磁性層狀碲化物之合成與電催化穩定性研究

Abstract

磁場輔助電催化已被視為一種有前景的方法，可提升電化學反應的動力學與選擇性，特別是在能源轉換技術中扮演核心角色的氧化反應（OER）。鐵磁性電極能夠促進自旋極化的電荷轉移與氧中間體的相互作用，從而提升催化效率。儘管如 CoFe2O4 與 NiZnFe4Ox 等材料已展現出在磁場下增強的 OER 活性，然而同時具備強鐵磁性與高催化活性的材料卻相當稀少。 二維（2D）層狀磁性材料因其可調控的磁性與表面特性，提供了一種獨特的解決方案。在眾多材料中，鐵碲基化合物如 Fe3GeTe2（FGT）與 Fe3-xGaTe2（FGaT）備受矚目。這些材料展現出顯著的磁各向異性、高表面反應性，以及範圍從 130 K 至超過 380 K 的居里溫度，成為磁-電催化耦合的理想候選材料。 然而，這些材料在環境與電化學條件下的穩定性尚未被充分理解。有研究指出 FGT 在空氣中會發生降解，亦有報告顯示其在操作環境中具有一定穩定性。本論文旨在探討鐵碲鐵磁材料的磁性、催化性與環境行為，以理解其降解機制，並尋求提升其在 OER 應用中操作穩定性的策略。 本研究採用一種創新的結構同系物方法，系統性地研究 FGT 催化性能的起源及其電化學降解的根本原因。透過合成並表徵 Fe3GeTe2 與其同構類比物 Fe3GaTe2（FGaT），建立一個可直接比較的研究框架，以釐清子層組成對活性與穩定性的影響。結合先進的電化學測量、表面分析技術與密度泛函理論（DFT）計算，本研究揭示電子結構對催化行為的影響，並找出造成材料降解的原子尺度因素。 研究結果顯示，FGT 與 FGaT 的催化活性主要由 Fe 的 3d 軌域所主導，這些軌域調控氧中間體在 OER 過程中的吸附與轉化。此發現解釋了兩種材料在基面上表現出相似的析氫反應（HER）與析氧反應（OER）性能。然而，在長期電化學穩定性方面，兩者表現出顯著差異：FGaT 的降解速度遠高於 FGT。透過 DFT 分析，我們將此不穩定性歸因於 Ga 取代 Ge 所導致的晶格內 Te 原子鍵結強度下降，進而促進表面重構，並在電化學條件下形成非晶或氧化相。 本研究證明了結構同系策略在解耦催化活性與電化學降解方面的潛力，並為設計穩定的磁性電催化材料提供了理性設計準則。藉由明確指出影響性能與降解的電子與結構起源，本論文為未來開發具備最佳催化效率與穩定性的次世代二維鐵磁材料奠定基礎。最終，本研究深化了對自旋相關電催化現象的基礎理解，並為可持續能源轉換技術開創了新方向。

Magnetic-field-assisted electrocatalysis has emerged as a promising approach to enhance the kinetics and selectivity of electrochemical reactions, especially the oxygen evolution reaction (OER), which is central to energy conversion technologies. Ferromagnetic electrodes enable spin-polarized charge transfer and interaction with oxygen intermediates, improving catalytic performance. While materials such as CoFe2O4 and NiZnFe4Ox have shown enhanced OER activity under magnetic influence, these systems must simultaneously possess strong ferromagnetism and catalytic activity—a combination not easily found. Two-dimensional (2D) layered magnetic materials offer a unique solution due to their tunable magnetic and surface properties. Among these, iron-telluride-based compounds like Fe3GeTe2 (FGT) and Fe3-xGaTe2 (FGaT) have attracted attention. These materials exhibit significant magnetic anisotropy, high surface reactivity, and Curie temperatures ranging from 130 K to over 380 K, making them suitable candidates for magnetic-electrocatalytic coupling. However, the environmental and electrochemical stability of these materials remains poorly understood. Reports indicate degradation of FGT in ambient conditions, while others suggest stability under operating environments. This dissertation investigates the magnetic, catalytic, and environmental behavior of iron-telluride ferromagnets, aiming to understand their degradation mechanisms and identify strategies to enhance their operational durability in OER applications. In this thesis, we address this challenge by employing a novel structural homolog approach to systematically investigate the origins of FGT’s catalytic performance and the fundamental causes of its electrochemical degradation. By synthesizing and characterizing Fe3GeTe2 alongside its isostructural analog Fe3GaTe2 (FGaT), we provide a direct comparative framework that isolates the effects of sublayer composition on both activity and stability. Using a combination of advanced electrochemical measurements, surface characterization techniques, and density functional theory (DFT) calculations, we elucidate the electronic structure contributions to catalytic behavior and identify the atomic-scale factors responsible for material deterioration. Our results reveal that the catalytic activity of both FGT and FGaT is predominantly governed by Fe 3d orbitals, which mediate the adsorption and transformation of oxygen intermediates during OER. This finding explains the comparable basal-plane hydrogen evolution and oxygen evolution reaction performances observed experimentally for both materials. However, we find a marked difference in their long-term electrochemical stability: FGaT exhibits significantly accelerated degradation compared to FGT. Through DFT analysis, we attribute this instability to the substitution of Ga for Ge, which weakens the bonding strength of Te atoms within the lattice, thereby facilitating surface reconstruction and the formation of amorphous or oxide phases under electrochemical conditions. These insights establish structural homologs as a powerful strategy to decouple catalytic activity from electrochemical deterioration, enabling more rational design principles for stable magnetic electrocatalysts. By pinpointing the electronic and structural origins of both performance and degradation, this work lays the foundation for engineering next-generation 2D ferromagnetic materials with tailored compositions that optimize both catalytic efficiency and durability. Ultimately, this research advances the fundamental understanding of spin-dependent electrocatalysis and opens new avenues for the development of robust, high-performance materials for sustainable energy conversion technologies.