鈀銅雙金屬奈米結構應用於電催化二氧化碳還原產物之研究

Abstract

在全球暖化的議題延燒下，傳統以石油燃料為主要產能來源勢必需要減少用量，科學家們開始研究替代性能源，此外，也有研究是針對將二氧化碳轉成其他化合物，再繼續燃燒供能使用，形成一個環保的系統。 二氧化碳還原因此備受重視，而二氧化碳面臨的兩個大問題為：(1)產物選擇性低 (2)過電壓大，因此研究主要針對改善這兩個問題。 Hori教授大致上將用來電催化二氧化碳還原反應的金屬分成四類，其中，銅因為具有產碳氫化合物特性而開始被大量研究，不論是銅金屬、奈米銅，或是不同形貌、晶面、氧化價數的銅，發現銅在奈米粒子下形貌以及表面粗糙度對於還原產物具有一定的影響。又有研究發現不單是銅金屬，非銅金屬組合如鈀金合金可以產多碳產物，其藉由調控催化劑表面與一氧化碳的鍵結能力控制產物，結合與一氧化碳鍵結強的鈀與弱的金，造成此效果，由此可見，雙金屬具有協同效應，也因為兩金屬造成催化劑的特殊性質。 本研究結合鈀與銅作為雙金屬材料，藉由調控銅的濃度合成出不同形貌的鈀-銅雙金屬奈米材料，包含有單分子氧化銅分佈於鈀奈米立方、銅金屬簇於鈀奈米立方以及銅-鈀核殼結構，發現其中在低濃度銅的樣品具有對乙醇的高選擇性，在-0.7V(vs. RHE)達到48.86%的高產率。經由臨場x光吸收圖譜推測進行二氧化碳還原反應的活性位置應該位於單顆氧化銅上，且Pd89Cu11有最高乙醇產率的原因為其鈀表面上的單顆氧化銅的分佈最為適當，促成還原出乙醇的最佳條件。

As the issue of global warming is hot in the world, scientists are focused on the green energy and CO2 reduction reaction to cut down on the use of fossil fuel and turn CO2 into good use. The two main problems for CO2 reduction reaction are (1) low selectivity for products (2) high overpotential. As a result, many research discussed these problems and tried to dissolve the problems. Professor Hori has classified metal that can catalyze CO2 reduction reaction into four groups. Among them, Cu is the only metal that can produce hydrocarbons, which is high energy products. However, in recent years, there's research about combining two different metal so that the catalyst display different reaction, which can even produce products that every single metal can’t produce. The classical case is bimetal of palladium and gold, both of which are not Cu. But with them combining, they produce multi hydrocarbon products. The reason is that they have different binding energy to CO. To have the same effect for that, we synthesize bimetal catalyst of Palladium and Copper. We found that in the low concentration of Cu, the catalyst has high ethanol faradic efficiency about 48.86％.