Cassie-impregnated interface design enables efficient O₂ bubble mass transfer in NiCo₂O₄ array electrodes

Three-dimensional array structures are recognized as hydrophilic and gas-repellent architectures for water electrolysis electrodes. In reported studies, the interfacially accelerated bubble detachment process is generally attributed to the role of the gas–liquid–solid three-phase contact line under the ideal Wenzel model, while in-depth investigations into bubble dynamics under the practically occurring Cassie-impregnating mode remain scarce. In this study, a stable Cassie-impregnating wetting state was constructed and optimized via regulation of the depth in NiCo₂O₄ nanowire arrays. As the array depth increases from 1.43 to 4.14 μm, the wettability and gas-repellent performance exhibit a “volcano-type” trend, with a maximum underwater bubble contact angle of 150° and a minimum bubble adhesion force of 9.51 μN. Dynamic bubble statistics reveal that at 100 mA·cm⁻², the optimized NiCo₂O₄ nanowire array delivers a high O₂ bubble generation rate of 107 cm⁻²·s⁻¹ for bubbles with an average size of ~ 120 μm. The mass transport overpotential for the oxygen evolution reaction (OER) on the NiCo₂O₄ nanowire electrode is reduced to 157 mV at 300 mA·cm⁻². Moreover, the anion exchange membrane water electrolyzer delivers a cell voltage of only 1.81 V at a current density of 1000 mA·cm⁻², while maintaining stable operation for more than 400 h.