Electrolytic Solution of Anion Exchange Membrane Electrolyzer

Abstract

In the promotion of the use of renewable energy, the role of hydrogen (H2) as the energy carrier is a key for buffering the fluctuating and/or intermittent power from renewable energy sources. As the hydrogen production device from renewable energy, a water electrolyzer is the simplest and most realistic. Among several options, PEM water electrolysis is suitable for intermittent power input, and also capable of operation at higher current density (> 3 A cm-2). However, a major drawback of PEM electrolysis is its high capital cost per power input compared to conventional alkaline electrolysis. The acidic environment of PEM limits the type of material that can be used for cell components (i.e., bipolar plates and current collectors) to titanium (Ti) and that of the catalyst to platinum-group metals (PGMs). The use of these precious materials is a major reason for the high stack cost of a PEM electrolyzer. When a membrane performing under alkaline (basic) conditions is applied to the electrolyte, the material restriction for the cell components can be relaxed. In particular, the material Ti of the bipolar plates can replaced by a cheaper material such as stainless steel, which would significantly reduce the stack cost, because the cost share of Ti-bipolar plates is significant in the total stack cost of PEM electrolyzer. An alternative material for the electrolyte is an anion exchange membrane (AEM) that has high internal pH. When such an AEM is applied as the electrolyzer based on the same structure as the PEM electrolyzer, a low-capital-cost device is possible and still retain the advantages of PEM electrolysis. In this study, in order to confirm the potential of AEM electrolysis under mild alkaline conditions (pH ≤ 12), the effect of species and concentration of electrolytic solution on the performance of AEM electrolysis was experimentally examined, where DI water, KOH (10mM), and K2CO3 of different concentrations (0.1, 1, and 10 wt. %) were applied for the electrolytic solution. In the cell, Pt/C was used as the cathode catalyst and CuCoOx as the anode catalyst. Furthermore, to examine the effect of structure of anode current collector (i.e., gas diffusion layer; GDL) on the performance, either nickel (Ni)-foam or Ni-felt was applied to the cell. In addition to current-voltage (i-V) characteristics, the Faraday (current) efficiency and hydrogen cross-permeation was also evaluated based on the experimental data.