Study On Hydrophilicity And Hydrophobicity Of Platinum Based Catalysts By Magnetron Sputtering And Structural Hydrophobic GDL

Proton Exchange Membrane Fuel Cell has attracted significant attention as green and efficient energy devices due to its high efficiency,high performance and environment-friendliness,which can be broadly applicated in transportation,power station and portable power source.However,excessive water produced during operation in PEMFC will cause flooding,which cover the active site of the catalyst Pt,hinder the diffusion of oxygen and result in the voltage instabilities and battery performance degration.Therefore,effective water management is a key factor in determining fuel cell performance and durability.At present,the water management of fuel cell faces two important issues:First,the magnetron sputtering Pt electrode is too hydrophilic to be practically applied while the preparation of low Pt electrode.The hydrophilic problem of Pt electrodes need to be solved.Second,in order to remove a large amount of water generated during the high current operation,it is necessary to further increase the hydrophobicity of the gas diffusion layer.In order to improve the water management capacity and solve the problem of flooding,this paper mainly have done the following two aspects of work:the first was to change the hydrophilicity and hydrophobicity of Pt through alloying.The Ag element with low surface energy was alloyed with Pt through theoretical calculation,and the Pt-Ag alloy catalyst was formed by magnetron sputtering technology.The contact angle test of the hydrophilicity and hydrophobicity of the Pt-Ag alloy catalyst was carried out.Phase,morphology and electrochemical catalytic activity were detected.The second was to prepare hydrophobic GDL by template imprinting.Through template imprinting technology,the microporous layer was scraped and imprinted on the surface of carbon paper to prepare the GDL with channel structure and surface hydrophobicity.Moreover,the effect of channel size on the hydrophobicity,permeability and porosity of GDL was studied.Finally,in order to study the effect of the channel structure GDL on the performance of PEMFC,the channel structure GDL was applied to the cathode side of the single cell.The main conclusions drawn in this paper are as follows:（1）The surface contact angle value of Pt and Ag metals by magnetron sputtering were less than the theoretically calculated value of Pt and Ag metals,but the trend remained unchanged,and the surface contact angle value of Ag was still greater than that of Pt.Most Pt-Ag alloys followed the law of composite materials,and the surface contact angle increased with the addition of Ag metal in the alloy.However,since the contact angle of Ag by magnetron sputtering was only 49.5°,the surface of Pt-Ag alloy by magnetron sputtering did not reach hydrophobic state.In addition,a unique phenomenon was found.When the Pt₄Ag alloy was formed,the surface contact angle value was 16.0°,which was smaller than that of the metal Pt（30.0°）.（2）The electrochemical active area of the sputtered Pt₄Ag and Pt₂Ag₃ thin-film electrodes were 35.5 m²/g and 68.2 m²/g,respectively,which were larger than the ECSA of the pure Pt thin-film electrodes（27.4 m²/g）,and the ECSA of Pt₂Ag₃ alloy thin-film electrode was 2.5 times that of sputtered Pt thin-film electrode;area specific activity of the Pt,Pt₄Ag,Pt₂Ag₃ thin-film electrode were 717.4μA/cm²,637.6μA/cm²and 852.7μA/cm²,respectively.The SA of the Pt₂Ag₃ alloy thin-film electrode was135.3μA/cm² higher than that of the sputtered Pt thin-film electrode.It showed that Pt-Ag alloy catalyst had better electrocatalytic performance than the pure Pt.（3）The surface contact angle of the GDL with groove structure was larger than that of the plane GDL,and with the channel width increasingly narrower,the surface roughness and the surface contact angle both increased.When the channel width was75μm,the GDL surface contact angle reached 148.5°,which showed high hydrophobic surface characteristics.（4）The three GDLs with diffirent channel structures had similar gas permeability.Compared with flat GDL,the gas permeability of the GDLs with diffirent channel structures expanded by 50%.（5）Under the high current density,the battery performance of the channel structure GDL was better than the flat GDL,especially when the channel width was 75μm,the battery reach peak performance.under 100%RH and the current density of3000 m A/cm²,the maximum power that the GDL with a channel width of 75μm battery could achieve was 11.1%higher than that of the flat GDL;as for GDL with 75μm channel width,with the humidity decreasing,the advantage of battery performance was more obvious at high current density;the maximum power of the GDL was 18.1%,higher than that of the flat GDL at 0.5 V with 25%RH.The narrower the channel width,the better the battery performance.