An Experimental Method to Measure Electrokinetics of Oxygen Electrodes in High Temperature Solid Oxide Electrolyzers through Symmetrical Cell Configuration

Abstract

Using high temperature solid oxide electrolytic cells (SOECs) to make hydrogen from steam has thermodynamic advantages in efficiency and yield over its low temperature water electrolyzer counterparts. However, SOECs generally exhibit faster performance degradation than solid oxide fuel cells (SOFCs), thus presenting a major challenge to the technology scale up for mass production of hydrogen. One leading cause for the degradation is associated with the delamination of oxygen electrode (OE), particularly under high current densities or hydrogen production rate. In this presentation, we show our efforts to determine the experimental conditions under which OE can safely operate without delamination. We first show application of DC-biased electrochemical impedance spectroscopy (EIS) method to three-electrode symmetrical cells (STEC) to delineate OE polarization resistance RP and overpotential h as a function of current density (J) and time (t) under both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) operation modes. From this set of basic data, we extract intrinsic exchange current density (io) of the OE using the “low-field” approximation approach embedded in the classical Butler-Volmer equation. We then correlate the obtained io with time-to-delamination (TTD) defined by the time at which io become zero. We finally establish the analytical relationship between TTD and io for three typical operating current densities ranging from 0.5-1.5 A/cm2, from which the lifetime of SOEC is predicted at a specific H2-producing current density.