Strategies for bubble removal in electrochemical systems

Bubbles are known to affect energy and mass transfer in gas-evolving electrodes, including those in water splitting, chlorine generation, direct methanol fuel cells, and carbon dioxide generation. As bubbles vigorously evolve in electrochemical reactions, undesired blockage of active sites and ion conducting pathways result in serious energy losses. Since new advances are made with the development of new theories, materials, and techniques, this review discusses the recent works on promoting bubble removal in electrochemical systems with the aim of guiding and motivating future research in this area. We first provide the mechanism of bubble evolution in electrochemical systems and the resultant overpotentials in detail. Then, recent advances in mitigating bubble issues are presented from the perspectives of passive and active strategies. Passive strategies act on the macro- and micro-structures of the electrode, surface wettability, and electrolyte properties. Active strategies employ out-fields, including flowing electrolytes, acoustic fields, magnetic forces, and photothermal effects, to guide bubbles out of reaction sites aiming at high reaction rates, whereas external energy is needed. Finally, the pros and cons of both strategies and future outlooks are presented. This review leads to design guidelines for high-performance gas-evolving electrochemical systems.