(115b) Modeling the Effect of Material Properties on Liquid Alkaline Water Electrolyzer Performance

Liquid alkaline water electrolyzers (LAWEs) have been used to produce H₂ in industry using excess electricity since the early 1900’s. These devices benefit from highly-stable and inexpensive porous nickel electrodes that are used to mediate the anodic oxygen evolution reaction (OER) and cathodic hydrogen evolution reaction (HER). However, LAWEs rarely achieve high reaction rates (i.e., current densities) because of high Ohmic resistances in the porous separator, slow reaction kinetics, and a reduction in nickel catalyst surface area caused by H₂ and O₂ bubble formation during operation. New porous electrodes, separators, and operational philosophies must be developed to manage these issues and increase the current density of LAWEs.

This talk will discuss a 1D continuum model of a LAWE that combines the Nernst-Planck equation with Butler-Volmer kinetics to resolve pH and conductivity gradients in LAWEs. The simulation deconvolutes experimentally-measured applied voltages into kinetic, Ohmic, and concentration polarization losses. The model was applied to several data sets to explore the effect of nickel foam properties (i.e., specific surface area and porosity) and separator resistance on the current density of LAWEs. The model shows that the pore diameter and porosity of nickel foams critically impacts the electrochemically-active surface area through both geometric and bubble coverage effects. The separator was found to contribute most significantly to the total Ohmic resistance, but this resistance can be reduced by decreasing the separator tortuosity and thickness. This talk will provide an overview of these structure-property-performance relationships that can be used to inform the design of advanced electrodes and separators for LAWEs.