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.

Improving Performance and Durability of Low Temperature Direct Ammonia Fuel Cells: Effect of Backpressure and Oxygen Reduction Catalysts

“…Recently, low temperature direct ammonia fuel cells (DAFCs) have attracted increasing attention as a possible electrochemical powerplant for carbon-neutral transportation applications due to several significant benefits of ammonia, including high volumetric energy density and the availability of large-scale infrastructure for its production, transmission, dispensation and storage. [1][2][3][4] However, DAFCs are still in the early phase and major issues are their low performance and poor durability. Early reported works suggest that DAFCs can only provide peak power densities below 10 mW cm −2 , [5][6][7][8][9] which are considered impractical for use onboard a vehicle.…”

Liquid water transport and management for fuel cells

“…(7,12). Early work has shown the potential for using sliding-angle-based adhesion measurements to approximate droplet detachment as well as capture effects due to surface wetproofing, liquid flow rate variation, vibration, and aging (12,(21)(22)(23). Several direct and indirect methods exist to investigate liquid-gas two-phase flow in fuel cell reactant channels.…”

A High-Performance 75 W Direct Ammonia Fuel Cells Stack

“…This recognition is based on the fuel's high energy density, large-scale global production, extensive existing infrastructure, and low cost per unit energy [4][5][6][7][8][9][10][11] . The recent attention to ammonia/air fuel cell power sources, is explained by this rising interest in ammonia as a non-carbon, alternative fuel for transportation [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] . Low-temperature direct ammonia fuel cell (DAFC) has two important features of low temperature operation and direct use of the fuel stored on board as the anode feed stream.…”