建構電催化水與二氧化碳還原之動態指標

Abstract

鑒於全球氣候變暖的嚴重問題，可再生能源需求急劇增加，電催化水與二氧化碳還原對此可以作為一個具有前景的方法去取代大規模化石燃料的使用。然而，由於固液界面的複雜性以及觸媒原子結構在反應當下的動態變化，我們一直無法深入了解反應機制，因此，我們以實驗的方法去研究調控催化功能的主要因素。首先，我們通過氫析反應（HER）研究中間體的結合特性與電化學指標（總表面電荷）的相關性，這個概念提供了一種可行的途徑，能用實驗方法研究中間體和電極表面結合特性，實現了由於複雜的固液界面和電催化劑在反應中的轉變，而在理論計算中受到限制的薩巴捷原則。我們發現在5 個動態d 電子下的中間體擁有最佳結合特性。其次，銅的氧化態在電催化領域被認為與產物分佈有高度相關性，然而對於調整催化功能而言，文獻中卻發現不一致的銅氧化態。為了澄清這一點，我們提出了一個(亞)表面氧指標（κ），用以了解這種不一致性。通過使用κ 進行(亞)表面價態的研究，我們獲得一個最佳的催化劑（Cu2O@Pd2.31），其在-0.83 V 時提供了0.33 A cm-2的多碳產物部份電流密度，並且其法拉第效率達到了83.5%。最後，我們提出了一個量化指標（ψ）來衡量廣泛應用於增強電催化性能的雙金屬電催化劑（CuxAuy）的原子分布情況。該指標闡明了在電催化過程中鄰近原子有序程度度和晶體性的動態變化，並有助於解釋結構對催化功能的影響，解決了文獻中觀察到的雙金屬觸媒效率不一致的未知性質。本論文旨在以實驗的方法揭示電催化的本質，加強實驗與理論的相關性，進一步能更理解反應機制，並有助於未來設計新型催化劑時，提供了新的見解。

In response to the dramatic global warming, it is of soaring demand for the renewable energy to replace the considerable consumption of fossil fuel, where the electrocatalysis paves a promising route. Yet, the fundamental insight into the reaction mechanisms has been elusive due to the complexity of the solid-liquid interface as well as the transformative atomic structure. Herein, we studied the factors that predominate the catalytic functionality. Firstly, we correlated the binding nature of the intermediate to the electrochemical descriptor, total surface charge, in hydrogen evolution reaction (HER). This concept provided a promising way to empirically investigate the binding nature of the intermediate, realizing Sabatier principle which has been limited in the theoretical calculation due to the complex solid-liquid interface and the transformative electrocatalyst. We revealed the optimized binding nature of the hydrogen intermediate at 5 of dynamic d electrons. Secondly, the Cu oxidation state has been reported to firmly correlate to the product profile whereas it has been found the inconsistent Cu oxidation state for the catalytic functionality in the literature. To clarify this, we proposed a descriptor of (sub)surface oxygen (κ) to untangle such inconsistency. Through the maneuver of κ, an optimum catalyst (Cu2O@Pd2.31) delivered the multi-carbon partial current density of 0.33 A cm-2 with a faradaic efficiency of 83.5 % at -0.83 V. Finally, we proposed a quantitative index (ψ) to scale the atomic distribution of bimetallicelectrocatalysts (CuxAuy), where such design strategy of the bimetallic catalyst has been widely employed to enhance the electrocatalytic performance. This index elucidated the order-of-neighbor degree and the crystallinity, which was dynamic during electrocatalysis and contributed to the catalytic functionality. The ψ explicated the unknown nature of the various atomic interactions that led to the discrepancy of the observed efficiency in literature. In sum, this dissertation aimed to experimentally unveil the nature of electrocatalysis and improve correlation to the theory, further providing insight for understanding mechanism and help the community design novel catalysts in the future.