Porous Substrate\nOptimization for Efficient Water\nElectrolysis: Uncovering Electrocatalysts, Electrolyte, and Bubble\nDynamics Effects

Water electrolysis\nis a promising technique for producing\nhydrogen,\na clean energy carrier essential for achieving a sustainable society.\nReducing costs to meet the hydrogen demand is anticipated through\noperations at a high current density. However, excessive bubble formation\nduring high-current operations deteriorates the electrolysis performance.\nEngineering substrates could help minimize additional overpotential\nwhile maintaining sufficient electrocatalyst amounts. In this study,\nwe discuss optimizing porous substrates to maximize the oxygen evolution\nreaction (OER) and overall single-cell performance, using a Ni mesh\nmodel structure with or without NiFeO<sub><i>x</i></sub> catalyst decoration. The numerical simulation was conducted to reveal\nthe contribution of an increase in electrode thickness, which augments\nelectrocatalyst quantities. The calculation predicts that the OER\noverpotential decreases with the stacking number of electrodes. This\nestimation aligns with experimental results when the current density\nis 10 mA cm<sub>geo</sub><sup>–2</sup>. However, this monotonic\ntrend was not observed at 800 cm<sub>geo</sub><sup>–2</sup>, showing the optimal thickness that offers the lowest potential.\nThe optimal thickness depends on the electrocatalyst’s identity;\nelectrocatalysts with a lower Tafel slope (NiFeO<sub><i>x</i></sub> over Ni) require thinner electrodes for maximum performance.\nWe conducted optical bubble characterizations to track the primary\nbubble size. When comparing bubble size with the mesh aperture size,\nthe correlation between bubble accumulation within the stacked meshes\nand the increase of overpotential at thicker electrodes becomes evident.\nOur study underscores the importance of the simultaneous development\nof electrocatalysts, electrolytes, and substrates.