Research On Lithiated Nickel Oxides As Catalyst Supports For Direct Methanol Fuel Cell

Owing to their good characteristics such as simple structure, high power efficiency and environmental friendliness, direct methanol fuel cell (DMFC) have received a great deal of attention as alternative power sources especially for automobiles and portable electronic devices. At present, platinum is the most common catalyst for DMFC. But many kinds of intermediates generated during electro-oxidation of methanol strongly adsorb on the Pt surface and deteriorate the Pt catalyst. In addition, the price of Pt is high. Both factors limit the large-scale production of DMFC. So, to search for catalysts with high catalytic efficiency and low price is more and more urgent.In this thesis, the literature related to poisoning mechanism and anti-poisoning mechanism of Pt catalyst are reviewed. A novel way to improve the duration of the Pt catalyst is put forward.In view of the bi-functional mechanism, the species which can activate water and form oxygen-containing species can improve the performance of the Pt catalyst. Many high-valence metal oxides can activate water and produce OH_ads, which offers the possibility for replacing noble promoter metals such as Ru Pd by common metals. For these common metals, they should be stable enough to react steadily with water and not to oxidize methanol, resulting in reducing the efficiency of batteries. As well known, the doped lithiated nickel oxides (LiNi_1-xM_xO₂, M = Al, Co, and Mg) are stable and provide high-valence Ni(+3) which can activate water and generate OH_ads. In our lab, we try to use the lithiated nickel oxide (LiNiO₂) and doped lithiated nickel oxides (LiNi_1-xM_xO₂, M = Al, Co, and Mg) as supports for the anode catalyst for DMFC to test their performance.The main work is as follows. Lithiated nickel oxide (LiNiO₂) and doped lithiated nickel oxides (LiNi_1-xM_xO₂, M = Al, Co, and Mg) are synthesized using high temperature solid-state method. Their structure is characterized by XRD technique. XRD patters show that the structure of the doped lithiated nickel oxides is the same as that of lithiated nickel oxide.The stability and electrochemical performance of LiNi_1-xM_xO₂(M = Al, Co, Mg) are measured in 0.5 mol·dm^-3H₂SO₄/0.5 mol·dm^-3H₂SO₄ +1 mol·dm^-3CH₃OH in a conventional three-electrode system. The results obtained from the experiments suggest that the three series of the lithiated nickel oxide (LiNiO₂) and doped lithiated nickel oxides (LiNi_1-xM_xO₂, M = Al, Co, and Mg) are stable enough for support application in DMFC. These experimental results also suggest that the Al-doped samples can catalyze the electro-oxidation of methanol, which may be related to the separate phase of Al₂O₃. LiNi_1-xM_xO₂ doped with Co and Mg though can activate water but can not catalyze electro-oxidation of methanol. This reveals that formation of oxygen-containing species and electro-oxidation of methanol are two separate steps, which strongly backs up the bi-functional mechanism for electro-oxidation of methanol.The morphology of Pt/LiNi_1-xM_xO₂( M = Al, Mg) is characterized using HRTEM. HRTEM images demonstrate that the particles of Pt are very small and well dispersed on the supports. The stability and electrochemical performance of Pt/LiNi_1-xM_xO₂(M = Al, Co, Mg) are measured in 0.5 mol·dm^-3H₂SO₄/0.5 mol·dm^-3H₂SO₄ +1 mol·dm^-3CH₃OH in a conventional three-electrode system. The experiments suggest that the anti-poisoning of the Pt/LiNi_1-xM_xO₂catalyst is much better than those of the other two, while that of the Pt/LiNi_1-xAl_xO₂ is the worst.In the thesis, a new way to improve catalysis performance and stability of Pt catalyst is provided. Researches show that catalysts with the doped high-valence metal oxides can serve as both promoter and catalyst support, help to find the new and efficient and inexpensive catalyst. Therefore, the work in the thesis is important for the theory and practical application.