Analysis of Mass Transfer in Electrochemical Pumping Devices

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Considering the environmental challenges posed by traditional energy systems, we must strive to seek out innovative strategies to sustainably meet today’s demands for energy and quality of life. Energy systems using electrochemical (EC) energy conversion methods may help us to transition to a more sustainable energy future by providing intermittent renewable energy storage and improving building energy efficiency. EC pumping devices are a novel technology that use chemical reactions to pump, compress, or separate a given working fluid. These devices operate without any moving parts. Unlike mechanical pumps and compressors, they operate silently, producing no vibrations and requiring no lubrication. In this dissertation, I investigate EC pumping devices for use in two applications: ammonia EC compression for intermittent renewable energy storage and EC dehumidification for separate sensible and latent cooling.

Hydrogen fuel cells are a promising technology for on-demand renewable power generation. While storage of pure hydrogen fuel remains a problem, ammonia is an excellent hydrogen carrier with far less demanding storage requirements. EC ammonia compression opens the door to several possibilities for separating, compressing, and storing ammonia for intermittent power generation. Using the same proton exchange membranes commonly used in fuel cells, I demonstrated successful ammonia compression under a variety of operating conditions. I examined the performance of a small-scale ammonia EC compressor, measuring the compression and separation performance. I also conducted experiments to investigate the steady-state performance of a multi-cell ammonia EC compressor stack, observing a maximum isothermal efficiency of 40% while compressing from 175 kPa to 1,000 kPa. However, back diffusion of ammonia reduced the amount of effluent ammonia by as much as 67%.

Dehumidification represents a significant portion of air conditioning energy requirements. Separate sensible and latent cooling using EC separation of water may provide an energy efficient thermal comfort solution for the hot and humid parts of the world. I conducted experiments of several EC dehumidifier, considering both proton exchange and anion exchange processes. Diffusion of the working fluid was significant in this application as well. I observed a maximum Faradaic efficiency for dehumidification of 40% for a 50 cm2 cell using an anion exchange membrane under the most favorable case. I developed a novel open-air EC dehumidifier prototype. To alleviate the back diffusion issue, I investigated a method for mass transfer enhancement using high-voltage fields. I also developed a numerical model to simulate the performance of the EC dehumidifier devices, predicting the experimentally measured performance to within 25%.