Understanding Surface Behavior for Propylene Epoxidation on Pd-Based Gas Diffusion Electrode = 팔라듐 기반 기체 확산 전극에서 프로필렌 에폭시화 반응의 표면 특성 및 거동 분석

다국어 초록 (Multilingual Abstract)

Electrochemical anodic oxidation of organic molecules in water electrolysis processes is gaining attention as a promising strategy to replace the conventional oxygen evolution reaction (OER). This approach offers the advantage of not only reducing the cell voltage required for electrolysis but also simultaneously producing value-added compounds. Among various substrates, propylene is particularly attractive as it can be electrochemically converted to propylene oxide (PO), an industrially important intermediate. However, studying the propylene oxidation reaction in aqueous electrolytes faces significant constraints: propylene's low water solubility and strong competition with the OER in the anodic potential region. Consequently, the performance observed in conventional liquid-phase electrochemical cells is often dominated by mass transport limitations and interfacial effects rather than the intrinsic activity of the catalyst.

This dissertation investigates the propylene oxidation reaction on a Pd/C electrode using a custom-designed gas diffusion electrode (GDE) system. The GDE configuration enhances propylene supply to the reaction interface and enables stable formation of the gas–liquid–solid triple phase boundary (TPB). To elucidate the influence of interfacial wettability, plasma treatment was applied to the microporous layer (MPL), and the Nafion content within the catalyst layer was minimized and precisely controlled. Furthermore, electrochemical measurements conducted under propylene feed conditions were combined with quantitative ¹H NMR analysis to identify and quantify liquid-phase oxidation products, specifically evaluating the formation behavior of PO and propylene glycol (PG).

Experimental results showed that the product distribution was highly sensitive to the applied potential and the local interfacial environment. At relatively low anodic potentials (1.75 V vs RHE), liquid-phase product formation was limited. However, at higher potentials (1.95 V vs RHE), the Faraday efficiencies of PO and PG increased, while the contribution of the parasitic OER reaction also intensified. These results suggest that product selectivity is determined by the interaction of external factors such as the Pd surface state, competitive anodic reaction pathways, and propylene transfer and TPB wettability. This study provides useful insights for designing GDE-based electrodes and establishing operating conditions for anodic olefin oxidation, laying the groundwork for developing electrolytic systems that combine hydrogen production with the synthesis of high-value-added chemicals.

목차 (Table of Contents)

• 1. Introduction 1
• 1.1 Water electrolysis 1
• 1.2 electrocatalysis 1
• 1.3 Electrochemistry for value added chemical materials 4
• 2. Palladium on carbon as Catalysts for electrochemical Propylene Oxidation 7
• 2.1 Chemical and Materials 7
• 2.2 Synthesis of Pd/C 7
• 2.3 Gas diffusion electrode (GDE) setup 7
• 2.4 Characterization 8
• 2.5 Electrochemical measurements 8
• 2.6 Product analysis 9
• 2.7 Results and Discussion 10
• 3. Conclusion 23
• 4. Reference 24