利用實驗與計算研究探討氫氣氧化在固態氧化物燃料電池上金屬陽極的反應趨勢

Abstract

本篇論文藉由實驗方法與電腦計算來探討固態氧化物燃料電池陽極上的氫氣氧化反應在過渡金屬Co、Ni、Cu (第三週期) Rh、Pd、Ag (第四週期) 和 Ir、Pt、Au (第五週期)的趨勢。在實驗部分我們將Co/YSZ、Ni/YSZ、Cu/YSZ、 Rh/YSZ、Pd/YSZ、Ag/YSZ、Ir/YSZ、Pt/YSZ、Au/YSZ的陽極材料，條理式利用屏幕塗佈法來製作電解質支撐電池。而組裝後的電池 使用XRD、SEM、EDS來對陽極分別進行化合物組成、表面微結構、確認元素組成的特性分析，並且通入氫氣做為燃料且使用電位儀及阻抗分析儀測試電池在600-800 oC的電化學特性。而實驗的結果發現Au、Ag作為陽極材料的電池有最好的效果。在計算部分中我們透過O* + H*  OH* 及 OH* + H*  H2O*兩個路徑在純金屬、ZrO2、金屬吸附的ZrO2三個部份的反應計算，去模擬氫氣氧化在電極、YSZ電解質及金屬/電解質介面上的反應機制。在計算的結果，反應在Au、Ag、Cu的金屬/電解質介面上有最小的反應活化能，這也是因為分子在這表面上的吸附能相較其他來的低。由此發現電池陽極的反應效果的好壞跟跟陽極表面的分子吸附強弱有關係。The anodic reaction for hydrogen fuel (hydrogen oxidation reaction, HOR) for solid oxide fuel cell (SOFC) system has been experimentally and computationally investigated on the 3d (Co, Ni, Cu), 4d (Rh, Pd, Ag) and 5d (Ir, Pt, Au) transition metals. Experimentally, the electrolyte-supported SOFCs with anodes of Co/YSZ, Ni/YSZ, Cu/YSZ, Pd/YSZ, Ag/YSZ, Ir/YSZ, Pt/YSZ and Au/YSZ have been systematically fabricated by screen printing method. The fabricated fuel cells have been initially characterized from XRD, SEM and EDX to examine their chemical compositions and microstructures. The electrocatalytic performance for HOR has been further determined by Potentiostat and electrochemical impedance spectroscopy (EIS) at 600 – 800 oC. The experimental result shows that Ag and Au-based anode have better performance. Computationally, we thoroughly examine the two elementary steps: O* + H*  OH* and OH* + H*  H2O*, on pure metals, ZrO2 surfaces and metal adatom modified ZrO2 surfaces to simulate HOR on electrode (2PB), YSZ electrolyte (2PB) and metal/electrolyte (3PB) surfaces, respectively. The computational results shows relatively lower reaction barriers on Ag and Au-based surfaces, attributable to the lower adsorption energies of H*, O* and OH* on these surfaces. On the other hand, the better HOR performance observed in SOFC experiment correspond to the weaker binding energy between anode surfaces and adspices.