Preparation And Properties Of Platinum-based Bimetallic And Platinum Nanowire Catalysts For Oxygen Reduction

With the progress of human science and technology,energy conservation and environmental protection have become the core of sustainable development strategy of human society,influencing the energy decision making and technology orientation of all countries in the world.Meanwhile,It is also a tremendous driving force for the development of energy technology.In all kinds of new energy technology,Fuel cell is a kind of power generation device that directly converts chemical energy stored in fuel and oxidant into electric energy.Among them,proton exchange membrane fuel cell is an efficient,clean and new energy source.Energy conversion efficiency of proton exchange membrane fuel cell is not limited by Carnot cycle,Conversion efficiency can generally reach about 60%.Water is the only discharged product and the products do not pollute the environment.Proton exchange membrane fuel cell(PEMFC)has its unique characteristics,It has been more and more widely used in many fields such as transportation,military affairs,communications and so on.In the past ten years,Countless top scientists have worked hard for it,Some technical difficulties need to be overcome in the real large-scale commercial application of proton exchange membrane fuel cells.The main thing is the cost of the catalyst,With current technology,Platinum metal is the basis of large scale production of fuel cells.Global platinum resources are not only limited in reserves,but also expensive in price,This leads to high fuel cell costs.At cathode of proton exchange membrane fuel cell,Oxygen reduction kinetics is slow,which results in a much higher platinum load on the cathode of fuel cell than on the anode,Therefore,it is necessary to develop a high performance cathode catalyst.At present,commercial platinum-carbon catalysts are widely used,but commercial platinum-carbon catalysts still have some inherent shortcomings.In order to improve the activity and stability of cathode catalyst for fuel cell,In this paper,nanoporous gold-based catalysts and platinum nanowires were used as oxygen reduction catalysts,respectively,The relationship between their morphology and properties was discussed,and their performances in electrocatalysis and fuel cell were also discussed,Specific discussions are as follows:(1)Nanoporous metals prepared by dealloying have attracted more and more attention due to their special structure.Nanoporous gold can be prepared by etching commercial Au-Ag alloy films in appropriate solutions.The oxygen reduction performance of nanoporous gold epitaxially supported single-layer platinum shell,double-layer platinum shell,platinum nanoparticles and platinum-carbon catalyst was systematically studied.The results show that the oxygen reduction reaction on nanoporous gold-based catalysts is carried out through four-electron pathway.In addition,the double-layer platinum shell supported by nanoporous gold epitaxy shows good stability.(2)Compared with zero-dimensional cathode catalyst,Platinum nanowires as one dimensional cathode catalyst exhibit single crystal anisotropy,It has higher aspect ratio,fewer lattice boundaries,longer smooth crystal surfaces and fewer surface defect sites.These are ideal properties of fuel cell oxygen reduction catalysts.One dimensional structure preferentially exposes low energy crystal surfaces with high oxygen reduction activity,Surface oxidation can be delayed at high potential,Thus the kinetics of oxygen reduction is enhanced.The path-directing effect of structural anisotropy can improve the transmission characteristics of electrons.Using platinum nanowires as cathode catalyst,the effects of various factors on the discharge performance of fuel cells were preliminarily discussed from three aspects: platinum loading,carbon loading of catalytic layer and resin loading of catalytic layer.The results show that platinum loading requires two factors: slow equilibrium oxygen reduction kinetics and nanowire aggregation,Carbon loading in catalytic layer requires two factors: equilibrium material transfer distance and platinum nanowire agglomeration,The resin content in catalytic layer needs to avoid flooding of catalyst.