Carbon nanofiber supported Pt nanoparticles with an accurate size control through copolymer stabilization and chemical reduction for PEM fuel cell application
Mahdieh Shakoori Oskooie
Master thesis
Thesis Jury:
Dr. Serkan Ünal (thesis advisor), Dr. Serap Hayat Soytaş (thesis co-advisor), Dr. Selmiye Alkan-Gürsel, Dr. Fevzi Ç. Cebeci, Prof.Dr. Hüseyin Deligöz.
Date & Time: 31 July, 2017– 09:00 A.M.
Place: SUNUM G111
Keywords: Copolymer, electrospinning, platinum catalyst, carbon nanofiber, carbon nanotube, PEM fuel cell
Abstract
A one-pot microwave-assisted synthesis method was developed to produce scalable carbon nanofiber (CNF) supported platinum nanoparticle catalysts through an in-situ polymer-based technique. CNF-supported Pt samples were synthesized through electrospinning of poly(acrylonitrile-co-N-vinylpyrrolidone) (P(AN-co-nVP)) copolymer containing PtCl2 salt and consequent microwave reduction within hydrazine hydrate solution and carbonization. The aim of this study was to achieve a precise control on the size and distribution of the Pt nanoparticles by benefiting from a copolymer random templating and rapid microwave reduction. Prior to the application of microwave reduction on nanofibers, the pure effect of various carbonization temperatures (from 600 ̊C up to 1000 ̊C) on growth of Pt particles was studied. The carbonization at 800 ̊C was observed to represent a homogenous particle size distribution and the highest electroactive surface area (ECSA). Two types of samples were synthesized using microwave-assisted reduction – CNT-free and CNT-containing. The microwave irradiation for various time intervals (15s – 120s) was applied on both the CNT-free and the CNT-containing electrospun nanofibers with PtCl2. By selectively changing the process conditions, the minimum average size of 1.751 nm in diameter was obtained in the case of CNT-free samples while 0.862 nm nanoparticles with a narrow size distribution was achieved for the CNT-containing samples for the first time. The mean Pt particle size was increased as a function of microwave irradiation time. The ECSA values obtained for CNT-free samples demonstrated a maximum activity for sample treated for 30 s, despite the smaller Pt particle size in the 15 s-treated sample. This behavior was attributed to the lower amount of accessible Pt particles on the fiber surface. In the case of CNT-containing samples the best catalytic activity (82.55 m2g-1) was observed for 15s microwave reduction, which was hypothesized to be as a result of the significantly higher number of Pt cluster nucleated near the surface of the CNFs, a higher surface area due to the presence of CNTs and a higher electrical conductivity.