Impact of nickel electrode geometry on the electrochemical performance and bubble dynamics of a zero-gap alkaline electrolyzer

This study examines the impact of 2D perforated plates and 3D-structured nickel electrodes on electrochemical performance and bubble behavior in a zero-gap alkaline water electrolyzer. 2D nickel electrodes with 0.5, 1.0, and 2.0 mm perforation diameters exhibit similar area-ohmic resistance of ∼0.55 Ω cm2 at 0.4 A/cm2, while a 3D-structured electrode with pillar features achieves the lowest ohmic resistance of 0.33 Ω cm2 at 0.4 A/cm2. Video analysis reveals microbubble coalescence and detachment dynamics, correlating with electrochemical performance. Most bubbles have a diameter under 400 μm, making 2D perforated plates with perforations of 0.5 mm or larger comparable in performance. Bubbles trapped in the imperfect zero-gap may significantly contribute to the total ohmic resistance. When perforations are smaller than the average bubble diameter, bubbles cannot escape, leading to increased ohmic resistance. The good performance of the electrode with pillar features is attributed to effective bubble management in a close to zero-gap configuration. The findings underscore the potential of 3D structured electrodes to enhance efficiency, reduce material usage, and enable green hydrogen production using non-noble materials at high current densities.