Composition Optimization And Design Of Titanium Alloy Bipolar Plate For Proton Exchange Membrane Fuel Cell

With the development of the economy and society,energy issues are drawing increasing attention throughout the world.The over-exploitation and utilization of conventional fossil resources,such as oil and coal,have led to the depletion of energy and the deterioration of environment.Thereof,it is a hot spot to explore non-polluting and renewable new energy sources.Fuel cell,a kind of efficient and environmentally friendly power generation system which can continuously convert chemical energy into electricity directly,is the fourth power generation of device since hydropower,thermal power and nuclear power.Among them,proton exchange membrane fuel cells show prominent advantages of long life,high specific power and specific energy,fast start-up at room temperature,etc.,and have been widely applied in military,transportation and portable energy fields,which are considered as one kind of the ideal power sources to meet the requirements of future energy and environment.The bipolar plate,which is one of the core components of a proton exchange membrane fuel cells,occupies a large part of the quality and cost of the whole battery pack and has the functions of uniformly distributing the reactant gas,conduction current,and series connection battery,etc.In order to satisfy these functions,the ideal bipolar plate should have characteristics of high thermal conductivity,electrical resistance,corrosion resistance,low density,good mechanical properties,low cost,easy processing and so on.However,the bipolar plates currently produced have problems of poor corrosion resistance,poor conductivity matching,high production cost and short service life.Accordingly,it is crucial for commercial applications of fuel cells to achieve a reasonable matching of the conductivity and corrosion resistance of the bipolar plate materials,in other words,to ensure high corrosion and service life of the entire system resistance in the case of reasonable conductivity.Conventional bipolar plate materials,such as metals,graphite and composite materials,can not be used directly as bipolar plate due to a poor combination of high strength,conductivity,corrosion resistance,gas resistance and low cost in the environment of proton exchange membrane fuel cell.Therein,pure Ti possess an excellent comprehensive properties,however,it is easy to form TiO₂ layer with a poor conductivity on its surface,which hinders its commercial application.It has been reported that the conductivity of passive film can be improved by adding a certain amount of Nb/Ta elements into pure Ti,but the corrosion resistance of passive film can also be affected.In this paper,a series of binary and ternary Nb/Ta added to Ti-based alloys with the guide of the cluster formula approach were prepared by suction-cast processing.And the variation of properties of Ti-based alloys with added Nb/Ta elements was investigated.The conclusions are as follows:In binary Ti alloys,the corrosion resistance of manor-alloying Ti alloys is mainly affected by alloying elements and microstructure.When the alloy is single phase structure,the corrosion resistance of the alloy is closely related to the alloying elements,i.e.,with the increasing of Nb/Ta alloying elements,the corrosion resistance of the alloy in battery environment is improved.However,when the alloy are composed of multi-phase,its corrosion resistance is affected by both alloying elements and microstructure.It is well-known to us all that the alloying elements can improve the corrosion resistance of pure Ti to a certain extent.However,under service conditions,due to the influence of battery environment and loading voltage and current on the alloy,micro-batteries tend to be formed between multi-phases,which seriously affects the corrosion resistance of the alloy and reduces the corrosion resistance of the material.The thickness of pure Ti passivation film increases with time.However,when the Nb/Ta alloying element is added to pure Ti,the thickness of passivation film decreases significantly,which indicates that the addition of Nb/Ta alloying element can effectively inhibit the increment of thickness of passivation film.In addition,the contact resistance of Nb/Ta manor-alloying Ti alloys decreases with the increase of Nb/Ta content.In contrast,the ternary alloys with the same amount of alloying elements exhibit similar variation tendency,but the comprehensive properties of ternary alloys are worse than that of binary alloys.Moreover,The addition of Nb and Ta shows similar variation tendency to the properties of the alloy,but in contrast,the addition of Ta makes the Ti alloy show better comprehensive properties.It was found that the solubility of Ta element in alpha-Ti is limited,and the precipitated second phase has a great influence on the corrosion resistance of the alloy.Therefore,in order to ensure the corrosion resistance of the alloy,the addition of alloying element Ta should not exceed 3.125 at.%.