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

Abstract

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.

Crosslinked Sulfonated Polyphenylsulfone (CSPPSU) Membranes for Elevated-Temperature PEM Water Electrolysis

“…The catalytic electrode for oxygen evolution on the anode side (sample 1) was provided by Japan Carlit Co. Sample 1 had good catalytic electrode properties in the previous paper [33]. The cathode electrode for hydrogen generation was a Pt/C catalyst electrode (EIWA co. ltd. Tokyo, Japan), which was prepared by coating 0.3 mg/cm 2 of Pt (20 wt% Pt/C, JM) on a carbon GDL (SGL 25BC, Sigracet ® Meitingen, Germany).…”

“…The aim is to reduce the cost and improve the performance. Fluorinated electrolytes (PFSA) [36], such as Nafion [6,12,13,15,33,37], Aquivion [6,24,33,38], and radiation-grafted ethylene tetrafluoroethylene (ETFE) membranes [39,40], have been reported to exhibit high proton conductivities, high chemical stabilities, and water electrolysis properties. Non-fluorinated hydrocarbon electrolyte membranes, such as sulfonated poly(ether ether ketone) (SPEEK) composite [41,42], polyethylene oxide grafted polyether sulfone (PES-g-PEO) [43], sulfonated polysulfone (SPSf) [44], sulfonated poly(phenylene sulfone) (sPPS) [45], and sulfonated poly(arylene ether sulfone) [46], have been reported.…”

“…At the same time, higher operating temperatures (100-200 • C) are thought to be one way of increasing the efficiency of PEMWE. Moreover, the higher temperatures should improve the overvoltage of the entire cell due to the kinetic and thermodynamic advantages of the catalytic electrodes in water splitting, which improve the catalytic electrode activity [6,12], the conductivity of the electrolyte membrane [33], and the interfacial resistance between the electrolyte membrane and the catalytic electrode. Currently, water electrolysis characteristics at temperatures above 100 • C have been reported, but in those experiments, mostly fluorinated electrolyte membranes, especially Nafion membranes [33][34][35][47][48][49][50][51][52], are used.…”

“…Moreover, the higher temperatures should improve the overvoltage of the entire cell due to the kinetic and thermodynamic advantages of the catalytic electrodes in water splitting, which improve the catalytic electrode activity [6,12], the conductivity of the electrolyte membrane [33], and the interfacial resistance between the electrolyte membrane and the catalytic electrode. Currently, water electrolysis characteristics at temperatures above 100 • C have been reported, but in those experiments, mostly fluorinated electrolyte membranes, especially Nafion membranes [33][34][35][47][48][49][50][51][52], are used. However, the application of fluorinated electrolyte membranes at temperatures above 100 • C is difficult for practical use because of the degradation of the thermal, mechanical, and chemical properties [33,53,54].…”

“…Currently, water electrolysis characteristics at temperatures above 100 • C have been reported, but in those experiments, mostly fluorinated electrolyte membranes, especially Nafion membranes [33][34][35][47][48][49][50][51][52], are used. However, the application of fluorinated electrolyte membranes at temperatures above 100 • C is difficult for practical use because of the degradation of the thermal, mechanical, and chemical properties [33,53,54]. In other words, the durability of these membranes is lower at higher temperatures.…”