Study On The Stability Of Pt/TiB₂ Catalyst For PEMFC

The stability of catalyst seriously restricts the commercialization of PEMFC. Pt/C and PtM/C are the commonly used in PEM fuel cell.However,due to the weak cohesion between Pt and carbon support,the Pt nanoparticles will readily move and agglomerate together.In addition,the carbon support can be corroded during the operation of PEM fuel cells which seriously influences the stability of catalysts. Thus,to prevent the corrosion of supports,here,TiB₂ as a conductive ceramic with high corrosion resistance is considered as catalyst support in this thesis. Simultaneously,to solve the issue of inertness of ceramic surfaces,we introduce functional macromolecules such as Nafion and polyaniline to modify the surface of Pt nanoparticles or TiB₂ conductive ceramic support to increase the interaction between Pt and TiB₂ as well as improve the distribution of Pt nanoparticles on support.The Nafion and polyaniline modified Pt/TiB₂ catalysts were synthesized, and then their physical properties,thermal and electrochemical stabilities were characterized.First,the TiB₂ conductive ceramic was synthesized by Self-propagation High Temperature Synthesis method(SHS)with the average diameter of 2～3μm.The thermal and electrochemical stability of TiB₂ is superior to that of traditional carbon support(Vulcan^?XC-72).Both the colloid and the liquid reduction routes were employed to prepare the Pt/TiB₂ catalysts modified with Nafion,and denoted as Nafion-Pt/TiB₂ and Pt/Nafion-TiB₂ catalyst,respectively.The electrochemical surface area of Nafion-Pt/TiB₂ and Pt/Nafion-TiB₂ obtained by CV decreased to 40%after 6000 and 7500 potential cycles,respectively,showing 2.5 to 3 times longer than that of commercially available Pt/C catalysts.Meanwhile,the mass loss rate of Nafion-Pt/TiB₂ and Pt/Nafion-TiB₂ catalysts before 500℃C is 2.18%and 2.03% respectively by TG-DTA analyses,whereas the Pt/C loss is 80.41%,which shows the Nafion modified Pt/TiB₂ is more thermally stabile than that of Pt/C. The polyaniline(PANI)modified Pt/TiB₂ catalysts were synthesized by chemical oxidation process.The electrochemical surface area of PANI modified Pt/TiB₂ still preserves 50%even after 6300 CV cycles,whereas the commercial Pt/C decreases to 49.82%after 1200 CV cycles.It shows 5 times longer electrochemical stability than that of Pt/C.Meanwhile,there is no mass loss observed before 500℃, while the loss of Pt/C is 56.29%at 455℃.Consequently,the Pt/TiB₂ catalysts modified by Nafion or PANI have remarkable high stabilities compared with that of commercially available Pt/C.It is noted that the TiB₂ modified by PANI have much higher stability than that modified by Nafion.The mechanism of the stability of functional polymer modified Pt/TiB₂ was discussed.The remarkable high electrochemical stability of TiB₂ supports and the adhesive effect and steric effect of functional polymers such as Nafion and PANI were regarded as the key factors.