Modeling Contact Resistance and Water Transport within a Cathode Liquid-Fed Proton Exchange Membrane Electrolyzer

Abstract

Conventional proton-exchange membrane (PEM) water electrolyzers use thicker membranes (>175 μ m) than their PEM fuel cell counterparts (<25 μ m), which reduces hydrogen crossover but also reduces electrolyzer efficiency due to the increased resistance. Reduction of hydrogen crossover is critical in conventional systems to avoid buildup of hydrogen in the anode above the lower flammability limit. New concepts for operating PEM water electrolyzers are emerging, such as the patented concept involving liquid water supply at the cathode while operating the anode with air, which reduces the safety concern related to hydrogen crossover using thin membranes. Experimental work has demonstrated the viability of this approach, but open questions remain regarding the interplay between water transport, water consumption, and cell performance, as well as identifying the components and material properties that enable high performance. In this work, a physics-based computational model of a cathode-fed PEM water electrolyzer was developed. The model highlights the importance of limiting contact resistance and explores the effect of cell compression on non-uniformity of current distributions. Sensitivity studies found that membranes up to 50 μ m thick can be used without significant water transport limitations.