Water Electrolysis Using a Porous IrO₂/Ti/IrO₂ Catalyst Electrode and Nafion Membranes at Elevated Temperatures

Porous IrO₂/Ti/IrO₂ catalyst electrodes were obtained by coating IrO₂ on both sides of three types of porous Ti powder sheets (sample 1, sample 2, and sample 3) using different surface treatment methods, and a hydrogen evolution catalyst electrode was obtained by coating Pt/C on carbon gas diffusion layers. A Nafion115 membrane was used as an electrolyte for the membrane electrode assemblies (MEA). Water electrolysis was investigated at cell temperatures up to 150 °C, and the electrical characteristics of the three types of porous IrO₂/Ti/IrO₂ catalyst electrodes were investigated. The sheet resistance of sample 1 was higher than those of samples 2 and 3, although during water electrolysis, a high current density was observed due to the nanostructure of the IrO₂ catalyst. In addition, the structural stabilities of Nafion and Aquivion membranes up to 150 °C were investigated by using small angle X-ray scattering (SAXS). The polymer structures of Nafion and Aquivion membranes were stable up to 80 °C, whereas the crystalline domains grew significantly above 120 °C. In other words, the initial polymer structure did not recover after the sample was heated above the glass transition temperature.