| 摘要: | 本論文以高分子電解質燃料電池(Polymer Electrolyte Membrane Fuel Cells)為研究主題，並且是特指以質子交換膜為電解質，被認為是淨零碳排最有前景的技術之一的質子交換膜燃料電池(Proton Exchange Membrane Fuel Cells, PEMFCs)。此研究領域中已有許多將鉑基合金奈米顆粒沉積在碳支撐體上，以增加鉑基觸媒的鉑質量比活性與電化學表面積，然而，在實際應用於PEMFC時，鉑質量比活性與電化學表面積的增加往往未能如預期地轉化為質量比功率密度(Mass Specific Power Density, MSPD)的提升，這是由於在燃料電池裝置中有離子、電子和氣體傳輸的限制。為解決這些問題，本研究主要採用了兩種策略。
首先，本研究通過脈衝雷射沉積(Pulsed Laser Deposition, PLD)直接將PtCo3奈米顆粒沉積到作為氣體擴散層(Gas Diffusion Layer, GDL)的碳紙上，形成奈米多孔薄膜觸媒層，提供連續的電子傳輸通路。並且進一步藉由使用掃描連續光雷射處理(Scanning Continuous-Wave Laser Processing, SCWLP)對奈米多孔薄膜進行材料改質，研究中顯示SCWLP同時具有鉑表面離析(surface segregation)與微燒結的效果，能夠使PtCo3奈米顆粒形成富鉑殼的殼核結構，並且將奈米顆粒間的接合強度提升，可以增加PtCo3奈米顆粒堆疊觸媒層的電化學表面積(Mass Specific Electrochemical Surface Area, MSECSA)與耐久性。實際用於PEMFCs時，使用SCWLP與不使用SCWLP相比，MSECSA增加了56%。並且在1大氣壓氧氣下$0.6~V$時的陰極MSMSPD達到8.79 kW g-1，顯著高於使用純鉑的情況(6.06 kW g-1)，並在1.5大氣壓氧氣下達到12.0 kW g-1。
其次，本研究開發滴塗法(drop-casting)，可直接將Nafion沉積在以PLD所製備的鉑奈米多孔薄膜氣體擴散電極上，形成質子交換膜，滴塗Nafion可建立在觸媒層中的質子傳輸網絡來提升電流密度。經由優化Nafion溶液的溶劑組成、乾燥溫度和熱壓條件，與相同厚度的商購膜相比，可使PEMFC之歐姆阻抗降低35%，本研究中的PEMFC電流密度可達1902 mA cm-2@0.6 V，在使用2 atm氫氣與氧氣的情況下，比商購質子交換膜高出21%。
此外，本研究亦使用滴塗法在Nafion質子交換膜中摻雜二氧化鈰奈米顆粒以提升質子交換膜之抗化學降解能力。結果表明摻有CeO2的Nafion膜可顯著提升PEMFC的電流密度，同時提升PEM的耐久性。這種改善歸因於CeO2奈米顆粒可增加水分吸收和膜內質子傳輸的能力，能夠促進更有效的水管理來減少觸媒層的水淹問題。;This thesis focuses on Polymer Electrolyte Membrane Fuel Cells (PEMFCs), specifically Proton Exchange Membrane Fuel Cells, which are considered one of the most promising technologies for achieving net-zero carbon emissions. In this research field, many studies have deposited platinum-based alloy nanoparticles on carbon supports to increase the mass-specific activity and electrochemical surface area of platinum-based catalysts. However, in practical applications of PEMFCs, the increase in mass-specific activity and electrochemical surface area often does not translate as expected into an enhancement of mass-specific power density (MSPD) due to limitations in ion, electron, and gas transport within the fuel cell device. To address these issues, this thesis adopted two main strategies.
Firstly, this study employs Pulsed Laser Deposition (PLD) to directly deposit PtCo3 nanoparticles onto carbon paper, serving as the Gas Diffusion Layer (GDL), forming a nanoporous thin-film catalyst layer that provides a continuous electron transport pathway. Additionally, the study further modified the nanoporous film material using scanning continuous-wave laser processing (SCWLP). The research shows that SCWLP induces both platinum surface segregation and micro-sintering effects, which can form a platinum-rich shell-core structure of the PtCo3 nanoparticles and enhance the bonding strength between nanoparticles. This increases the electrochemical surface area (ECSA) and durability of the $PtCo_{3}$ nanoparticle-stacked catalyst layer. When used in PEMFCs, the ECSA increased by 56% with SCWLP compared to without SCWLP. At 0.6 V under 1 atm of oxygen, the cathode mass-specific power density (MSPD) reached 8.79 kW g-1, significantly higher than that of pure platinum 6.06 kW g-1 and reached 12.0 kW g-1 under 1.5 atmospheres of oxygen.
Secondly, this study developed a drop-casting method to directly deposit Nafion onto the platinum nanoporous thin-film gas diffusion electrodes prepared by PLD, forming a proton exchange membrane. Drop-castied Nafion establishes a proton transport network within the catalyst layer, enhancing current density. By optimizing the solvent composition of the Nafion solution, drying temperature, and hot-pressing conditions, the ohmic resistance of the PEMFC was reduced by 35% compared to commercial membranes of the same thickness. The current density of the PEMFC in this study reached 1902mA cm-2@0.6 V, 21% higher than that of the commercial proton exchange membrane under 2 atm hydrogen and oxygen.
Moreover, this study also used the drop-casting method to dope cerium dioxide CeO2 nanoparticles into the Nafion proton exchange membrane to enhance the chemical degradation resistance. The results show that the Nafion membrane doped with CeO2 significantly improved the current density and durability of the PEMFC. This improvement is attributed to the ability of CeO2 nanoparticles to increase water absorption and proton transport within the membrane, facilitating more effective water management to reduce flooding issues in the catalyst layer. |
