Impact of electrode surface texturing on hydrogen bubble dynamics during proton exchange membrane water electrolysis

Abstract

Water electrolysis systems are vital for sustaining human life during long-term space exploration missions. The main obstacle to the in-space operation of a water electrolysis system is the near-absence of buoyancy forces, impeding the detachment of hydrogen and oxygen bubbles from the electrodes and further complicating gas management, a crucial factor for efficient operation even in terrestrial applications. One of the most promising approaches to mitigate this problem is the micro- or nanostructuring of the electrode surfaces. Via surface structuring, the electrochemically active surface area can be enlarged and hydrophilicity increased, leading to easier detachment of gas bubbles. Additionally, bubble nucleation can be improved and bubble coalescence reduced. In this study, five pairs of laser-textured electrodes are manufactured, characterized and analyzed in terms of their performance and their influence on the bubble dynamics of the produced hydrogen gas. All textured electrodes achieve a performance enhancement over the unmodified surface (10% to 45% increase in current density for the same supply voltage). Gas production experiments prove that an increase in current density at a given voltage directly corresponds to a rise in production rate and, hence, in electrolysis performance. Significant differences in the bubble size distribution are observed on the different surfaces, as well as at different supply voltages. Distribution shapes and parameters (mean and standard deviation) remain mostly constant over time. Bubble rise velocities are significantly influenced by the entrainment of flow by the rising bubble plumes. Bubble growth after detachment is proven to be diffusion-controlled, and mainly determined by the degree of supersaturation close to the electrodes. This study proves that modification of the electrode surface morphology influences the performance of PEM systems by alteration of the bubble behavior during operation.