Preparation And Catalytic Properties Of Pt Alloy Catalysts Used For Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cells (PEMFCs) are considered as a promising clean power source for transportation, mobile and stationary applications and have been attracting much attention in recent years due to their high power density, high energy conversion, high efficiency, and clean utilization. Catalyst is one of the critical components determining the performance and cost and thus the final commercialization of PEMFCs. Up to now, the most practical electrocatalysts are still Pt based in the form of nanoparticles dispersed on carbon black supports due to their not yet surpassed high catalytic activity. In addition to the high cost of the scarce precious metal, current Pt catalysts also suffer from performance degradation during practical operation due to the high voltage, acidic and oxidation environment in PEMFCs. To improve the electrochemical activity and durability of conventional catalyst used in PEMFCs, this study focuses on Pt alloying and modification of carbon support.Firstly, Pt-Pd and Pt-Ir alloy catalysts supported on homemade carbon canocages (CNCs) are prepared by a liquid phase reduction method followed by heat treatment at different temperatures. XRD, TEM, ICP and XPS are used to characterize the morphology and structure of these catalysts, and CV and LSV are applied to evaluate the electrochemical activity and durability. Results show that the Pt-Ir alloy catalyst with Pt/Ir atomic ratio of1:1after heat treatment at400℃has a better activity and stability than Pt-Pd alloy catalyst.Secondly, two home made carbon nanocages (CNCs) with different degrees of graphitization are used to support the pure Pt and Pt-Ir alloy catalysts and their electroactive performance and durability are evaluated by accelerated durability tests (ADT). Results demonstrated that the Pt-Ir alloy catalyst supported on CNCs with a high degree of graphitization possesses a better performance and stability than the pure Pt catalyst.In conclusion, the Pt-Ir alloy catalyst with an atomic Pt/Ir ratio of1:1supported on CNCs with a high degree of graphitization have an excellent electrocatalytic activity. There may be three reasons for this. Firstly, the alloying of Pt-Ir nanoparticles may modify the surface and electronic structures of Pt, which facilitates the improvement of electrocatalytic activity, especially that for oxygen reduction reaction. Secondly, the use of base metal Ir for alloying is of prime importance. Iridium is a transition metal possessing an excellent stability in acidic media in comparison with other transition metals frequently used for alloying. Such a chemical property could have the advantage in decreasing the dissolution of the alloy and favor the stabilization of the alloy catalyst. Thirdly, using well-graphitized CNCs as the support material would strengthen the interaction between the nanoparticle and support, resulting in an obvious improvement of catalyst durability.