Boosting gaseous oxygen transport in a Zn-air battery for high-rate charging by a bubble diode-inspired air electrode

Fruitful efforts are made in designing effective zinc electrodes and electrocatalysts for rechargeable Zn-air batteries, while furious gaseous oxygen evolution on the air electrode during charging is rarely spotlighted. Herein, a bubble-diode concept from fluid dynamics is introduced to address the bubble issues. As a proof of concept, an expanded polytetrafluoroethylene membrane is selected as the substrate to construct the air electrode. In-situ observation and numerical simulation reveal that bubbles selectively penetrate from a less aerophilic side to a more aerophilic side in the designed electrode, but are blocked in conventional ones. Further, this electrode enables a Zn-air battery to exhibit an extremely high charging limiting current density of 94 mA cm-2 at the cutoff voltage of 2.2 V and long-lasting stability for over 600 cycles at 10 mA cm- 2. This work opens up a path to bubble removal from the electrode structure, favoring practical applications of gas-involving electrochemical technology.

Automated summary

Significant efforts have been made to design efficient zinc electrodes and electrocatalysts for rechargeable Zn-air batteries. However, the issue of excessive gaseous oxygen evolution during charging on the air electrode has been overlooked. In this study, a bubble-diode concept is introduced to address this problem. Using an expanded polytetrafluoroethylene membrane as the substrate, a novel air electrode is constructed that allows selective penetration of bubbles, resulting in high charging current density and long-lasting stability for the Zn-air battery. This research opens up new possibilities for practical applications of gas-involved electrochemical technologies.