Bipolar Membrane Electrode Assemblies for Water Electrolysis

We present the first analysis of a zero-gap bipolar membrane water electrolyzer fed with liquid water. Our electrolyzers feature a high-pH environment for the oxygen evolution reaction and a low-pH environment for the hydrogen evolution reaction. The advantages of proton exchange membrane water electrolysis can be combined with those of anion exchange membrane water electrolysis by including a water splitting bipolar interface. First, we develop a KOH-free anion exchange membrane electrolysis cell. The cell's alkaline anode serves as an integral building block on the path to a bipolar system. In a second step, we use this building block to investigate the cell operation characteristics of various cell configurations. We study the cell performance as the bipolar interface is shifted progressively toward the anode. A bipolar membrane with and without a water splitting catalyst resulted in cell current densities of 450 and 5 mA cm–2 at cell voltages of 2.2 V, respectively. Upon moving the bipolar interface directly between the acidic membrane and the high-pH anode, we achieved current densities of 9000 mA cm–2 at cell voltages of 2.2 V. Our study demonstrates the potential of this water electrolysis configuration, which should be adopted for further scientific studies and may show promise for future commercial water electrolysis systems.