Visualization of Bubble Behaviors in Flow Fields of PEM Water Electrolyzer

Abstract

Proton exchange membrane water electrolyzer (PEMWE) has been considered to be a promising technology for green hydrogen production, primarily because of its significant advantages in terms of high efficiency, high purity and fast dynamic response [1]. During its operation, hydrogen/oxygen evolves from the catalyst layer (CL), transports through the diffusion layer (DL) and then releases to the flow channel, forming various two-phase flow regimes, including bubbly, slug, annular, etc [2]. The presence of bubbles not only covers the electrode surface, but also blocks the water delivery, creating a large mass transfer resistance and even terminating the cell operation [3]. Another issue associated with bubble management is that the conventional parallel and serpentine flow-field configurations showed a poor self-pumping effect, exhibiting a mismatch between bubble evolution and removal rates [4]. To address this issue, therefore, some novel flow field designs have also been proposed in recent years, but the underlying mechanism how two-phase flow regime in flow-filed channels affects the electrolyzer performance is still not clear.In this work, we investigate the effect of two-phase behavior on the electrolyzer performance via a visualization approach, as illustrated in Figure 1. Our preliminary results have shown that an increase of water supply flow rate has insignificant effect on the electrolyzer performance even at high current densities. It is observed that with increasing the water supply rate, many bubbles are still covering the electrode surface, meaning that water cannot be effectively supplied to the CL. To address this issue, a degassing layer, with a thinner rib and a wider channel, is introduced to the flow field design, which is able to promote the self-pumping effect of gas bubbles. This novel design can facilitate the rapid detachment of bubbles from the electrode surface, providing more paths for the water penetration into the CL. Acknowledgement This work was fully supported by a grant from the National Natural Science Foundation of China (Project No. 52022003). References Razmjooei, T. Morawietz, E. Taghizadeh, et al, Increasing the performance of an anion-exchange membrane electrolyzer operating in pure water with a nickel-based microporous layer, Joule, 5(7) (2021) 1776-1799.Rakousky, U. Reimer, K. Wippermann, et al, An analysis of degradation phenomena in polymer electrolyte membrane water electrolysis, J. Power Sources, 326 (2016) 120-128.Villagra, P. Millet, An analysis of PEM water electrolysis cells operating at elevated current densities, Int. J. Hydrog. Energy, 44(20) (2019) 9708-9717.O. Majasan, J.I.S. Cho, I. Dedigama, et al, Two-phase flow behaviour and performance of polymer electrolyte membrane electrolysers: Electrochemical and optical characterization, Int. J. Hydrog. Energy, 43(33) (2018) 15659-15672. Figure 1