Decoupling of Reaction Overpotentials and Ionic Transport Losses within 3D Porous Electrodes in Zero-Gap Alkaline Electrolysis Cells

Designing more efficient and productive alkaline electrolysis (AE) cells requires the development of electrode microstructures that facilitate mass transport and reduce associated ionic transport losses within the electrodes. Here we propose a method, relying on a minimum of three reference electrodes, that allows to decouple the Galvani potential losses (GL) associated with ionic migration within each of the electrodes from the overall electrode overpotential. This provides additional insight along with the separation of the voltage losses within the anode, cathode, and separator that is also achieved during zero-gap operation at industrially relevant conditions. Different Nickel electrode structures have been investigated to assess the effect of thickness, surface area, and porosity on the GL within the electrodes. The GL in the anode are higher than in the cathode for the same electrode structure and decrease upon decreasing electrode thickness. Reducing the cathode thickness, while maintaining the same specific surface area, improves performance more compared to the anode. Moreover, electrodes with large pore diameter (0.43 mm) were observed to facilitate the oxygen evolution reaction (OER), whereas electrodes with small pore diameter (0.23 mm) and large surface area are beneficial for the hydrogen evolution reaction (HER). Overall, the proposed methodology provides vital information in guiding the microstructural optimization of electrodes for advanced alkaline electrolysis cells.