Modified dip-coating method for fabrication of pinhole-free supports for hydrogen-separation silica membranes

Myagmarjav, O.  ; Noguchi, Hiroki  ; Tanaka, Nobuyuki ; Kamiji, Yu; Ono, Masato ; Takegami, Hiroaki ; Nomura, Mikihiro*; Kubo, Shinji  

Clean and alternative energy are driving global research for sustainability, with a focus on hydrogen production through the innovative thermochemical water-splitting iodine-sulfur (IS) process. This process, powered by solar or nuclear energy, decomposes water into hydrogen, relying on three chemical reactions (Bunsen reaction, sulfuric acid decomposition and hydrogen iodide decomposition. A major challenge is efficiently separating hydrogen from iodine and hydrogen iodide generated during HI decomposition (2HI H + I). Silica membranes offer a promising solution due to their thermal and chemical stability. These membranes are produced as thin silica films carefully coated onto porous supports. However, it is crucial to note that the presence of pinhole defects in these supports can result in an undesirable deterioration, and even the loss of the typical separation capabilities of silica membranes. To address the issue of pinhole defects in the membrane support, a modified dip-coating technique was introduced. This innovative approach utilized rotational dipping, resulting in a new support composed of two distinct layers of -AlO with a gradient structure that demonstrated outstanding pinhole prevention, reproducibility, and a consistently smooth surface. These improvements were achieved through careful consideration of factors such as rotary speed, duration, and coating solution properties.