Fabrication of Hydrogen-separating Composite Membranes for Separation-integrated Reaction Processes and Their Hydrogen Permeation Behavior

采用发展起来的超临界电镀技术，在孔径为0.06 μm的多孔Al_2O_3板载体上制备无缺陷的Pd-Ag合金膜，以抑制H_2的脆化，提高H_2的渗透率。采用由PdCl_2 （0.1 mol L^1）、AgNO_3 （0.005 mol L_1）、KBr （4.0 mol L_1）、KNO_2 （0.2 mol L_4）、H_3BO_3 （0.49 mol L_1）、C_2H_5NO_2 （0.1 mol L_1）和合适的表面活性剂组成的镀液，在超临界CO_2共存的条件下，在12 MPa下制备了一层薄而无缺陷的Pd-Ag合金膜。所得膜的平均厚度为2.2 μm，银含量为20 wt%。在673 K时H2的渗透系数为3.0 × 10^(-9) mol m^(-1) s^(-1) Pa^(-0.5)，大于纯钯膜。设计了一种新型的外循环超临界CO_2与镀液混合的电镀反应器，用于圆柱形支架。制备的膜完全无缺陷，合金成分Pd为77%，Ag为23%，膜厚为1.5 μm。但与平面支撑的复合膜相比，H_2渗透系数有所降低。这可能与支架孔隙中H_2渗透阻力增大有关。在723 K时，Ru的加入使钯银合金膜的H_2导电性提高了1.2倍。此外，超临界电镀技术也被应用于Pd化学镀，这需要在酸性条件下进行。一种化学镀液包括膦酸、膦酸盐和三甲胺硼烷作为还原剂。实验证实，超临界CO_2的共存抑制了FI2脆性裂纹的产生。

The fabrication of a defect-free Pd-Ag alloy membrane using a porous Al_2O_3 plate support (pore size, 0.06 μm) was tried using developed supercritical electroplating technique for the purpose of the suppression of H_2 embrittlement as well as the improvement of H_2 permeance. A thin and defect-free Pd-Ag alloy film was formed using a plating bath consisting of PdCl_2 (0.1 mol L^1), AgNO_3 (0.005 mol L_1), KBr (4.0 mol L_1), KNO_2 (0.2 mol L_4), H_3BO_3 (0.49 mol L_1), C_2H_5NO_2 (0.1 mol L_1), and a suitable surfactant at 12 MPa with the coexistence of supercritical CO_2. The average thickness and Ag content of the resulting membrane were 2.2 μm and 20 wt%, respectively. The H2 permeation coefficient at 673 K was 3.0 x 10^(-9) mol m^(-1) s^(-1) Pa^(-0.5), which was larger than the reported value of a pure palladium film.A new electroplating reactor with the outside circulation of the mixture of supercritical CO_2 and plating solution was designed for the application to a cylindrical support. The resulting membrane was completely defect-free and had the desirable alloy composition of Pd 77 wt% and Ag 23 wt%, and the thickness of 1.5 μm. Unfortunately, the H_2 permeation coefficient was decreased compared with that of the composite membrane using the planar support. It may be related to the increased resistance of H_2 permeation in the pores of the support. The addition of Ru to the Pd-Ag alloy film gave about 1.2 times higher H_2 permeance at 723 K.Additionally, the supercritical plating technique was also applied to Pd electroless plating, which should be conducted under acidic condition. A developed electroless plating bath includes phosphinic acid, phosphonate, and trimethylamine borane as the reducing agent. It was experimentally confirmed that the generation of cracks due to the FI2 embrittlement was suppressed by the coexistence of supercritical CO_2.