Calculation of Oxygen Potential Profile in Proton-Hole Mix Conductive Electrolyte and its Application for Evaluation of Practical Cells

Abstract

In this work, IV characteristic and efficiency of protonic ceramic fuel cells and electrolysis cells were discussed based on the oxygen potential profile in mix conductive electrolyte. In protonic electrolyte such as barium zirconate, which exhibits partial hole conductivity in oxygen atmosphere, oxygen potential profile shows a steep slope where hole conductivity is low. As the result, hole blocking layer becomes extremely thin and the rest of the electrolyte shows a significant hole conductivity. Therefore, current leakage cannot be ignored even when the electrolyte material shows quite low electronic conductivity in one side of the electrolyte. When electronic leakage is significant, the analysis of electrochemical measurements becomes complicated. In such case, focusing on the net ionic current is a useful approach to evaluate the cell characteristics. Considering the effect of electrode polarization on the oxygen potential gap at electrode/electrolyte interface, electronic leakage becomes more serious in electrolysis mode. The simulation results showed that both improvement of ionic transportation number of electrolyte and reduction of polarization resistance of oxygen electrode are critical to achieve high efficiency in electrolysis cells.