Thin Diaphragms with High Selectivity for Alkaline Water Eelectrolysis Application

Alkaline water electrolysis (AWE) is well-suited for the mass production of hydrogen from renewable energy sources due to its low installation cost, which results from the absence of precious metal catalysts. However, AWE poses a risk of hydrogen permeation through the diaphragm at low loads, which can increase the concentration of hydrogen in oxygen and potentially lead to fire or explosion. Therefore, a diaphragm with strong gas barrier properties is needed. Additionally, due to the low efficiency of AWE, there is a need for a diaphragm that provides low area resistance [1].<br/>In this study, we developed a thin-film diaphragm that simultaneously exhibits low membrane resistance and reduced gas permeability. To achieve this, we introduced a polymeric additive, which is expected to increase the porosity and strengthen the connection between zirconia(ZrO₂)nanoparticles and the polymer matrix as a binder. The diaphragm was fabricated by dispersing the polymeric additive and polysulfone (PSf) with ZrO₂ in N-Methyl-2-Pyrrolidone (NMP) using a planetary mixer to make a slurry. This slurry was then coated on both sides of a polyphenylenesulfide (PPS) support using a roll-to-roll process. Then, the porous structure was formed using the non-solvent induced phase separation (NIPS) method in a water bath. The diaphragm with polymeric additive (A/PSU-10) exhibited a 14% higher bubble point (5.48 bar), lower hydrogen permeability (less than 5 × 10^-12 mol s^-1 bar^-1), lower area resistance (less than 0.10 Ω cm²), and 24% higher AWE unit cell performance at 1.80V (1.65 A cm^-2) compared to the diaphragm using only PSf (A/PSU-0).<br/>To further enhance the gas permeation barrier of the diaphragm, a hydrophilic skin layer based on crosslinked polyvinyl alcohol (PVA) was coated onto the diaphragm, a process was previously developed and reported by our research team [2]. An aqueous PVA solution was air-sprayed onto the surface of the diaphragm, and the resulting PVA layer was crosslinked using glutaraldehyde. The diaphragm with optimized composition and crosslinked PVA skin layer (cA/PSU-10) exhibited a 252% higher bubble point (7.61 bar), lower hydrogen permeability (less than 1 × 10^-12 mol s^-1 bar^-1), lower area resistance (less than 0.15 Ω cm²), and 101% higher AWE unit cell performance at 1.80V (1.49 A cm^-2) compared to the commercial diaphragm (Zirfon UTP 500).<br/><br/>References<br/>[1] Yu, Jinghua, et al. "Hydrophilic Chitosan-Doped Composite Diaphragm Reducing Gas Permeation for Alkaline Water Electrolysis Producing Hydrogen." <i>ACS Applied Materials & Interfaces</i> 16.1 (2023): 1394-1403.<br/>[2] Kim, Sohee, et al. "Highly selective porous separator with thin skin layer for alkaline water electrolysis." <i>Journal of Power Sources</i> 524 (2022): 231059.