Visualization of Bubble Behavior on Hydrophobic Coated CL in PEM Water Electrolysis Cell

Abstract

Due to the need for a new energy infrastructure, water electrolysis technology is receiving increased attention (1), (2). One of the serious problems is management of generated oxygen bubbles which inhibit water supply to the CL. Therefore, bubble behavior was observed on three types of CL with hydrophilic and hydrophobic surface by using a high-speed camera. A single cell, shown in Fig. 1, was used for observing oxygen bubble behavior. Nafion-117 was used as PEM, and IrOx and Pt/C was used anode and cathode catalyst, respectively. Sinterd Ti with Pt plating was used for anode porous transport layer (PTL). Three types of PTFE coated CL were prepared: (a) no coating, (b) coated all and (c) coated half. High-speed camera (Redlake MASD, HS-1), magnifying glass (Hirox, cx-10c) and objective lens (Hirox, OL-35) were used. Electrochemical measurement system (Bio-Logic, SP-240) was used for applying voltage, and the voltage sweep was performed at a rate of 4 mV/s until the cell voltage turned from 0 V to 2.5 V. The current density at voltage of 2.5 V was about 4200 mA/cm2 for CL (a), 1200 mA/cm2 for CL (b) and 3700 mA/cm2 for CL (c). A big bubble covering entire PTL hole was visualized in Fig. 2 (b). In Fig. 2 (c), smaller bubbles appeared from left PTFE uncoated area were merged into a bigger bubble, which stayed on right PTFE coated area. The size of bubbles staying on the edge of PTL-holl in Fig. 2 (a) was smaller than those of (b, c). The results may suggest that the CL (b) deteriorated the cell performance because of the bubble covering entire reaction area. From this experiment, we could control stagnation of bubbles on CL by PTFE treatment. There may be some possibilities that controlling bubble stagnation make some differences on cell performance.Acknowledgements: This study was based on results obtained from a project (JPNP14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO).Reference:(1) G. Bender, et al, Int. J. Hydrogen Energy, 44 (2019), 9174-9187(2) S. Mitsushima et al, ECS Meeting s, MA2019-02 (2019), 1715. Figure 1