Unidirectional bubble transportation on slippery micro-cone array electrodes enables spontaneous 99.99% gas separation in membrane-less water electrolysis†

Abstract

Membrane-less electrolysis is utilized for many gaseous chemical productions. However, the problems of gas mixing and low energy efficiency remain huge obstacles for its practical application. Herein, we have prepared a biomimetic electrode by three-dimensional (3D) printing technology, featuring a “slippery aerophobic” surface and micro-cone array structure with tunable tilting angles. These electrodes enable the bubbles that are generated at the cone tip to “roll-up” rapidly along the electrode towards its base, rather than being directly released into the electrolyte, resulting in gas mixing. The unidirectional bubble transportation behavior was understood by a collective analysis of the Laplace pressure on cones, bubble buoyancy and irreversible hysteresis. As a proof of concept, we employed this biomimetic electrode in membrane-less water electrolysis. At a current density of 240 mA cm⁻², we achieved the separation of H₂ and O₂ gases with >99.99% purity even with an electrode distance as short as 1.5 mm. This work demonstrated the efficiency of precisely manipulating bubble transportation in membrane-less electrolysis that does not rely on expensive membranes.