| 摘要: | 析氫反應（hydrogen evolution reaction, HER）是電解水中不可或缺的半反應，然而其低的轉換效率和緩慢的動力學限制了實際應用，因此開發合適的觸媒以降低 HER的過電位勢在必行。白金(Pt)基觸媒為最常見的HER材料並有著很好的活性，然而其效能在鹼性電解液中相較於酸性電解液差，為了開發具高效能、長時間穩定度與具成本效益的非 Pt 觸媒，具有和Pt相似之氫鍵強度且價格相對較低的釕 (Ru)，可被視作 HER 的次佳選擇，特別在非酸性環境中的應用。另一方面，碳基材因其良好的導電性和實惠的價格而被廣泛地作為觸媒的載體，而與傳統的碳黑相比，具有更高的比表面積和更高的導電性之新興碳載體如類沸石咪唑骨架結構(zeolitic Imidazolate Framework, ZIF)也是一種具未來性的載體材料。
本研究的第一部分透過濕式化學法成功將近乎相同量的 Ru負載於不同的載體，包括 ZIF、多孔碳(PC)、活性碳(AC)和石墨烯(Gr)作為 HER 之觸媒。形貌、相、結晶度、化學組態、局部電子結構和電化學結果顯示Ru/ZIF在所製備的樣品中具有較低的過電位和較大的電化學活性面積，其載體中部分未完全氣化的鋅可作為犧牲劑以防Ru氧化，進而提高 HER的活性。
在第二部分中為得到更好的效能，對ZIF上之Ru負載量進行優化，顯示有效的表面Ru顯著地降低過電位和塔弗(Tafel)斜率。 隨後在酸性電解質中進行去合金法並調整時間，其不僅可修飾表面也提高了觸媒的HER活性。根據穿透式電子顯微鏡(TEM)之結果顯示此易於調控之後處理可成功地改變Ru於載體上的分散性，進而降低過電位。此外在經由穩定度測試後，經去合金後的樣品其粒徑仍不變，而過電位略微衰減，均表明其在鹼性電解液中仍能保持穩定性。本研究結果顯示將Ru嵌入適合的載體並經由簡單的後處理法是具潛力且能在HER中取代 Pt的材料。;The hydrogen evolution reaction (HER) is an essential half-reaction of electrochemical water splitting while its low conversion efficiencies and sluggish kinetics restrict the practical applications. The development of suitable electrocatalysts employed to lower the overpotential of HER is imperative. Pt-based catalysts are the most common materials and show great HER activity. However, in alkaline medium, its performance is relatively low compared to that in acid. In order to develop Pt-free catalysts with high efficiency, long-term stability, and cost-effectiveness, ruthenium (Ru) with similar hydrogen bonding strength with Pt and relatively low price can be regarded as the second best option for HER, especially in non-acidic environments. On the other hand, carbon matrices have been widely used as the supporter for electrocatalysts due to their great conductivity and affordable price. In contrast to the conventional carbon black, novel carbon support such as zeolitic imidazolate framework (ZIF) with higher specific surface area and greater conductivity is also a promising host material.
In the first part of this study, different host materials with nearly the same Ru loading, including ZIF, porous carbon (PC), activated carbon (AC) and graphene (Gr), have been successfully synthesized via wet chemical method and applied as HER catalysts. The morphologies, phases, crystallinity, chemical states, local structures and electrochemical results show that Ru/ZIF possesses relatively low overpotential and larger electrochemical surface area among the as-prepared samples. The incomplete gasification of zinc from the host material might partially serve as the sacrificial agent in Ru/ZIF and prevent Ru from oxidation, which can boost the HER activity.
Secondly, in order to obtain better performance, the Ru loading on ZIF has been optimized, suggesting that efficient surface Ru apparently lowers the overpotential and Tafel slope. The dealloying step is then conducted in acidic electrolyte with different durations, which not only modifies the surface but also improves the HER activity of the catalysts. Based on the TEM results, it is believed that this easy-to-control post-treatment can successfully change the dispersion of Ru on the support to decrease overpotential for HER. Furthermore, after the stability test, the slight decay of overpotential indicates that the dealloyed samples with unchanged particle size can remain durability in alkaline media. Our results demonstrate that the post-treated Ru embedded on suitable host material is a promising Pt substitute for HER. |
