The Study Of Platinum And Platinum-cobalt Electrocatalyst Prepared By Magnetron Sputtering

Recently,Pt/C catalyst is still the most common catalyst which is used in the proton exchange membrane fuel cell,but as a result of limited and expensived Pt resource,the fuel cell commercialization process is restricted.In order to reduce the cost of the fuel cell and promote its commercialization process,we must improve the catalyst preparation methods or change the structure of the catalyst to advance the utilization of Pt and reduce the loading of Pt catalyst.At present,the methods of making the Pt/C catalyst are mainly impregnation method,colloid method and micro-emulsion method,etc.,but these methods need to be operated verbosely.Scattering catalyst in the gas diffusion layer or the proton exchange membrane also easily lead to heterogeneous dispersion,besides,just using Pt as catalyst resulting a problem that Pt has low activity and is easily to be poisoned.Magnetron sputtering method is a physical method which is operated relatively simply.In the low-pressure argon atmosphere,magnetic field and electric field interact,argon ion impacts the target material,making the sputtering particles homogeneously dispersed on the substrate,and improving the uniformity of the catalyst,indirectly reducing the thickness of the catalytic layer.In this paper,the method of magnetron sputtering was used.First of all,we made the reduced graphene oxide layer on carbon paper as a base,depositing Pt on the surface with direct current sputtering.Because of the high density of reduced graphene oxide,Pt could not fall inside the carbon paper,which improves the utilization of the Pt.Secondly,we made the gas diffusion layer as a base,direct current sputtering Pt and double target sputtering Pt and Co on the surface,using the motivation of the activity of Pt by Co to reduce the loading of Pt.The specific research work are as follows:Firstly,we coated graphite oxide solution onto the carbon paper,after the thermal reduction in Ar-H2 gas mixture,Pt was deposited on the surface of the sample with dc sputtering,then a gas diffusion electrode with optimized structure had been prepared.We have examined the concentration of graphite oxide solution and the reduction temperature which can influence the coverage and the reductivity of the reduced graphene oxide,and studied the gas flow and the thickness of Pt during the sputtering which can influence the morphology and performance of the gas diffusion electrode.The results showed that the 1 mg·ml-1 graphite oxide solution has the best coverage,and the higher the reduction temperature is,the less the O content in the reduced graphene oxide is,the higher reductivity the reduced graphene oxide has.With the increase of the sputtering thickness,the suface of Pt thin film appear obvious bulge and gully morphology.Pt membrane which sputtered with 30 sccm gas flow rate and thickness of 10 nm has the best power density of 175.6 mW·cm-2,and the highest electrochemical surface area of 65.4 m2·g-1.From the above results,we have found that reduced graphene oxide can effectively prevent the Pt from falling into the carbon paper.The convex shape on the surface of Pt thin film could improve the active area of Pt.Proper thickness and gas flow can make it achieve the optimal effect and make the catalyst exert the best catalytic activity.In order to decrease the loading of Pt in the catalyst.Firstly,we deposite Pt onto the gas diffusion layer with direct curent sputtering.We change the thickness of Pt and test it as the cathode gas diffusion electrode of proton exchange membrane fuel cell.The results show that without using carbon carrier,the cell performance is still well.When the sputtering thickness is 80 nm and the loading of Pt is 0.20 mg·cm-2,the fuel cell has the maximum power density of 691.7 mW·cm-2.Then,we adopted the method of double target sputtering,Pt with direct current sputtering and Co with radio frequency sputtering,deposited Pt and Co on the diffusion layer at the same time.After heat treatment in hydrogen and argon atmosphere,the single fuel cell performance has been tested.Results show that as the same thickness of the catalytic layer,the difference of the fuel cell performance of the two kinds of catalyst is not obvious.From the above results,we have found that high temperature treatment make the Co and Pt form alloy structure,the addition of Co improves the catalytic activity of Pt,maintains the performance when the loading of Pt have significant declined.