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 cut-off 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.