Atomic layer deposition enabled hydrophilic treatment of PTFE separators for intermediate temperature alkaline water electrolysis

• ALD of ZrO 2 on PTFE enables stable separators for intermediate temperature alkaline water electrolysis. • Optimized ALD process improves hydrophilicity and electrolyte filling of PTFE. • Aspect ratio introduced as a design metric for pore-scale coating conformality. • Modified PTFE membranes show thermal stability up to ∼ 130 °C for 1000 h. • Comparative analysis with commercial separators confirms industrial relevance. Alkaline water electrolysis is gaining traction for large-scale green hydrogen production due to its cost-effectiveness and scalability. Operating alkaline electrolysis at intermediate temperatures of 100–200 °C can enhance reaction kinetics and reduce energy losses, but this requires separators with improved thermal, mechanical, and chemical stability. Traditional separators like Zirfon UTP 500 are limited to below 110 °C due to degradation and mechanical shortcomings. This study explores the use of microporous polytetrafluoroethylene as a separator substrate, modified through atomic layer deposition (ALD) of zirconium dioxide. This modification aims to minimize its hydrophobicity while maintaining chemical stability. We optimized ALD parameters, including deposition temperature and oxygen source choice. Ozone pretreatment to activate the substrate surface before deposition was notably effective, enhancing adherence of the oxide layer. The aspect ratio of the PTFE substrate proved critical for improving coating penetration. Electrochemical tests showed that PTFE membranes with an aspect ratio of 24, treated with 300 ALD cycles at 100 °C using ozone and water, exhibited an ohmic area-specific resistance of 0.38 Ω·cm 2 at 60 °C in 31 wt% KOH solution, approaching the conductivity of the benchmark Zirfon UTP-500. Long-term chemical stability tests conducted in an autoclave at 130 °C in 40 wt% KOH confirmed the membrane’s durability over 1000 h, with minimal degradation. This work indicates that ALD-functionalized PTFE is a promising option for stable and efficient separators in intermediate-temperature alkaline water electrolysis.