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Title:	Sintesis dan pencirian nanotiub karbon terdop nitrogen sebagai mangkin katod untuk aplikasi sel fuel
Authors:	Wong Wai Yin (P54769)
Supervisor:	Wan Ramli Wan Daud, Prof. Dato' Dr. Ir
Keywords:	Nanotiub karbon Sel fuel Fuel cells
Issue Date:	28-Mar-2014
Description:	Kemunculan teknologi sel fuel kebelakangan ini telah mencipta peranti penukar tenaga baru untuk penjanaan tenaga elektrik yang berpancaran sifar, bersih dengan kecekapan yang tinggi daripada tenaga hidrogen. Meskipun demikian pengkomersialannya masih dirintangi oleh kos pembuatan yang tinggi dan ketahanan komponen yang rendah. Bagi menyahut cabaran kos, penyelidikan dan pembangunan intensif sedang giat dijalankan untuk mengganti platinum yang mahal terutama di katod dengan mangkin baru lebih murah yang mengurangkan kos sel fuel. Di samping itu, mekanisme penurunan oksigen pada katod masih tidak diketahui secara jelas. Dalam kajian ini, suatu sebatian organik berstruktur nano yang lebih murah iaitu nanotiub karbon terdop nitrogen (NCNT) telah disintesis dan dicirikan; dan keaktifan mangkinnya dalam penurunan oksigen dikaji. Kaedah pemendapan wap kimia yang mudah digunakan untuk sintesis NCNT dalam relau tiub dengan logam-organo sebagai mangkin pertumbuhan nanotiub. Ferum (II) ftalosianida didapati mangkin terbaik bagi pertumbuhan nanotiub. Tiga bahan pelopor, anilin, etilenediamin dan dietilamin pada berbagai komposisi dalam etanol telah digunakan sebagai bahan tindak balas tambahan untuk meningkatkan tahap pendopan nitrogen dalam NCNT. NCNT yang disintesis dicirikan dengan menggunakan FESEM, TEM, XPS, Raman, voltametri berkitar dan voltametri cakera gelang berputar. Morfologi NCNT dan keaktifan penurunan oksigen didapati berbeza mengikut bahan pelopor. NCNT yang dihasilkan daripada etilenediamin didapati mangkin terbaik bagi tindak balas penurunan oksigen dengan keupayaan permulaan pada +0.6 V vs elektrod hidrogen piawai (SHE). Dua struktur nitrogen dalam NCNT, piridina-N dan piridina-N-oksida telah didapati bertindak sebagai tapak aktif untuk penjerapan oksigen melalui analisis data eksperimen dan pemodelan molekul dengan perisian Material Studio 5.5. Tindak balas penurunan oksigen yang disimpulkan daripada analisis voltamogram, berlaku melalui pemindahan empat elektron secara tidak langsung. Analisis kinetik NCNT yang terhasil daripada etilenediamin telah dijalankan dalam elektrolit asid dan alkali yang meniru keadaan dalam sel fuel membran penukaran proton dan sel fuel alkali. NCNT bertindak aktif dalam elektrolit alkali dengan nilai 3.8 untuk bilangan elektron terpindah (n ≈ 4) dan potensi permulaan yang tinggi pada +0.05 V vs SHE. Dalam elektrolit asid, n = 3.5 sebagai purata diperolehi dengan potensi permulaan pada +0.6 V vs SHE. Kestabilan kinetik NCNT dikaji dalam julat suhu 25°C hingga 70°C. Dalam media alkali, keaktifan NCNT kekal stabil dengan n purata = 3.85 dan potensi permulaan pada +0.10 V vs SHE pada suhu yang tinggi dengan keaktifan paling tinggi n = 3.9 tercapai pada suhu 50°C. Sebaliknya, keaktifan NCNT dalam media asid menunjukkan penurunan selepas mencapai keaktifan maximum n = 3.6 pada 35°C. Mangkin organik tanpa logam NCNT ini didapati aktif secara elektrokimia terhadap tindak balas penurunan oksigen. Justeru itu, mangkin ini boleh digunakan sebagai mangkin baru untuk aplikasi sel fuel terutamanya dalam sel fuel alkali.,The emergence of fuel cell technology in recent years has created new energy conversion devices for the generation of zero emission, clean and high efficiency electricity from hydrogen energy. However, their commercialization is still thwarted by high cost and durability. In order to address the high cost, extensive research and development are undertaken to replace the expensive platinum, particularly on the cathode with new cheaper catalysts that reduce the overall cost of fuel cells. In addition, the complicated oxygen reduction mechanism at the catalysts still remains unclear. In this study, nitrogen-doped carbon nanotubes (NCNT), which are low cost nanostructured organic compounds, were synthesized and characterized; and their catalytic activity in the oxygen reduction reaction was studied. A simplified chemical vapour deposition method was used to synthesize NCNT in a tube furnace using organo-metal compounds as nanotube growth catalysts. Ferum (II) phthalocyanine was found to be the best catalyst for nanotube growth. Three different nitrogen precursors, aniline, ethylenediamine and diethylamine at various compositions in ethanol were used as additional reactants serving as extra nitrogen sources to enhance the doping level of NCNT. The as-synthesized NCNTs were characterized by FESEM, TEM, XPS, Raman, cyclic voltammetry and rotating-ring disc voltammetry. The morphology as well as the oxygen reduction activity of NCNTs was found to vary with their precursors. NCNTs synthesized from ethylenediamine were found to be the best catalysts for the oxygen reduction reaction with the highest onset potential at +0.6 V versus standard hydrogen electrode (SHE). Two nitrogen structures in the NCNTs, pyridinic-N and pyridinic-N-oxides were found to serve as active sites for oxygen adsorption through experimental data analysis and molecular modeling via Material Studio 5.5. The oxygen reduction reaction was deduced from voltamogram analysis to proceed via an indirect four electron transfer pathway. Kinetic analysis of NCNTs made from ethylenediamine was carried out in acid and alkaline electrolytes that mimic proton exchange and alkaline fuel cell environments. The NCNTs were shown to catalyze well in alkaline electrolyte with an average electron transfer number of 3.8 (n ≈ 4) and a high onset potential of +0.05 V vs SHE. In acidic electrolyte, a lower electron transfer number of 3.5 was obtained with onset potential of +0.6 V vs SHE. The kinetic stability of the NCNTs was studied in the temperature range of 25°C to 70°C. In alkaline media, the activity of the NCNTs remained stable with an average n of 3.85 and onset potential of +0.10 V vs SHE at elevated temperature with the highest activity of n = 3.9 obtained at 50°C. In contrast, the activity of the NCNTs in acid media was shown to be reduced after reaching the maximum activity of n = 3.6 at 35°C. This class of non-metal organic NCNT catalysts was shown to be electrochemically active towards oxygen reduction reaction and therefore can be used as the new catalysts for fuel cell applications especially in alkaline fuel cell.,PhD
Pages:	197
Call Number:	TK2931.W646 2014 3 tesis
Publisher:	UKM, Bangi
Appears in Collections:	Fuel Cell Institute / Institut Sel Fuel

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