二維碳化鉬結合有機金屬骨架衍生之過渡金屬複合材料 作為雙效電催化水分解觸媒

Abstract

本論文旨在討論利用普魯士藍類似物與二維碳材碳化鉬所衍生之過渡金屬複合材料，於電催化水分解之產氧及產氫反應的應用及效能探討。依照材料的設計面向可分為兩部分，第三章將鈷鐵雙金屬的普魯士藍類似物原位生長在二維碳化鉬層狀上，並調節高溫磷硫化反應溫度轉換為氮摻雜磷硫化鈷鐵之複合材料，應用於電催化水分解反應；第四章則延伸鈷鐵普魯士藍類似物/二維碳化鉬之催化特性，利用水熱生長及高溫磷化的方式形成具有氮摻雜之磷化鎳鈷鐵的複合碳材，應用於電催化水分解反應。 在第三章中，本研究將鈷鐵雙金屬普魯士藍類似物原位生長在二維碳化鉬上，並以此作為前驅物，經由一步磷硫化的方式成功製備了鈷鐵雙金屬磷硫化物複合材料。二維碳化鉬具有良好的產氫反應催化活性、優良的導電性及親水性，目前僅有少數論文利用其性質設計複合材料應用在電催化水分解反應。由於二維碳化鉬表面豐富的帶電官能基能使對應的金屬離子經由庫倫靜電力吸附在其表面，形成均勻的成核點，有助形成二維碳化鉬承載普魯士藍類似物的複合結構。藉由合成出鈷鐵普魯士藍類似物原位生於二維碳化鉬，可經由適度的磷硫化反應衍伸出磷硫化鈷鐵生長於二維碳化鉬之複合結構，從而有效促進電子轉移效率並產生更多活性位點，有利於提升產氧及產氫反應的電催化能力。因此，本研究合成出的磷硫化鈷鐵/二維碳化鉬觸媒具有出色的電催化表現，在鹼性條件下達到10 mA cm-2的電流密度之產氧及產氫反應的過電位分別僅需240及146 mV，且於全水分解二極式系統中，在10 mA cm-2的電流密度下之驅動電壓為1.64 V，並在長期穩定性測試中皆可維持至少120小時的產氧及產氫反應電催化活性。此實驗結果展示了二維過渡金屬碳化物複合普魯士藍類似物衍伸之材料於於電催化產氧及產氫反應觸媒開發的潛力及有效性。 在第四章中，本研究闡釋第三章所提出之鈷鐵普魯士藍類似物/二維碳化鉬複合結構可作為合適的前驅物以衍生出三元過渡金屬磷化物。藉由水熱法使鎳跟普魯士藍類似物內部中的鈷跟鐵金屬反應，從而自普魯士藍類似物結構延伸出鎳鈷鐵氫氧化物的片狀結構，有助於與電解液之間的分子和離子傳輸，並透過磷化處理製備出生長於二維碳化鉬上的磷化鎳鈷鐵維階結構，進而增加活性位點及優化於產氧及產氫反應的電化學表現。本研究中也進一步說明鎳添加量所帶來的片狀結構生成影響及對應的三元過渡金屬磷化物對於電催化產氧及產氫反應效能的重要性。得益於特殊的型貌及化學組成的優勢，本研究合成出的磷化鎳鈷鐵/二維碳化鉬觸媒顯示出極佳的電催化效能，在鹼性條件下，達到10 mA cm-2的電流密度之產氧及產氫反應的過電位分別僅需219及92 mV，且於全水分解二極式系統中，在10 mA cm-2的電流密度下之驅動電壓為1.55 V，並在長期穩定性測試中皆可維持至少120小時的產氧及產氫反應電催化活性。此實驗結果展示了以形貌與組成的面向去調節普魯士藍類似物/二維過渡金屬碳化物衍伸物的電催化特性，且優化後的磷化鎳鈷鐵/二維碳化鉬觸媒極俱應用於電催化水分解反應的可行性。 根據第三章與第四章的核心概念，普魯士藍類似物可與二維碳化鉬結合形成複合結構，並藉由磷硫化、磷化、金屬組成及形貌設計等的方式延伸出各式各樣的過渡金屬複合材料。本論文所提出的研究方向能提供一個平台來設計電催化觸媒或優化其於相關的能源應用領域的催化效率。

