Deciphering Structure-Bubble-Mass Transfer Relationships in Water Electrolysis Through Electrode Morphology...

Unraveling the regulation of electrode local geometric curvature on bubble dynamics is essential to mitigate mass transport losses for the oxygen evolution reaction (OER). Conventional studies emphasize high surface area and porosity while neglecting local geometric curvature and connectivity. Here we identify local electrode curvature as a physically grounded descriptor. Positive curvature at sharp tips concentrates the electric field, raises local gas supersaturation, and reduces the three-phase contact line pinning, which confines growing bubbles and enables their release at a small size. Flat or concave surfaces lack these effects and trap gas. To validate this, positive curvature (κ₊) nanoneedles (NN), near-zero curvature (κ₀) nanosheets (NS), and negative curvature (κ_-) microporous (MP) electrodes are developed. At 200 mA cm^-2, in situ high-speed visualization demonstrates that NN exhibits a departure diameter of 45 µm, alongside the minimal mass transport overpotential (158.52 mV). NS delivers moderate bubble behavior and an intermediate overpotential (248.04 mV), while MP suffers severe bubble pinning despite a moderate 60 µm bubble size, resulting in the highest mass transport overpotential (252.98 mV). This work verifies that open convex architectures govern bubble kinetics far beyond porosity, providing universal design guidelines for high-performance OER electrocatalysts.