(Invited) Electrochemical Fuels Production Using High Temperature Alkaline Electrolytes

Abstract

Anion exchange membranes (AEMs) have potential applications in a variety of energy conversion technologies (e.g. fuel cell, electrolyzer), due to enabled adoption of non-precious metal catalysts. However, these polymer-based AEMs generally have poor stability, particularly at elevated temperatures (> 80 ℃), limiting their viable applications. On the other hand, operating electrochemical cells at higher temperature can improve the electrode kinetics, simplify heat management, and increase the system efficiency. Here we report an alkaline system that utilizes molten alkaline (e.g., lithium, sodium, or potassium hydroxide) impregnated into a porous metal oxide (MO) matrix as the electrolyte. The operating temperature can vary from 250 to 500 °C, depending on the category and ratio of each individual electrolyte. A key factor that will influence the success of this technology is the microstructures of the porous oxide matrices. Their thickness, porosity, pore size and structure largely determine whether they can successfully retain molten hydroxides in their pores, particularly over extended period of time. The single and binary hydroxide with 25 wt% (e.g., MO-LiOH-25 and MO-LiOH-NaOH-25) electrolyte showed OH- conductivity of 0. 15 S.cm-1 and 0.5 S.cm-1, respectively, at 500 ℃, demonstrating significant advantage of this alkaline electrolyte. As two applications, water electrolysis and electrochemical synthesis of ammonia using this composite electrolytes are being tested and will be reported. Cell components and process conditions will be optimized to maximize the performance of the electrochemical cells. Acknowledgements Financial support from DOE EERE Fuel Cell Technology Office under award # DE-EE0007644