A Core-Shell Fibrillar Electrocatalyst for the PEMFC Cathode By Microwave Accelerated Galvanic Displacement of Nickel with Platinum

Abstract

Currently Pt/Ni alloy [1] and de-alloyed [2] Pt/Ni nanoparticles, and the 3M nanostructured thin film catalyst of de-alloyed Pt/Ni films on whiskers [3] are some of the few to have met the DoE 2020 mass activity target of 0.44 A/mg Pt at 0.9 VIR free. The origin of the extraordinary activity shown by the Ni/Pt system is attributed to a delicate balance between a thin Pt shell and the sub-surface Ni content [1]. One approach to the preparation of highly active Ni/Pt electrocatalysts is by galvanic displacement of Ni from nanofibres with platinum [4]. We have recently found that is possible to reduce significantly the reaction time for Pt-Ni galvanic displacement by using a microwave-assisted procedure on Ni nanofibres, which leads to high mass activity catalysts (>0.5 A/mg Pt) in only 2 minutes. The shell thickness and density are controlled by extent of Ni/Pt displacement (Pt loading), itself controlled by the concentration of Pt ions in solution. By tuning the Pt content, Pt/Ni core/shell electrocatalysts were prepared that do not require electrochemical etching of surface Ni or de-alloying before utilisation. In addition the nickel core can be leached leaving chemically stable Pt4Ni thin tubular structure.