世界人口快速成長與能源大量消耗，導致化石燃料的缺乏和全球溫室效應等問題亟需解決。為了減少溫室氣體的排放，迫切需要可以取代的能源，燃料電池作為一種綠色能源，近年來得到許多發展，歸因於不產生二氧化碳的反應過程。為了開發環境友善以及可持續使用的能源系統，氧氣還原反應 (oxygen reduction reaction, ORR) 是非常重要的反應之一，因此開發能夠有效促使氧氣還原反應的電催化劑至為重要。
對於ORR，“四電子” 的轉移路徑能夠使氧氣還原成水。儘管鉑基材料的催化劑具有最佳的ORR性能，但由於昂貴的成本與稀缺性，使其在應用中仍受到限制。因此，許多研究團隊致力於開發高效能、低成本、以及穩定性佳的替代催化劑方案。其中，過渡金屬系列中的鐵元素，本身資源豐富且成本低廉，常被作為ORR電催化劑的選擇之一。
本研究藉由微波電漿處理電紡絲纖維，製備碳化鐵複合材料 (Fe3C/Fe@C)。將鐵元素修飾於聚乙烯吡咯烷酮 (polyvinylpyrrolidone, PVP) 與聚丙烯腈 (polyacrylonitrile, PAN) 中，利用靜電紡絲製備聚合物纖維，再藉由微波電漿處理還原鐵離子，以取代傳統耗時耗能的熱處理方式。利用場發射掃描式電子顯微鏡、X光繞射分析、以及拉曼光譜儀，對樣本進行分析。為了探討ORR的性能，在電化學的測量中，使用三極式的電解槽與旋轉環盤電極，利用循環伏安法 (cyclic voltammetry, CV) 和線性掃描伏安法 (linear sweep voltammetry, LSV) 在鹼性環境下分析，完成電漿參數最適化。同時探討不同高分子纖維載體對ORR性能的影響，例如高分子的選擇 (PVP vs PAN)、酸洗處理、以及電漿後處理。
研究結果顯示，使用氬氣微波電漿處理，只需要12分鐘的處理時間，施加100 mA的電流、0公分的樣本處理位置，0.5 torr的工作壓力，即可有效地製備Fe3C/Fe@C複合材料。在ORR的性能方面，PVP/Fe(0.2M)-0cm-Ar12具有最佳的結果，其電子轉移數在0.05 - 0.80 V vs. RHE的電位勢能範圍內為3.2 - 3.7，並呈現凹狀曲線。此外，透過氧氣析出反應 (oxygen evolution reaction, OER) 研究其電催化活性，在1.73 V vs. RHE的電位勢能下，電流密度達到10 mA cm-2。因此，本研究展示微波電漿處理在碳化鐵的製備和ORR應用方面的效率以及後續應用的巨大潛力。

The exponentially growth of population relates closely to the energy consumption and generation of wastes in different forms such that lacks of fossil fuels and global greenhouse effects are problems to solve. To reduce the emission of greenhouse gas, the alternative energy source is of urgent need such that fuel cells, one type of green energy, are developed recently due to its environmentally friendly and no generation of carbon dioxide. For the development of green and sustainable energy systems, oxygen reduction reaction (ORR) is one of the important reactions where efficient electrocatalysts are highly desired for application in energy devices.
For ORR, four-electron transfer pathway is desired that, the oxygen can be reduced to the water. Although, the platinum-based catalyst showed the best ORR results, the limits remain due to its high costs and scarcity. Therefore, research groups have dedicated in developing alternative catalysts with highly efficient, low-cost, and stability. Among them, transition metal iron is often selected to prepare carbides for ORR as electrocatalysts because of its abundant and lost cost.
In this study, iron carbide composite (Fe3C/Fe@C) was prepared by microwave plasma treatment on electrospun fibers. The iron elements are introduced into polyvinylpyrrolidone (PVP) and polyacrylonitrile (PAN) and the polymer fibers were prepared by electrospinning. After that, the microwave plasma is applied to reduce iron ions, which can replace conventional time-consuming and energy-intensive thermal treatment. The as-prepared samples are analyzed by field-emission scanning electron microscopy, X-ray diffraction, and Raman spectroscopy to determine its characteristics. To investigate the performance of ORR, the electrochemical measurements are carried out by using three-electrode cell and rotating ring-disk electrode. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) are applied under alkaline environment to optimize plasma parameters. Furthermore, the influence of ORR performance is explored by using different polymers (PVP vs PAN) as fiber carriers, acid leaching treatment, and plasma post-treatment.
The results of this study showed that iron carbide composite (Fe3C/Fe@C) can be effectively prepared by argon microwave plasma treatment in only 12 minutes with 100 mA of applied power, 0 cm of treatment distance, and 0.5 torr of working pressure. For the performance of ORR, PVP/Fe(0.2M)-0cm-Ar12 revealed the best results, which have the number of electron transfer in the range of 3.2 to 3.7 with concave shape under 0.05 to 0.80 V vs. RHE of applied potential. Furthermore, the electrocatalytic activity investigated by oxygen evolution reaction (OER) reported the current density of 10 mA cm-2 under 1.73 V vs. RHE of applied potential. The great potential of microwave plasma treatment for the preparation of iron carbide for the applications of ORR is therefore demonstrated.

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