Electrodes and Diaphragms for Alkaline Water Electrolysis above 130°C

Alkaline water electrolysis (AWE) is the leading technology for the production of green hydrogen. It relies heavily on alkali-resistant core components such as bipolar plates, current collectors, sealings, electrodes incl. electrocatalysts, and diaphragms. The latter is primarily based on polyphenylene sulfide (PPS). Zirfon© from Agfa-Gevaert NV, a recognized product, includes additional inorganic fillers. A significant challenge for Zirfon-type diaphragms is the exposure to temperatures (e.g., operation temperatures or hot spots) exceeding the decomposition temperature, typically between 100 °C and 130 °C under AWE conditions. A temperature-stable diaphragm could reduce degradation and - maybe more important - enhance the water electrolysis efficiency. In the industry-lead project AWEC++, Fraunhofer IKTS and partners are developing components and a stack that enables operation temperatures above 130 °C (above 25 bar). The consortium has the capability to manufacture electrodes, the diaphragm, bipolar plates as well as the stack and a demonstration electrolyzer (20 kW). The key component is a scalable, fully inorganic diaphragm which is produced starting from inorganic meshes. It is (i) stable in aqueous 35 % KOH solution at 200 °C and 35 bar for at least 7 days, (ii) has an average pore diameter of 300 nm (as determined via bubble point analysis), and (iii) exhibits in aqueous 35 % KOH an area specific resistance (ASR) of 1.4 Ω cm2 (thickness: 450 μm). In this project phase IKTS will complete a 5-level short stack with an active area of 100 cm2 with a PGM-free current density of 500 mA cm‑2 at 2.1 V.