High chemical stability poly(oxindole biphenylene)/ZrO2 porous separator for alkaline water electrolysis

Porous separators are essential for alkaline electrochemical energy technologies, such as alkaline water electrolyzers (AWEs). These separators are promising alternatives to dense membranes because they offer the potential for low cost and high ionic conductivity. However, two significant challenges in developing efficient and durable alkaline energy systems are the suppression of hydroxide ions-induced degradation and the reduction of gas permeation in porous separators. Compared to hydrophobic polysulfone (PSF), KOH-doped poly (oxindole biphenylene) (POBP) is a highly stable ion-solvating polymer that can conduct both potassium and hydroxide ions. Building upon this, a series of porous separators based on POBP polymer with different zirconia loads were designed using NIPS to investigate the chemical stability and water electrolysis performance where the Z60 separator exhibits remarkable characteristics, including low area resistance (0.227 Ω cm2), high bubble point pressure (0.813 MPa), low H2 permeability (0.5 L min−1·cm−2) and exceptional 5040 h of ex-situ durability in 6 M KOH at 80 °C. Furthermore, the Z60 diaphragm showed a higher breaking time and lower weight loss after 261 h at 80 °C in the Fenton reagent, with the remaining mass being Z60 was 38 %. Notably, the Z60 diaphragm, when equipped with Ni–Al catalysts, achieved a current density of 0.5 A/cm2 at 1.7 V, which surpasses that of Zirfon (0.5 A/cm2 at 1.8 V). More importantly, when using Ni foam catalysts, the Z60 diaphragm demonstrated stable operation under 0.125 and 0.5 A/cm2 current densities at 80 °C for more than 900 h and 1200 h, significantly improving the durability of the porous separators. The results of this study showed that the blending of POBP can lead to the development of highly chemically stable porous diaphragms, thereby opening up a new avenue for advanced AWEs.