Download or read book Synthesis and Performance Evaluation of a Carbon based Catalyst for Use in Polymer Electrolyte Membrane Fuel Cells written by Jasmin De Campos and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Polymer electrolyte membrane fuel cells (PEMFCs) are a green technology that can convert chemical energy into electrical energy by reacting oxygen and hydrogen to form water. One major limitation to their large-scale production is the cost of the platinum catalyst, an expensive precious metal. This project looks into altering the catalyst support structure to reduce the platinum required for a certain performance level and thus ultimately decreasing the high PEMFC catalyst costs.Carbon nanotubes (CNTs) are promising as an alternate catalyst support structure due to their high electrical conductivity, large surface areas, and stability under PEMFC operating conditions. In this project, CNTs were first grown onto stainless steel mesh substrates with chemical vapor deposition (CVD) using a "direct-growth" approach. They were then functionalized with oxygen (fCNTs) by plasma enhanced CVD (PECVD) to improve their hydrophilicity to achieve stable catalyst ink dispersions. Lastly, platinum was deposited (Pt-fCNTs) using pulsed laser ablation (PLA), which has been shown to provide homogeneous dispersions of platinum particles with an average size of 3.6 nm and no agglomeration. This final Pt-fCNT material was then prepared for electrochemical testing in rotating disk electrode (RDE) and PEMFC studies. It was also compared to an industry standard catalyst of platinum on carbon black. An additional study was done wherein various quantities of graphene nanoflakes with oxygen functionalization (GNFs) were added to the Pt-fCNT catalyst inks, dubbed GNF-Pt-fCNT samples, to see if their stability could improve overall performance.Pt-CNT samples with different platinum deposition times underwent thermogravimetric analysis (TGA) to find their weight percent content of platinum. Samples with 5, 10, and 30 minutes of platinum deposition contained 3.1 % of residue and 3.6 %, 4.0 %, and 16 % of platinum respectively.RDE studies were performed focusing on the oxygen reduction reaction, the rate-limiting cathodic PEMFC reaction. Four main conclusions were made: i) samples without platinum showed effectively no activity, ii) all GNF-Pt-fCNT samples made with varying ratios of the carbon materials underperformed compared to the commercial or 5-minute Pt-fCNT sample, iii) Pt-fCNT performance did not correlate with platinum weight content, and iv) 5-minute Pt-fCNTs out-performed the commercial catalyst by approximately a factor of 2.Due to the high mass requirements for PEMFC testing, less samples were tested: 30-minute Pt-fCNTs, GNFs mixed with 30-minute Pt-fCNTs in a 1:1 mass ratio, a commercial catalyst, and plain CNTs. The four main conclusions made were i) the plain CNTs once again showed no activity due to a lack of platinum, ii) GNF-Pt-fCNTs underperformed compared to other platinum containing samples, likely due to GNFs hindering the catalyst layer's conductivity and access to catalytic sites, iii) the Pt-fCNTs behaved similarly to the commercial catalyst at higher potentials suggesting similar reaction kinetics at play, and iv) Pt-fCNTs underperformed compared to the commercial catalyst at potentials lower than 0.8 V, suggesting higher ohmic resistances and mass transport limitations of the support material.A mass study was performed on the synthesis and powder collection processes to understand the yields and practicality of the methodologies used. On average, sonication was able to collect only 31 % of the sample synthesized on the mesh. Additionally, the powder collection method for the various samples had a relatively high yield of 82 % with extremely large standard deviations despite identical preparation conditions for the powders. " --
