氮化鎢作為電催化劑用於氮氣還原合成氨之研究

Abstract

氨的生產是全球肥料工業的重要組成部分，目前主要依賴哈伯法，這種傳統方法在高溫高壓下運作，導致大量能源消耗和二氧化碳排放。相比之下，電催化氮氣還原反應（NRR）提供了一種極具前景的替代方案，能夠在常溫常壓條件下合成氨，同時顯著降低能源的消耗。近年來，NRR研究領域取得了重大進展，科學家們探索了各種電催化劑，包括單原子催化劑（SACs）、過渡金屬氧化物（TMOs）、碳化物（TMCs）、硫化物（TMSs）和氮化物（TMNs）。值得注意的是，TMNs中的原生氮缺陷，例如在MoN、VN和CrN中所觀察到的，可以透過Mars-Van Krevelen機制作為具有潛力NRR活性位點。這些發現為開發高效的氮氣還原反應催化劑開闢了新的研究方向。 本研究著重於系統性地探討立方相氮化鎢（WN）作為NRR電催化劑的潛力，其中，採用反應性磁控濺鍍技術在Si（100）基板上沉積WN薄膜，並透過X-ray繞射（XRD）、X-ray光電子能譜（XPS）和能量散射X-ray分析（EDX）等技術對薄膜進行特性分析。這些分析方法不僅能夠提供薄膜的結構和組成訊息，還能深入了解其表面化學狀態，對於理解催化性能至關重要。 在研究過程中探討了沉積參數，例如氮氣與氬氣的比例和生長溫度，對於W/N化學計量比和NRR催化活性的影響。透過控制這些參數，能夠調節WNx薄膜的化學組成，從而優化其電催化性能。特別值得一提的是，本研究發現，透過在氮氣氬氣流量比例為3的條件下濺鍍所製備出的WN相薄膜，較W2N對於產氨具有更佳的法拉第效率。除此之外，透過通入微量的氧氣，使薄膜中掺雜微量的氧原子，亦能製備出WN相薄膜，並且顯著地提昇了電催化的法拉第效率。 本研究突出了磁控濺鍍技術在製備氮化物作為NRR電催化劑的優勢，展示了對元素組成的精確控制能力。與傳統的溶膠凝膠法相比，磁控濺鍍提供了更高的可重複性和更精確的組成成分控制，這對於開發高效能的催化材料至關重要。此外，還探討了WN薄膜的穩定性和耐久性，這是實際應用中的關鍵因素，透過長時間的電化學測試和表面分析，為未來的材料優化提供了重要依據。

Ammonia production, a crucial component of the global fertilizer industry, currently relies heavily on the Haber-Bosch process. This traditional method operates under high temperature and pressure conditions, resulting in substantial energy consumption and carbon dioxide emissions. In contrast, the electrocatalytic nitrogen reduction reaction (NRR) offers a promising alternative, enabling ammonia synthesis under ambient conditions while significantly reducing energy input. Recent years have seen significant advancements in NRR research, with scientists exploring various electrocatalysts, including single-atom catalysts (SACs), transition metal oxides (TMOs), carbides (TMCs), sulfides (TMSs), and nitrides (TMNs). Notably, native nitrogen-vacancy defects in TMNs, such as those observed in MoN, VN, and CrN, have shown potential as active sites for NRR via the Mars-Van Krevelen mechanism. These findings have opened new avenues for developing efficient nitrogen reduction reaction catalysts. This study focuses on the systematic investigation of cubic tungsten nitride (WN) as an NRR electrocatalyst. WN thin films were deposited on Si (100) substrates using reactive magnetron sputtering and characterized through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray analysis (EDX). These analytical methods provide crucial information about the film's structure, composition, and surface chemical states, essential for understanding catalytic performance. The research explored the impacts of deposition parameters, such as the N2/Ar ratio in the sputtering atmosphere and growth temperature, on W/N stoichiometry and NRR catalytic activities. By controlling these parameters, the chemical composition of WNx thin films could be tuned, optimizing their electrocatalytic performance. Notably, this study found that WN phase thin films prepared by sputtering at higher N2/Ar ratios in the sputtering atmosphere exhibited better Faradaic efficiency compared to the W2N phase. Furthermore, introducing trace amounts of oxygen during deposition resulted in oxygen-doped thin films and significantly enhanced the electrocatalytic Faradaic efficiency. This work highlights the advantages of magnetron sputtering in preparing nitride-based NRR electrocatalysts, showcasing precise control of elemental compositions. Compared to traditional sol-gel methods, magnetron sputtering offers higher reproducibility and more precise composition control, crucial for developing high-performance catalytic materials. Additionally, the stability and durability of WN thin films were investigated, key factors for practical applications. Long-term electrochemical testing and surface analysis provided important insights for future material optimization.