介金屬化合物對合成奈米多孔結構的影響—探討銅鋁合金的θ與η相

Abstract

奈米多孔銅有著密度低、質量輕、高表面積、等優點，又擁有良好的導電性、導熱性以及電化學穩定性，可運用於感測、催化劑、鋰電池、表面增強拉曼散射、超級電容、二氧化碳還原等等領域，是前景可期的一項新興材料。本研究旨在探討不同介金屬化合物對合成奈米多孔結構的影響，本研究以銅鋁合金中的θ與η相為例以進行討論，將不同合金相的銅鋁合金透過不同電解液以及溫度的搭配進行選擇性腐蝕以合成在微結構上各有差異的奈米多孔銅，並以二氧化碳還原反應作為應用上的測試。 首先利用真空電弧熔煉法製作四種組成比例的銅鋁前置合金(precursor alloy)：Cu18Al82、Cu30Al70、Cu33Al67以及Cu37Al63。此四種合金各自含有不同比例的固溶相(α相)及介金屬化合物(θ相與η相)，因此造就了不同的微結構。接著使用不同種類的電解液以及不同的環境溫度對前置合金進行自由腐蝕驅動去合金化，利用元素間還原電位的不同將活性較高的鋁成分選擇性去除，留下活性較低的銅並重組成奈米孔洞結構 (Nanoporous Cu)。藉由掃描式電子顯微鏡與能量散射光譜儀的觀察，確認在銅鋁合金產生奈米孔洞結構的情況。 本研究成功的在銅鋁合金的介金屬化合物相上合成出支架大小分布在29nm~174nm之間的奈米多孔銅結構。在不同形式的θ相同時存在時，奈米孔洞結構並不存在明顯差異。另外，在酸與鹼的電解液中，η相上的反應有所差異，於鹼中無法完全的去合金化。對於二氧化碳還原反應，目前結果顯示，支架越小的材還原效果越好，並且共晶結構所產生的微米-奈米多層次結構，有助於提升還原效果。

In this study, nanoporous copper with ligament sizes ranging from 29 to 174 nm was successfully synthesized by dealloying Cu18Al82, Cu30Al70, Cu33Al67, and Cu37Al63 alloys. The purpose of this study is to investigate the effect of the intermetallic compound on the synthesis of nanoporous structure, and the θ and η phases of copper-aluminum alloy are focused. Nanoporous copper has the advantages of light in weight, high surface area, good electrical and thermal conductivity, and wonderful electrochemical stability. It can be applied in sensing, catalyst, lithium battery, surface-enhanced Raman scattering, and carbon dioxide reduction, which is being more and more important nowadays. Firstly, four kinds of compositional copper-aluminum precursor alloys were fabricated by vacuum arc melting: Cu18Al82, Cu30Al70, Cu33Al67, and Cu37Al63. Each of the four alloys contains different ratios of solid solution phase (α phase) and intermetallic compound (θ phase and η phase), thus creating a different microstructure. Then, the precursor is dealloyed using different kinds of electrolytes and under different temperatures. Aluminum, which is the more electrochemically active element of the two in the precursor alloy, is selectively removed to form nanoporous copper structures (Nanoporous Cu). The effect of concentrations of electrolyte on the resultant nanoporous structure was also evaluated by the use of Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometer (EDS). The result shows that when two different kinds of θ phase exist at the same time, there is no significant difference between the two. Besides, the η phase can be completely dealloyed in acid but not in alkali. For the carbon dioxide reduction reaction, the current results show that the smaller the ligament of the nanoporous copper, the better the effect of the CO2 reduction, and the micro-nano multi-layer structure produced by the eutectic phase contributes to the improvement of the reduction effect.