Multi-Scale Simulations of Bubble Transport in an Alkaline Water Electrolyzer

Abstract

The existence of bubbles can lead to the loss of performance by decreasing the electrochemically active surface area and disrupting the transport of hydroxide ions. These effects caused by the bubbles have yet to be sufficiently clarified. A comprehensive understanding of the mechanisms of dynamics inside an electrolyzer from the molecular scale up to the whole electrolyzer scale is needed. Furthermore, establishing relations between these dynamics at a wide range of scales is important. In this study, numerical simulations of bubble transport coupling fluid dynamics, mass transport and electrochemical reactions were conducted on micro and macro scales, respectively. The micro scale bubble simulation (Fig. 1(a)) incorporates the concentration field of the chemical species into the numerical model and deals with how bubbles grow on and detach from an electrode. In this model, the chemical species generated by the electrochemical reactions dissolve into the liquid phase, and their transfer into the gas phase leads to bubble growth. Since the spatial size distribution of the bubbles can be one of the factors that affect electrolysis performance, in the macro scale bubble simulation (Fig. 1(b)), we study how different sizes of bubbles are transported and distributed inside the electrolyzer. To simulate this phenomenon, a four-phase flow analysis is performed in which small, medium, and large diameters are selected as representatives of bubble diameters, and each is treated as a different phase.[Acknowledgements]This study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in Advancement of Hydrogen Technologies and Utilization Project (P14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO).Fig. 1 Simulation systems of bubble transport at (a) micro scale and (b) macro scale. Figure 1