Iron-Based Electrode Structures for Ammonia Electrosynthesis Cells with Proton-Conducting Ceramic Electrolytes

Abstract

Ammonia electrosynthesis was conducted using proton-conducting ceramic electrolysis cells in a single chamber supplied with mixed N2 and H2, to determine the active electrode regions for the electrochemical promotion of catalysis (EPOC). Cells with Fe-based cathodes of either a metal, cermet, or mixed ionic-electronic conductor (MIEC) structure were compared, to assess whether the triple-phase boundaries (TPBs) or the Fe catalyst surfaces are more effective for ammonia synthesis. Upon cathodic polarization at 600˚C, high ammonia formation rates on the order of 10−8 mol s−1 cm−2 were obtained with both Fe metal and Fe-BaZr0.8Y0.2O3 (Fe-BZY) cermet cathodes. Comparisons of the three electrode structures suggest that when H2 is also supplied to the cathode, ammonia formation occurring on bulk Fe surfaces leads to a greater promotional effect than that at TPBs. There also remains a possibility that the interfacial layer formed at the cathode-electrolyte interface due to cation interdiffusion aids ammonia formation.