理學院: 化學研究所指導教授: 陳浩銘許家碩Hsu, Chia-ShuoChia-ShuoHsu2017-03-022018-07-102017-03-022018-07-102016http://ntur.lib.ntu.edu.tw//handle/246246/271956電催化水分解產氫為解決能源問題的方法之一，然而電解水過程中陽極的產氧反應具有相對較高之過電位，如能有效地減少產氧反應之過電位便能增加水分解之效率；貴金屬氧化物為目前已知最好的催化材料，然而因其高成本而無法被廣泛利用，因此第一列過渡金屬氧化物常作為貴金屬氧化物之替代材料，其中又以尖晶石結構具有較高之穩定性而被廣泛研究。本研究主要是利用不同過渡金屬置換尖晶石結構中的二價金屬位置進行電催化水分解產氧反應，藉由不同過渡金屬的催化活性差異來了解尖晶石結構的催化機制，當機制確立時能更有效的作為增進材料催化活性的依據。 在本實驗中以磁鐵礦( Fe3O4 )為基礎，將四種不同過渡金屬(錳、鈷、鎳、鋅)置換二價金屬，利用X光繞射光譜確立所有雙金屬氧化物皆為尖晶石結構，同時利用同步輻射X光吸收光譜確定大部分二價金屬都位於八面體中心，再透過高解析穿透式電子顯微鏡觀測所有樣品，確定成功地將其五種材料均合成均勻之單晶奈米方塊，藉以確立為單一晶面之催化。電催化產氧反應活性之探討利用電化學儀器測量循環伏安法、線性掃描伏安法、電化學阻抗譜與安培法測得各個材料之氧化行為、過電位與電荷轉移電阻，同時測量伽馬相的三氧化二鐵(γ-Fe2O3)作為三價金屬的比較依據，而結果觀測到二價金屬以鈷跟鎳所取代之氧化物催化活性表現高於其他三者，並配合材料反應前後之氧元素X光吸收光譜，發現其二者催化行為和其他金屬氧化物不同，再更進一步以臨場(in-situ) X光繞射光譜觀測到鈷鐵氧化物及鎳鐵氧化物在產氧反應過程中有羥機氧化物(MOOH)的結構生成，而於二價金屬為錳、鐵及鋅的氧化物與三氧化二鐵皆無此現象發生，因此在進行電催化產氧反應的過程中，羥基氧化物是否產生為決定催化活性的一大因素，而在尖晶石結構中二價金屬如能產生相轉換便可以有效地提升產氧反應之效率。Metal oxide of spinel family has performed great potential to replace RuO2 or IrO2 toward oxygen evolution reaction (OER), but the fundamental mechanism of spinel oxides is still far from a complete understanding especially for the role of metal ions. Owing to various coordinated sites of divalent/trivalent metals ions and surface condition (mor-phology and defects), it’s a great challenge to have a fair assessment of electrocatalytic performance of spinel system. Herein, we demonstrated a series of MFe2O4 (M = Mn, Fe, Co, Ni, Zn) family with a well-controlled morphology to achieve comprehensive study of electrocatalytic activity toward OER, in which most of the divalent metals (M2+) of MFe2O4 were located at octahedral sites and well-defined single-crystal nanocubes were synthesized to minimize the influence caused by crystallographic sites/morphology of variables for each samples. The effects of M2+ ion in MFe2O4 can be realized through investigating the OER behaviors of MFe2O4 and that of γ-Fe2O3 as a reference to have in-depth understanding of the roles of divalent/trivalent metal ions. In-situ X-ray diffraction and ex-situ X-ray absorption spec-troscopies were employed to provide direct evidence that the superior OER activities of CoFe2O4 and NiFe2O4 samples could be attributed to a remarkable phase transformation forward metal oxyhydroxide, while the rest of compounds remain unchanged during oxygen evolution reaction.6729029 bytesapplication/pdf論文公開時間: 2018/8/26論文使用權限: 同意有償授權(權利金給回饋學校)產氧反應臨場X光繞射尖晶石結構Oxygen evolution reactionin-situ XRDspinel structurethesis10.6342/NTU201602981http://ntur.lib.ntu.edu.tw/bitstream/246246/271956/1/ntu-105-R03223169-1.pdf