應用於質子交換膜型燃料電池陰極之鉑合金觸媒製備及其性能研究

Preparation and characterization of Pt-based cathodic catalysts for PEMFC

謝昀紘(Yun-Hung Hsieh)

指導教授 ： 彭宗平

國立清華大學/工學院/材料科學工程學系/碩士(2009年)

https://doi.org/10.6843/NTHU.2009.00410

摘要

本實驗係研究以鉑、釕和鈷三種金屬元素所形成之合金作為質子交換膜燃料電池陰極觸媒，觸媒的合成是以化學還原法直接將鉑合金還原在奈米碳管上，使用硼氫化鈉作為還原劑，鉑釕原子莫耳比固定為4:1，加入鈷金屬藉以提升此觸媒在陰極氧氣還原反應之效率。
　　觸媒的擔體則選擇以多壁奈米碳管作為自製觸媒之擔體，但未施予任何表面處理之多壁奈米碳管其表面結構較為完整，觸媒不易沉積分布在碳管表面，因此，乃藉由硝酸和硫酸與奈米碳管反應俾在奈米碳管表面產生缺陷或有機官能基，使觸媒較易沉積分布在奈米碳管表面。經表面修飾之奈米碳管其物化性質藉由比表面積測試儀、拉曼光譜儀和傅立葉轉換紅外線光譜儀來分析。所有觸媒的組成和性質則藉由X光繞射儀、穿透式電子顯微鏡、感應耦合電漿質譜儀、循環伏安法和膜電極組測試來分析。
　　結果顯示，所有鉑合金奈米粒子都可藉由硼氫化鈉成功地還原，但是，除了鉑釕鈷合金之外的奈米粒子都會聚集在奈米碳管表面缺陷處。鉑釕合金和鉑釕鈷合金的顆粒大小在4 nm左右。在單電池效率測試結果顯示，商用電極具有較高之效率(0.33W/cm2)，自製之鉑釕合金(pH=10)和(pH=11)觸媒電極之效率分別為0.21W/cm2和0.19W/cm2，自製之鉑金屬和鉑釕鈷合金之效率都低於0.05W/cm2。這些觸媒效率的差異可能係由合金之顆粒大小、分散性和合金中鉑金屬的含量等因素所造成。在以下全文中將會討論到自製觸媒之特性以及各種分析結果。

關鍵字

PEMFC ； Pt-based alloy ； NaBH4

並列摘要

A series of Pt-based alloys consisting of Pt, Ru and Co were used as cathodic catalysts for proton exchange membrane fuel cell (PEMFC). The catalysts were synthesized and deposited on multiwalled carbon nanotubes (MWCNTs) directly by chemical reduction using NaBH4 as reducing agent. The atomic ratio of Pt and Ru was fixed at 4:1. By adding Co to the alloy, it was expected that the performance of catalysts in the cathodic oxygen reduction reaction may be improved.
MWCNTs were used as the support of catalysts. However, the original surface was inert and not easy to be deposited with catalysts. By reaction with HNO3 and H2SO4, the surface of MWCNTs could generate defects or organic functional groups so that catalysts could be deposited and dispersed on the surface. The physical and chemical properties of modified MWCNTs were analyzed by BET, Raman, and FTIR. The composition and properties of all catalysts were analyzed by XRD, TEM, ICP-MS, CV, and MEA test.
The result shows that all of the Pt-based nanoparticles except the Pt4Ru1Co5 could be prepared by reduction with NaBH4 and they all aggregated on the surface defects of MWCNTs. The particle sizes of Pt4Ru1 and Pt4Ru1Co5 catalysts were both around 4 nm. The maximum output powers of Pt4Ru1/CNT (pH=10) and (pH=11) were 0.21 W/cm2 and 0.19 W/cm2, respectively, while that of E-TEK was 0.33 W/cm2. The maximum powers of Pt/CNT and Pt4Ru1Co5/CNT were both below 0.05 W/cm2. The difference of performance may result from the dispersion of particles, particle size, and the Pt content in the catalysts. The characterization and analyses of all home-made catalysts are also discussed.

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