Significant improvement of both hydrogen permeation and catalytic activity of nickel hollow fiber membrane reactor by surface electrochemical modification

We developed a novel approach to modify the nickel hollow fiber membrane (NHFM) for enhanced H2 permeation and catalytic activity. In this work, the outer dense layer of the manufactured NHFM was precisely removed by surface electrochemical modification. A porous structure was formed on the membrane surface after the removal of the outer dense layer, but the inner dense layer still maintained intact. Compared to the raw membrane, not only H2 permeation of the modified membrane increased by approximately 2 times in the separation test, but also the catalytic activity of the modified membrane increased by 5 ∼ 7 times in the methane steam reforming (MSR) reaction test. Acid etching, electrochemical etching with various electrolyte solutions was comparably investigated for the removal of the outer dense layer. Acid etching showed low effectiveness and uneven surface modification as the etching process starts from the grain boundary. Electrochemical etching showed higher efficiency to achieve a uniform modification in a shorter etching time. Among the three investigated electrolytes, namely H2SO4, HCl and HNO3, H2SO4 had the best performance due to its complete remove of the outer dense layer and the formation of a uniform open porous structure on the membrane surface. The removal of the outer dense layer reduces mass transfer resistance for hydrogen permeation and allowed the formation of open porous structure to increase the specific surface area for more reaction catalytic sites. It is a highly efficient technique to improve both hydrogen permeation and catalytic activity for NHFM reactors.