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The Synthesis and Evaluation of Novel Core/Shell Nanoparticles Catalysts

Albalwi, Hanan Abdullah

[Thesis]. Manchester, UK: The University of Manchester; 2016.

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Abstract

This thesis focuses on core/shell nanoparticle catalysts including preparation, characterization and testing performance using direct methanol fuel cell. Core/shell were prepared using noble and non-noble metals. Also some core/ shell nanoparticles supported on silica and different types of carbon were prepared as well in this thesis. Non-noble core/shell nanoparticles including novel Co/Ni, SiO2/Ni using three types of silica and novel SiO2/CoFe were prepared by a new modified sol-gel method using hydrazine in alkali media as the reducing agent to reduce metal chloride through two steps process. Parameters such as temperature, pH of solution and reducing agents, were seen to be of great importance in deciding the morphology of the final product as well as the structure of the core/shell catalyst. Core/shell nanoparticles have been successfully prepared for Co/Ni and SiO2/CoFe for first time by choosing the right parameters. This study presents the unique structure which has not been obtained previously for SiO2/Ni catalyst using commercial silica as core. A novel halo shaped structure was the common feature in the catalysts prepared as indicated by TEM. This study presents as well noble Ru/Pt core/shell nanoparticles supported on three types of carbon by a new modified polyol method for first time. The author of this work is not aware of any studies that have prepared Ru/Pt on carbon powder ≤ 50 nm and Ru/Pt on CMWNT previously. This work presents special structure (crown- jewel shaped) for Ru/Pt on Vulcan XC-72 carbon which was not obtained previously for the same catalyst. Selected catalysts were tested using a direct methanol fuel cell. SiO2/Pt core/shell nanoparticles were prepared for the first time by two different methods, namely a new modified sol-gel and polyol methods with novelty structures halo and crown- jewel shaped respectively. Based on the particles size obtained from TEM images, the modified polyol method seems to have a much greater impact on the particles size than the modified sol-gel method. Based on these findings Ru/Pt, Ru/Pt supported on three different types of carbon and Pt supported on CMWNT were prepared using the new modified polyol method. Pt on CMWNT catalyst was synthesized for the first time successfully by a new modified polyol method and all the particles were found to be well dispersed with a narrow size distribution of an average particles size of 3nm. This catalyst gave promising results on DMFC. Pt supported on CMWNT and Ru/Pt supported on Vulcan and CMWNT were used for the first time as electro-catalysts in DMFC to study the effect of the support on the catalytic activity of catalysts. The results show that Ru/Pt on CMWNT gives better performance than the unsupported Ru/Pt and Ru/Pt on Vulcan XC-72. Using Ru/Pt on CMWNT with higher methanol concentration (anode feed) improved the fuel cell power density when compared with the RuPt commercial catalyst.