This thesis aims to discuss the potential of Mo2C MXene boosted Prussian blue analogues (PBAs) derived transition metal composites toward oxygen evolution reaction and hydrogen evolution reaction of electrocatalytic water splitting. The thesis is mainly divided into two parts, namely, two-dimensional molybdenum carbide (MXene) boosted cobalt iron phosphorus trisulfides for electrocatalytic overall water splitting (Chapter 3) and Prussian blue analogues derived Ni-CoFeP augmented by two-dimensional molybdenum Carbide (MXene) for bifunctional electrocatalytic water splitting (Chapter 4). In Chapter 3, CoFe PBA was in-situ incorporated with two-dimensional molybdenum carbide (Mo2C) MXene, serving as a starting material to yield bimetallic CoFe phosphorous trisulfide on Mo2C by one-step phosphorization and sulfurization. Mo2C possesses good HER electroactivity, excellent electrical conductivity, and hydrophilic nature. To date, there are only a few attempts to fabricate efficient electrocatalysts based on the features of Mo2C with favorable bifunctionalities for water splitting reactions. The abundant polar functional groups on Mo2C will adsorb metal ions via electrostatic attraction to form nucleation sites, making MXene to be amenable to the direct growth of CoFe PBA. The MXene achored CoFe PBA was in-situ transformed into cobalt iron phosphorous trisulfide on MXene (PS3-CoFe/MXene) by proper phosphorization and sulfurization treatment, which can speed up electron transfer characteristic and provide abundant electroactive sites during catalytic processes, leading to improved electrocatalytic performances toward OER and HER. In alkaline solution, the as-synthesized PS3-CoFe/MXene demonstrates prominent HER and OER activities with overpotentials of 146 mV and 240 mV, respectively, at 10 mA cm-2. When applying as bifunctional electrocatalysts for overall water splitting, it only takes 1.64 V to deliver current density of 10 mA cm-2 and preserves remarkable long-term stability for at least 120 h for OER and HER applications. This work validates the promising properties of MXene incorporated PBA-derived materials for facilitating electrocatalytic OER and HER.

In Chapter 4, it’s demonstrated that as-proposed CoFe PBA/ MXene heterostructure can be used as a self-supporting substrate to derive ternary transition metal phosphides. The Ni additive will interaction with metal ions of CoFe PBA to establish trimetallic layered double hydroxides (LDHs) nanosheets protruding from CoFe PBA structures in the hydrothermal process, which can improve the contact ability with electrolyte and expedite electron and mass transport. By phosphorization, the hierarchical structure of trimetallic phosphide was obtained, which furnishes abundant active sites and enhances electrochemical performances toward OER and HER catalyzation. In this research, it’s further exemplified the importance of enhanced electrocatalytic efficiencies resulting from the decent architecture induced by adequate Ni contents and outstanding electrocatalytic properties of mixed metal phosphide. Benefiting from the structural and the compositional advantages, the as-synthesized trimetallic phosphide on MXene (P-0.4 Ni-CoFe/MXene) exhibits fascinating electrocatalytic efficiencies with low overpotentials of 219 mV and 92 mV toward OER and HER at 10 mA cm-2 in alkaline solution. For overall water splitting, it only takes the cell voltages of 1.55 V to reach current density of 10 mA cm-2 and keeps the catalytic activities with eminent long-term stabilities at least for 120 h for OER and HER applications. This work suggests that the electrocatalytic properties can be optimized with morphologically and compositionally engineered strategies, and the P-0.4 Ni-CoFe/MXene holds great feasibility to act as a bifunctional electrocatalyst for water splitting. Based on the core concept of Chapter 3 and Chapter 4, PBA nanocubes can in-situ grow on MXene to act as a precursor, followed by suitable annealing processes like phosphorization and sulfurization, metal composition strategy, or morphological design to derive manifold transitional metal-based composites as electrocatalysts. The pathway proposed in this thesis can offer a rational design concept to develop electrocatalysts with optimized catalytic activity in the field of energy application.