Aqueous Ammonia Wetting of Gas-Diffusion Media for Electrochemical Cells

Abstract

Increased interest in liquid ammonia (NH3) for hydrogen storage can be attributed to its lack of carbon, high energy density to volume and mass ratios (17.6 wt% hydrogen), a ubiquitous supply and distribution network, and lower cost. Recent progress in direct ammonia fuel cells for power generation, as well as ongoing work on the electrochemical synthesis of ammonia, motivate the need for fundamental investigations of aqueous ammonia interactions with electrode materials. Porous gas-diffusion media (GDM) play a large role in facilitating liquid, gas, and charge transport and are an inherent part of these technologies membrane electrode assemblies (MEA). This work characterizes how key wetting properties such as contact angle, advancing/receding contact angles, adhesion force, and breakthrough pressure are influenced by GDM wet-proofing, thickness, and structure. These properties are studied for aqueous ammonia solutions with 0, 10, 20, and 30 wt% NH3. The higher concentrations of NH3 along an electrode surface can lead to lower contact angles as surface tension is reduced. Wet-proofing with PTFE loadings up to 10 wt% increases hydrophobicity, while higher loadings have diminishing effects. The results are useful to those involved with modeling, design, construction, and optimization of these systems.