2.3 Pretreatment of the substrate
The purchased microporous stainless steel substrate was polished to smooth the surface and then ultrasonically cleaned three times with a commercial cleaning agent, absolute ethanol, and deionized water for 0.5 h, respectively. The impurities on the stainless steel surface were washed off and the substrate was dried for subsequent use. An appropriate amount of multi-walled CNTs was weighed and poured into 1 L deionized water with ultrasonic treatment for 60 min to prepare a solution of CNTs with uniform density for use. The tubular porous stainless steel (SS) was then cut with appropriate length and immersed in the as-prepared CNTs solution, followed by vacuum filtration to modify the outer wall of the stainless steel to decrease the pore size with good electrical conductivity for subsequent electrophoretic deposition. We would wipe the CNTs on the tube surface to better fill the substrate’s pores and large holes. The surface flatness was further improved, which is beneficial to reduce membrane defects in the subsequent nanosheet assembly process.