Porous PVA skin-covered thin Zirfon-type separator as a new approach boosting high-rate alkaline water electrolysis beyond 1000 hours’ lifespan

Abstract

Regulating the pore structure of a zirfon-based diaphragm is critical to promoting a high-rate alkaline electrolyzer, but it is still a big challenge to respond “trade-off” between the thickness of the diaphragm and the current density/gas barrier behavior. In this work, a porous hydrophilic skin layer with ∼μm thick of polyvinyl alcohol (PVA) has been successfully constructed and casted onto the thin zirfon-type separator composite (V-Zirfon-350 ​μm). The V-Zirfon-350 ​μm separator generates a high KOH uptake (> 90%), low area resistance (0.2026 ​Ω ​cm2) but a low electrolyte permeation flux density (5.2 × 10−4 mL ​cm−2 ​s−1 ​at 0.5 ​bar), which largely surpasses the state-of-the-art commercial Zirfon UTP-500 ​μm diaphragm. When coupled with Raney Ni cathode and NiCoMo-LDH anode catalysts, the V-Zirfon-350 ​μm separator offers a high current density over 1300 ​mA ​cm−2 @2.0 ​V (80 ​°C in 30% KOH) and a superior stability of 300 ​h under 800 ​mA ​cm−2 for alkaline water electrolysis (AWE). Specifically, the voltage is merely ∼3.5 ​V for two electrolytic cells connected in series, which can be even conducted for more than 1300 ​h at different operational conditions. This work provides a novel methodology for the practical application of a thin Zirfon-based diaphragm.

Keywords

• Alkaline water electrolysis
• Porous separator
• Zirfon type
• Polyvinyl alcohol
• Skin layer