Anion Exchange Membrane (AEM) water electrolyzer is expected to be the next generation water electrolyzer that can realize low cost and high performance. Because the ionic conductivity of AEM and catalytic activity cannot be sufficiently maintained if DI water is supplied to the anode in the current AEM water electrolyzer, a dilute solution of KOH or K 2 CO 3 ( We compared the performance of AEM water electrolysis when using K 2 CO 3 and KOH solution as the anode electrolyte, adjusted to a pH of around 12, and confirmed that K 2 CO 3 solution provides higher performance at this pH level [1]. On the other hand, many previous studies have shown that using a high pH electrolyte is useful for improving electrolysis performance. In this study, we conducted an electrolysis test by supplying a higher concentration of KOH solution to the anode, and re-examined the effects of the electrolyte solute and pH on electrolysis behavior. In the AEM water electrolysis tests, 1wt.%-KOH solution (pH=13.2) and 10wt.%-K 2 CO 3 solution (pH=11.8) were used as the anode electrolytes. Two types of cells were used in the AEM water electrolysis tests. One was Cell-1, with an electrode area of 25 cm 2 , and the other was Cell-2, with an electrode area of 1 cm 2 . In both cell tests, the electrolyte was supplied only to the anode, and the cathode was maintained in a dry state, and all tests were carried out at a cell temperature of 50ºC. In the test using Cell-1, current-voltage characteristics and dew point of the generated hydrogen were measured, and in the test using Cell-2, a reference electrode was inserted, and in addition to the current-voltage characteristics, overpotential separation of the anode and cathode was performed. The test results for both cells were examined, and the effects of the electrolyte solute and pH on the electrolysis behavior were considered. References [1] H. Ito et al., Int. J. Hydrog. Energy , 43, 17030 (2018).
Unitized reversible cell fuel cells (URFCs) have both fuel cell and water electrolysis device functions in a single cell-stack, making it possible to use them like secondary batteries that use hydrogen as an energy carrier. UFRCs are expected to save space, reduce maintenance, and improve operating rates compared to installing both devices separately, and are also considered suitable for use in special environments such as outer space. We have been conducting research and development to improve the performance of URFCs that use proton exchange membrane (PEM) as the electrolyte [1-3]. Porous materials made of carbon, such as carbon paper, are usually used as gas diffusion layers (GDLs) in proton exchange membrane fuel cells (PEMFCs). However, in the case of URFC, since the cathode of the fuel cell is also used as the anode for oxygen evolution in water electrolysis, carbon materials cannot be used for the GDL at oxygen electrode (cathode of fuel cell operation) due to the corrosive nature of the environment. For this reason, titanium non-woven fabric (Ti-felt) is usually used as the GDL in the oxygen electrode of URFC. Because the URFC oxygen electrode during fuel cell operation requires efficient removal of the produced water as the same as the cathode of PEMFC. a hydrophobic agent such as polytetrafluoroethylene (PTFE) is usually added to the GDL substrate to enhance the hydrophobicity of the GDL. Here, based on the findings obtained from research into PEMFC cathode GDLs, we examined the impact of improvements to the PTFE treatment method for Ti-felt GDLs on URFC performance (water electrolysis and fuel cell performance). We also attempted to change the porous structure of GDLs by impregnating titanium particles into the substrate of Ti-felt. The relationships between this porous structure of GDLs and URFC performance have been examined. References [1] C. M. Hwang et al., Int. J. Hydrog. Energy , 36, 1740 (2011). [2] C. M. Hwang et al., J. Power Sources , 202, 108 (2012). [3] H. Ito et al., Int. J. Hydrog. Energy , 40, 16556 (2015).
