官能基化石墨烯承載核殼 Co3O4@Pt 奈米觸媒之鹼性氧氣還原催化研究

Abstract

本論文分為三大部分，第一部份在於研究如何提升石墨烯表面之含氧官能基團含量，以提升金屬氧化物奈米顆粒於碳載體之分散性與含量；第二部份為合成Co3O4金屬氧化物觸媒於官能基化石墨烯上，以XRD分析表面晶體為Co3O4奈米顆粒，以TEM觀察表面顆粒之形貌與分散性，並以電化學方法檢測官能基化後觸媒催化氧氣還原反應活性之改變；第三部份是利用金屬置換反應形成白金殼結構並以電化學方法分析其對於氧氣還原反應之催化性效能。 在第一部份中的實驗中，將石墨烯懸浮液與Nafion ionomers同時滴於碳布上作為電極使用，並在含氧環境下透過循環伏安法還原生成自由基，破壞Nafion ionomers結構進而在石墨烯表面生成含氧官能基團。利用XPS分析生成官能基團之比例，證實可以利用此簡易電化學方式生成官能基化石墨烯。 在第二部分，將官能基化石墨烯作為碳載體利用水熱法生成Co3O4奈米顆粒，此非貴金屬觸媒於鹼性環境下具有良好之氧氣還原催化活性。並以XRD分析觸媒顆粒，證實合成之奈米顆粒為Co3O4晶體。 在第三部份實驗中，利用氫氣將Co3O4表層部分還原為金屬態之鈷，並低溫浸泡於含有白金離子之溶液中，進而發生置換反應於奈米顆粒表面。利用XRD來檢測不同反應溫度與時間下氫氣還原生成鈷之比例，試圖找出最佳化參數。並以電化學方式檢測Co3O4@Pt/FGN、Co3O4@Pt/GN與Pt/C觸媒於鹼性環境下氧氣還原反應之催化活性。

This thesis research covers three different parts. The first part focuses on increasing the amount of oxidized functional groups on graphene sheets to improve the distribution and loading mass of metal oxide nanoparticles on carbon supports; in the second part, I synthesize Co3O4 electrocatalysts on functional graphene, identifying the nanocrystal by XRD analysis, observing the morphology and distribution by TEM, and measuring the electrocatalytic activity by electrochemical method; in the third part, I utilize a displacement reaction to form platinum shell structure on Co3O4 and analyzing its electrocatalytic activity for oxygen reduction reaction in an alkaline media. Experimentally, in the first part, I mix graphene suspension and Nafion ionomers and dripping onto a carbon cloth serving as a working electrode. Using cyclic voltammetric scans in an environment with oxygen dissolved I am able to form oxidized radicals to decompose Nafion ionomers, resulting in the generation of oxidized functional groups on graphene surface. I estimate the ratio of as-synthesized functional groups by XPS analysis and confirm that this method can successfully produce functional groups on graphene sheets. In the second part, I adopt a hydrothermal method to synthesize Co3O4 nanoparticles on functionalized graphene. From literatures, this Co3O4 exhibits a greater ORR catalytic activity in alkaline medium over that of carbon material. I also utilize XRD analysis to identify the nanoparticles are Co3O4 crystalline. In the third part, I partially reduce the surface of Co3O4 particles to metallic cobalt by a mild hydrogen reduction treatment, and immerse the sample in a Pt electrolyte at 10 to initiate a displacement reaction so Pt is deposited on the surface of Co3O4. I measure the content of cobalt in treated catalysts for different reaction temperature and reaction time, intending to determine the optimized parameters. Subsequently, I analyze oxygen reduction reaction activity and electrochemical surface area for Co3O4@Pt/FGN, Co3O4@Pt/GN and Pt/C in alkaline media using a variety of electrochemical methods.