低壓電漿改質鎳鐵雙金屬析氧反應之電催化劑

Abstract

本研究將鎳鐵雙金屬有機框架(Metal Organic Frameworks, MOF)以水熱合成法(hydrothermal synthesis)原位生長在在鎳泡沫上，接著使用低壓電漿清潔機(plasma cleaner)，以Ar、Ar/H2(95:5)和Ar/O2(95:5)作為工作氣體進行電漿後處理，探索不同電漿氣體對鎳鐵雙金屬有機框架進行表面改質在析氧反應(oxygen evolution reaction, OER)各方面性能表現的影響。由此開發的電催化劑在鹼性溶液(1 M KOH)中進行測試。結果表明，以Ar/H2(95:5)還原性氣體電漿處理明顯提高了RuCo/ANF的電催化活性，實現在電流密度10 mA/cm2下149 mV的過電位，這可能是由於氫自由基的摻入使得表面的氧化物被還原。接著利用電化學阻抗圖譜(EIS)和循環伏安法(CV)分析進行電化學量測，顯示出電荷轉移阻抗顯著降低以及電雙層電容明顯提升，分別證明電荷轉移加速和電化學表面積擴大。最後經由12小時的連續循環測試以評估所製備的電催化劑之耐久性，觀察到循環後經由摻氫電漿處理的電極過電位僅增加29 mV。此現象乃歸因於反應產生的氣泡會衝擊電極，導致電極材料本身劣化，但仍保持令人滿意的過電位可能是由於基材和MOF之間穩定的機械粘附，使活性位點得到充分利用。

In this study, nickel-iron bimetallic organic frameworks were grown in-situ on nickel foam by the hydrothermal method. Then, Ar, Ar/H2(95:5) and Ar/O2(95:5) were used as working gases for plasma post-treatment to explore the effects of different plasma gases on the surface modification of nickel-iron bimetallic organic frameworks in all aspects of OER performance. The developed electrocatalysts perform oxygen evolution reaction in alkaline solution (1 M KOH) showing that plasma treatment with Ar/H2(95:5) gas significantly improved the electrocatalytic activity of NiFe-MOFs/NF, achieving an overpotential of 149 mV at a current density of 10 mA/cm2, attributing to the reduction of surface oxides due to the incorporation of hydrogen radicals. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) analysis showed that a great reduction in charge transfer impedance and a significant increase in electric double layer capacitance, proving the acceleration of charge transfer and the expansion of electrochemical surface area, respectively. Finally, the durability of the prepared electrocatalyst was evaluated by 12 h continuous cycle test. The overpotential of the electrode treated with hydrogen-containing plasma only increased by 29 mV after cycling. This phenomenon is attributed to bubbles generated by the reaction impacting the electrode, causing the electrode material to deteriorate itself. The satisfactory overpotential may be due to the stable mechanical adhesion between the substrate and the MOF, making the active sites be fully utilized.