life power.Catalyst is very important to fuel cells,and it is found that Pt is most suitable as a active component for low-temperature fuel cell catalyst because of its special electronic structure,but Pt has the following shortcomings: resource scarity of Pt in the world and high commercial price cause the high cost of the catalyst material;Pt is easily poisoned by the CO intermediate generated during alcohol oxidation process,which reduce the catalyst activity greatly.In addition,the catalyst support has important influence on the performance of the catalyst.Graphene has high electron transfer rate and large specific surface area because of its special monolayer carbon atom structure,and is suitable to be a catalyst carrier.However,the graphene sheets are easy to accumulate due to the van der Waals force,which reduce the catalyst performance.The above problems have seriously hindered the development and commercialization of low temperature fuel cells.In this paper,a series of Pt-based catalysts based on graphene were prepared and the catalytic performances of these catalysts in the anode of low temperature fuel cells were studied.Firstly,Pt/Gr-C catalyst was prepared by embedding Vulcan XC-72 carbon into the graphene layer to solve the problem of graphene restacking.It was found that the Pt particles with average particle size of about 2 nm were highly dispersed on the surface of graphene..The graphene layer was fluffier and the defects of graphene were more and more disordered after carbon doping.The specific surface area of the graphene was enhanced,and thus the catalyst activity was improved.The electrocatalytic activity of Pt/Gr-C for methanol oxidation was 0.3 A mg_Pt^-1,which was 1.4 times and 1.7 times larger than those of Pt/Gr(0.22 A mg_Pt^-1)and Pt/C(0.18 A mg_Pt^-1),respectively.Secondly,in order to improve the anti-toxic ability of Pt catalyst to CO,PtCo alloy catalyst?PtCo/RGO?was prepared by one step reduction method.It was found that the addition of Co changed the electronic structure of Pt and weakened the interaction between Pt and CO,and thus improving the anti-poisoning ability.PtCo nanoparticles have an average particle size of about 2.4 nm and are highly dispersed on the surfaces of graphene.The electrocatalytic activity of PtCo/RGO for methanol oxidation was 0.68 A mg_Pt^-1,which was 1.5 and 2.1 times higher than those of Pt/RGO and Pt/C catalysts,respectively.In addition,Pt/RGO had an If/Ib ratio of 1.3,which was 1.2 and 0.7 times higher than Pt/RGOand Pt/C,respectively,implying the high poisoning tolerance.Finally,in order to reduce the loading and increase the utilization of Pt,the graphene supported hollow PtCo nanospheres?H-PtCo/Gr?were prepared and their electrocatalytic oxidation performaces of methanol were studied.In the first step,Co nanoparticles with homogeneous size distribution were prepared by sodium borohydride reduction and the average particle size was about 20 nm In the second step,H-PtCo/Gr was prepared by chemical displacement between Pt2+ and Co.Finally,the graphite oxides were added and the H-PtCo/Gr was obtained.The activity of H-PtCo/Gr for methanol oxidation in sulfuric acid solution was 0.96 A mg_Pt^-1,which was 2.4 and 2 times higher than those of Pt/C and Pt/Gr,respectively,indicating that the high catalytic performance of H-PtCo/Gr.In addition,the ratio of forward peak current density?If?to reverse peak current density?Ib?of H-Pt Co/Gr for methanol oxidation in cyclic voltammogram is 1.28,which is much higher than Pt/C?0.82?and Pt/Gr?1.04?.