Relationship between Electrolyte and Overpotential Component in Anion Exchange Membrane Water Electrolysis

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 (<pH14) is often used as the supporting electrolyte. 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).