Efficient Alkaline Oxygen Evolution at Industrial Current Densities with Hierarchical Electrode Architecture Overcoming Mass Transport Limitations

Alkaline oxygen evolution reaction (OER) crucial for green hydrogen production can be primarily enhanced by electrode nanostructuring to increase active-site density and boost catalytic activity. However, above 0.5 A cm^–2, this enhancement is limited by insufficient O₂ transport due to the challenge of counteracting Marangoni-stabilized retention of large O₂ bubbles, and impaired OH^– transport resulting from excessive nucleation-site density. Herein, we demonstrate a three-tier hierarchical electrode architecture that overcomes the mass transport limitations while enhancing catalytic activity via nanocrystalline NiFe layered double hydroxide nanosheets. Pore confinement-induced Laplace pressure gradients enforce bubble self-ejection, which reduces departure diameters to sub-50 μm and bubble ohmic overpotential by 61.5%. Confining nucleation to single nanocavity in microcavities with large spacings reduces nucleation density by 89.6% and eliminates OH^– transport blockage. The proposed approach enables ultralow transport and total OER overpotentials of 62 mV and 280 mV at 1.0 A cm^–2, dropping by 75.5% and 46.1%, respectively.