Advanced electrode structuring and catalyst layer arrangement for high-performance brine electrolyzers producing HCl and NaOH

Abstract

This study explored methods to optimize the composition and structure of the electrodes for three-compartment brine electrolyzers that can simultaneously produce sodium hydroxide (NaOH) and hydrochloric acid (HCl) from concentrated brine. High-performance electrodes were developed using a substrate made of a flexible carbon cloth instead of hard metal meshes. It is found that incorporating an optimized dense carbon layer into the carbon cloth-based cathode boosts electrolyzer performance by 110 %. It also outperforms Ni-mesh based electrodes. The most crucial finding is that the electrolyzer’s performance is significantly affected by the location of the catalyst layer at the cathode. Additional gains of 12 % in both the reaction rate and caustic efficiency are achieved by strategically placing the catalyst layer on the flow field side, away from the membrane. Ion permeability experiments further elucidate the relationship between catalyst layer location and electrolyzer performance. The permeation rate of H+ is much faster than that of OH？, and therefore, by positioning the catalyst layer on the flow field side, the recombination rate of the two ions is retarded, leading to a significant increase in electrolyzer performance. This study successfully modifies flexible carbon cloth-based electrodes and optimizes the catalyst layer location at the cathode to develop practical, advanced brine electrolyzers.