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The Role of Water in Vapor-fed Proton-Exchange-Membrane Electrolysis

Fornaciari, Julie C and Gerhardt, Michael R and Zhou, Jie and Regmi, Yagya N and Danilovic, Nemanja and Bell, Alexis T and Weber, Adam Zev (2020) The Role of Water in Vapor-fed Proton-Exchange-Membrane Electrolysis. Journal of the Electrochemical Society. ISSN 0013-4651

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Abstract

Water-vapor fed electrolysis, a simplified single-phase electrolyzer using a proton exchange membrane electrode assembly, achieved >100 mA/cm2 performance at <1.7 V, the best for water-vapor electrolysis to date, and was tested under various operating conditions (temperature and inlet relative humidity (RH)).To further probe the limitations of the electrolyzer, a mathematical model was used to identify the overpotentials, local water activity, water content values, and temperature within the cell at these various conditions. The major limitations within the water-vapor electrolyzer are caused by a decreased water content within the membrane phase, indicated by increased Ohmic and mass transport losses seen in applied voltage breakdowns. Further investigations show the water content (λ, mole of water/mole of sulfonic acid) can decrease from 13 at low current densities down to 6 at high current densities. Increasing the temperature or decreasing RH exacerbates this dry-out effect. Using our mathematical model, we show how these mass transport limitations can be alleviated by considering the role of water as both a reactant and a hydrating agent. We show that low cathode RH can be tolerated as long as the anode RH remains high, showing equivalent performance as symmetric RH feeds.

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