| 摘要: | 直接甲醇燃料電池具有高能量密度、燃料穩定容易儲存、填充方便等優勢，相當具發展潛力，由於觸媒催化效率不良，使成本居高不下。觸媒催化效率低，原因包含(1)甲醇氧化與氧氣還原反應步驟複雜，需克服相當高之活化能，因此反應速率低；(2)反應過程中間產物毒化Pt；(3)觸媒金屬在載體上分散與吸附不良、金屬穩定度不足經過使用後，金屬流失或是聚集。 在本論文第一目標以聚苯胺(Polyaniline,PANi)包覆碳奈米管(CNT)與經研磨過活性碳(ACg)表面之PCNT與PACg奈米複合物以及以聚苯胺、聚咇咯(Polypyrrole, Ppy)與聚噻吩(polythiophene, Pth)包覆Vulcan XC-72表面之P1X, Ppy1X與Pth1X奈米複合物為直接甲醇燃料電池陽極觸媒之載體以提昇觸媒催化活性、穩定性與使用壽命。而本論文第二目標為藉由調控不同反應溫度將鉑鉛合金承載於ACg與P1CNT製備出一高氧還原活性與抗腐蝕之鉑鉛合金觸媒。所有陽極觸媒均以錋氫化鈉為還原劑之化學還原方式將鉑釕(Pt-Ru)合金奈米顆粒承載奈米複合物表面。 以聚苯胺所形成奈米複合物為載體之陽極觸媒較聚咇咯與聚噻吩之奈米複合物的觸媒擁有高甲醇催化能力。聚苯胺包覆不同型態碳材之奈米複合物為載體之觸媒中以PtRuP1CNT觸媒展現最佳的甲醇氧化能力，這是來自碳奈米管本身的1D結構容易形成3D的多孔隙的觸媒層架構而增加白金的活性位置與提高甲醇與二氧化碳傳的傳送、排除。 鉑鉛合金觸媒對氧還原反應為4電子反應機制可避免反應中產生過氧化氫(H2O2)而危害電極壽命，且整個氧還原反應為一級反應。PtPbACg_110在加速老化測試(Accelerated Degradation Test, ADT)，多圈式循環伏安法，顯示高度的觸媒穩定性包含了低ECSA變化率與碳腐蝕變化率。 在論文研究中提供利用簡單高分子包覆碳材的載體修飾觀念以提昇觸媒的CO抗毒化、甲醇氧化催化活性以及穩定性。本研究中發現聚苯胺不僅可以抑制顆粒聚集與穩定觸媒亦可以增加觸媒的長時間穩定。而鉑鉛雙合金是具有潛力的新PEMFC與DMFC陰極觸媒金屬。 Direct methanol fuel cells (DMFC) shows potential as a new energy source due to its relatively high energy density, easy to store, transport, and reload. However, the low catalyst efficiency, insufficient durability and high manufacture cost are hurdles for immediate commercialization. The first aim of the research covered in this thesis was to improve the catalytic activity and to extend catalyst durability by using polyaniline (PANi) coated on both carbon nanotube (CNT) and ground active carbon (ACg) surface to form PCNT and PACg nanocomposites, and later we examine the different effects of polyaniline, polypyrrole, and polythiophene coating on Vulcan XC-72 to form P1X, Ppy1X and Pth1X nanocomposites as the anode catalysts supports for direct methanol fuel cell. A second part of the study was to examine a novel cathode catalyst, PtPb alloy, which exhibited high activity and tolerance corrosion in acid media. All the anode electrocatalysts were prepared by depositing Pt-Ru alloy nanoparticles on nanocomposites surface through borohydride reduction. The alloying Pt-Pb nanoparticles were supported on ACg and P1CNT by a mild reduction procedure under temperatures below 200oC. Using polyaniline coating on Vulcan XC-72 as the support to form anode catalyst yielded methanol oxidation catalytic activity higher than polypyrrole and polythiophene nanocomposites catalysts. In comparison, the polyaniline coating on different the type carbon supports, the PtRuP1CNT showed highest methanol oxidation performance due to P1CNT formed 3D porous framework catalyst layer, afforded more active sites and easier transport of methanol and CO2. The platinum-lead alloys tended to follow mainly a 4-electron mechanism, which implied reduced H2O2 formation and first order with respect to the dissolved oxygen. PtPbACg catalyst showed high stability including low ECSA change ratio and carbon corrosion under consecutive scan in 0.1 M HClO4. In summary, present study demonstrated that the PANi coating prevented aggregation, loss of Pt particles, and thereby improved long-term stability of fuel cell catalysts on both anode and cathode. It also unveiled a new design of more durable catalysts by coating conducting polymer layer on carbon support which improved catalytic activity, CO tolerance and stability over other catalysts based on the current method technique. PtPb binary alloy nanoparticles could be used as a new potential cathode catalyst metal for both PEMFC and DMFC |
