Electro-Osmotic Drag Coefficients in Proton Exchange Membrane Water Electrolysis: Measurement Technique Validation and Investigation of Nafion™ Membranes

A fundamental understanding of water and gas transport is crucial for continued improvements of electrolysis systems. This work demonstrates a technique to measure electro-osmotic drag in proton exchange membrane water electrolysis (PEMWE) cells. The method was validated using repeated testing of several variations of Nafion™ membranes. The effect of temperature, thickness, membrane fabrication route, current density, and equivalent weight on electro-osmotic drag coefficients were explored. Specific conclusions can be drawn from the data for this class of perfluorinated polymer membranes. Notably, temperature, membrane fabrication route, and equivalent weight were all found to have meaningful impact on electro-osmotic drag. The lowest electro-osmotic drag coefficients observed were just below 3 water molecules per proton and the highest electro-osmotic drag coefficients were just above 5 water molecules per proton. This represents up to a ∼70% increase in water flux and is expected to significantly impact hydrogen and oxygen flux across the cell. The observed electro-osmotic drag coefficients scaled proportionally to the water uptake of the membranes studied, with increased water uptake leading to higher electro-osmotic drag coefficients. Both the method of measuring electro-osmotic drag and the observed results in this paper are key findings that help quantify water flux in operating PEMWE cells.