Magnetohydrodynamic Bubble Removal for Water Electrolysis in Reduced-Gravity Environments

Water electrolysis is an essential electrochemical process for oxygen production in space and high-purity hydrogen production on Earth. As with all gas-evolving liquid phase reactions, the presence of bubbles over the electrodes increases cell resistivity and hinders mass transport of the liquid electrolyte to the electrode surfaces. On Earth, efficiency losses due to the presence of bubbles can be as high as 30%. In a reduced-gravity environment, the lower buoyancy force will delay bubble detachment further, leading to additional efficiency losses. Among a variety of methods proposed and in use for accelerating bubble evacuation, magnetohydrodynamic pumping via a magnetically induced Lorentz force has shown promise in controlled lab trials. In this paper, we describe the modeling and testing of a magnetohydrodynamic alkaline water electrolysis architecture where the magnetic field is produced by off-the-shelf rare-Earth N52 permanent magnets arranged in a Halbach pattern. The arrays are located just behind the electrodes to amplify the strength of the field and facilitate follow-on scale-up efforts. Benchtop tests of three magnet sizes at current densities between 10-500 mA/cm2 show little or no improvement in chronopotentiometric trials with magnetic forcing aligned with and against gravity. However, potentiostatic EIS data show a 34.5% reduction in diffusion resistance and a 132.5% increase in diffusion capacitance, which are promising mass transport benefits that hint at potential benefits for improved magnetic configurations.