製備鈀合金膜和金屬陶瓷複合膜應用於氫氣分離

Abstract

本研究利用逐步無電鍍法沉積鈀合金薄膜於多孔氧化鋁管上，並在高溫環境下作H2和CO2分離。由於基材表面粗糙度太大，藉由塗佈氧化鋁緩衝層平坦化表面；另外，不同之氧化鋁相結構會影響敏化、活化之結果，發現以γ-Al2O3存在有利於後續無電鍍製程；在無電鍍過程中除了銅有均勻性成核問題外，其它金屬膜巨觀上都有均勻覆蓋；氣體分離測試部份，薄膜對於H2和CO2之分離率和透氫率都不高，推測原因是薄膜漏氣量太多。 另外，本研究還製備出一金屬陶瓷複合材料，結合具有導氫原子能力之金屬(Pd)和質導陶瓷(BaCe0.4Zr0.4Gd0.1Dy0.1O3-x; BCZGD)。陶瓷是經由燃燒法合成，而金屬陶瓷複合膜是混合相同體積之粉末壓錠成型，最後在1450°C空氣下燒結15小時。材料性質透過SEM、EDS、XRD、TGA鑑定分析；EDS顯示無論在材料表面或是斷面都可看出鈀金屬均勻分佈在陶瓷相中；XRD顯示除了金屬與陶瓷之特徵峰外，試片燒結前後並無其它明顯之雜相生成；TGA也證實了材料對CO2有不錯之化學穩定性；氣體測試部份，氣體流量透過氣相層析儀量測與分析，同時也探討不同溫度與氫分壓對氫流量之影響；試片在室溫下氦氣漏氣只有0.01 mol%且H2和CO2已經可以有效分離。

We fabricate a Pd-based alloy membrane on a porous alumina tube via a sequential electroless deposition technique. The membrane enables the separation of hydrogen from a mixture of hydrogen and carbon dioxide at elevated temperature. A buffer layer is adopted to reduce the surface roughness. The calcination temperature causes the alumina to form different phases, among which the γ-Al2O3 is suitable for the electroless deposition process. During the electroless deposition process, all the metals except copper are homogeneously formed. The permeability of H2 and the selectivity of H2/CO2 are very low because of the intrinsic leakage. We also fabricate a cermet composite membrane composed of a hydrogen transporting metal (Pd) and a proton-conducting ceramic (BaCe0.4Zr0.4Gd0.1Dy0.1O3-x, BCZGD). The BCZGD proton-conducting perovskite powders are synthesized via a combustion method. The Pd-BCZGD cermet membrane is then fabricated by pressing a mixture of the Pd and BCZGD powders at equal volume, followed by sintering at 1450°C for 15 h in air. The properties of the Pd-BCZGD membrane are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal gravimetric analysis (TGA). The element map on the membrane surface and cross-section demonstrate that the Pd is uniformly-distributed in the perovskite phase. The XRD indicates characteristic peaks to metallic Pd and BCZGD perovskite phases. TGA confirms that the cermet membrane is chemically stable against CO2. Lastly, the flux from a gas chromatography (GC) are determined as a function of temperature and under different feed gas hydrogen pressures. The leakage rate of He through the cermet membrane is only 0.01 mol% so the separation ratio of H2 and CO2 is large.