開發複合式氧化還原電極於電化學選擇性硝酸鹽還原至氨氮回收之研析

Abstract

隨著全球產業的快速發展，資源永續循環已成為當前技術發展的重要目標。其中，氨氮(包含氨氣與銨離子)被視為各產業關鍵的化學原料與未來能源發展的重要載體(Energy carrier)，其需求量隨著科技進步而持續增加。然而，傳統的哈伯法(Haber-Bosch process)製氨技術需消耗大量能源，限制了其永續性。此外，工業活動的快速擴張亦導致大量含高濃度硝酸鹽的廢水排放，對環境與人體健康造成潛在危害。因此，開發具高效率與高選擇性的硝酸鹽還原(Nitrate reduction)技術，以氨氮為主要生成產物並實現其選擇性回收，具有關鍵的重要性。 本研究開發複合式氧化還原電極(Redox composite electrodes)，結合功能性穿透式電極(Functional flow-through electrode)與嵌入式電極(Intercalation electrode)之設計，透過電化學氧化還原機制成功實現選擇性電化學硝酸鹽還原為氨氮，並達到氨氮的選擇性濃縮與回收。本研究的重點首先在於驗證功能性穿透式電極(Flow-through electrode)相較於傳統流經式電極(Flow-by electrode)在電化學硝酸鹽還原反應中的效能提升與反應機制。接著進一步設計改良功能性穿透式電極以實現高效硝酸鹽去除與高選擇性氨氮生成。透過在靜電紡絲活性碳纖維上電鍍金屬銅/氧化銅，藉由控制電鍍時間以調控金屬銅與氧化銅的晶面生長，從而提升硝酸鹽去除速率、氨氮選擇性與氨氮生成速率。此外，本研究結合具金屬有機骨架結構特性的普魯士藍(Prussian blue analogs, PBAs)材料與高導電性奈米碳管(Carbon nanotubes, CNTs)，構築高電化學活性的氧化還原嵌入式電極，以實現水中銨離子的選擇性捕捉。藉由普魯士藍材料金屬有機骨架結構特性，可有效實現銨離子的選擇性電化學捕捉與濃縮。同時，該奈米碳管複合嵌入式電極展現出高導電性與高比電容等優異電化學特性，並具備高中孔比例以促進離子傳輸。 總體而言，本研究將功能性穿透式電極與高電化學活性嵌入式電極引入水處理技術中，成功提升電化學硝酸鹽去除效率並實現氨氮的選擇性生成。同時，透過對銨離子的選擇性捕捉與濃縮，有望達成氨氮資源回收與再利用的目標，展現此技術於永續水資源管理中的應用潛力。

With the rapid development of global industries, sustainable resource circulation has become a crucial goal in modern technological advancement. Among various resources, ammonia, including ammonia gas and ammonium ions, is recognized as a key chemical feedstock for many industries and an important energy carrier for future energy systems, with its demand continuing to rise alongside technological progress. However, the conventional Haber–Bosch process for ammonia synthesis is highly energy-intensive, limiting its sustainability. In addition, the rapid expansion of industrial activities has led to the discharge of large volumes of nitrate-containing wastewater, posing potential threats to both the environment and human health. Therefore, developing an efficient and highly selective nitrate reduction technology that produces ammonia as the primary product and enables its selective recovery is of critical importance. In this study, redox composite electrodes were developed by integrating a functional flow-through electrode and an intercalation electrode, enabling the coupling of electrochemical reduction and oxidation processes to achieve selective electrochemical nitrate reduction to ammonia, as well as selective ammonium enrichment and recovery. The first focus of this research was to elucidate the performance enhancement and reaction mechanisms of a functional flow-through electrode compared with a conventional flow-by electrode in electrochemical nitrate reduction. Furthermore, a functional flow-through electrode was designed to achieve efficient nitrate removal and high ammonia selectivity. By electrodepositing Cu/Cu2O onto electrospun activated carbon fibers and controlling the electrodeposition time to tune the crystal facet growth of Cu and Cu2O, the nitrate removal rate, ammonia selectivity, and ammonia production rate were significantly improved. Furthermore, this study combined Prussian blue analogs (PBAs), which possess metal–organic-framework-like structures, with highly conductive carbon nanotubes (CNTs) to construct a high-electrochemical-activity intercalation electrode for the selective capture of ammonium. The CNT-composited intercalation electrode exhibited excellent electrochemical properties, including high electrical conductivity, high specific capacitance, and a large mesoporous ratio that facilitated ion transport. Additionally, its metal–organic-framework-like (MOF-like) structure enabled selective electrochemical capture and enrichment of ammonium ions. Overall, this study successfully introduced novel functional flow-through electrodes and high-electrochemical-activity intercalation electrodes into water treatment technology, enhancing electrochemical nitrate removal efficiency and achieving selective ammonia generation, as well as selective capture and enrichment of ammonium ions. This work demonstrates great potential for realizing ammonia nitrogen resource recovery and reuse, contributing to sustainable water resource management.