High-Temperature Water Electrolysis Properties of Membrane Electrode Assemblies with Nafion and Crosslinked Sulfonated Polyphenylsulfone Membranes by Using a Decal Method.

To improve the stability of high-temperature water electrolysis, I prepared membrane electrode assemblies (MEAs) using a decal method and investigated their water electrolysis properties. Nafion 115 and crosslinked sulfonated polyphenylsulfone (CSPPSU) membranes were used. IrO was used as the oxygen evolution reaction (OER) catalyst, and Pt/C was used as the hydrogen evolution reaction (HER) catalyst. The conductivity of the CSPPSU membrane at 80 °C and 90% RH (relative humidity) is about four times lower than that of the Nafion 115 membrane. Single-cell water electrolysis was performed while measuring the current density and performing electrochemical impedance spectroscopy (EIS) at cell temperatures from 80 to 150 °C and the stability of the current density over time at 120 °C and 1.7 V. The current density of water electrolysis using Nafion 115 and CSPPSU membranes at 150 °C and 2 V was 1.2 A/cm for both. The current density of the water electrolysis using the CSPPSU membrane at 120 °C and 1.7 V was stable for 40 h. The decal method improved the contact between the CSPPSU membrane and the catalyst electrode, and a stable current density was obtained.