Porous Substrate Optimization for Efficient Water Electrolysis: Uncovering Electrocatalysts, Electrolyte, and Bubble Dynamics Effects

Water electrolysis is a promising technique for producing hydrogen, a clean energy carrier essential for achieving a sustainable society. Reducing costs to meet the hydrogen demand is anticipated through operations at a high current density. However, excessive bubble formation during high-current operations deteriorates the electrolysis performance. Engineering substrates could help minimize additional overpotential while maintaining sufficient electrocatalyst amounts. In this study, we discuss optimizing porous substrates to maximize the oxygen evolution reaction (OER) and overall single-cell performance, using a Ni mesh model structure with or without NiFeOx catalyst decoration. The numerical simulation was conducted to reveal the contribution of an increase in electrode thickness, which augments electrocatalyst quantities. The calculation predicts that the OER overpotential decreases with the stacking number of electrodes. This estimation aligns with experimental results when the current density is 10 mA cmgeo–2. However, this monotonic trend was not observed at 800 cmgeo–2, showing the optimal thickness that offers the lowest potential. The optimal thickness depends on the electrocatalyst’s identity; electrocatalysts with a lower Tafel slope (NiFeOx over Ni) require thinner electrodes for maximum performance. We conducted optical bubble characterizations to track the primary bubble size. When comparing bubble size with the mesh aperture size, the correlation between bubble accumulation within the stacked meshes and the increase of overpotential at thicker electrodes becomes evident. Our study underscores the importance of the simultaneous development of electrocatalysts, electrolytes, and substrates.