Electrochemical Performance of New Bilayer Oxygen Electrode for Reversible Solid Oxide Cells

Abstract

High-temperature solid oxide cells (HT-SOCs) have innate advantages over their low-temperature counterparts in efficiency and production rate since part of the chemical energy in the products comes directly from the heat and the operating current density (proportional to H2 production rate) is high. However, a major obstacle for HT-SOCs to be commercially viable is the poor long-term stability, particularly at high current densities. The rudimentary cause for the instability is believed to result from the mechanical delamination of oxygen electrode (OE) from the electrolyte due to the mismatch in oxygen evolution reaction (OER) rate and applied current density, which results in high oxygen partial pressure at the interface. Therefore, a way to minimize the delamination is to enhance OE’s OER rate (i.e. reduce OER area-specific-resistance, ASR) to match the high applied current density. In this presentation, we show the employment of three-electrode symmetrical cell method to exclusively characterize the OER’s ASR of bilayer OE under applied current density at high temperatures. The results explicitly show that the bilayer OE with low OER’s ASR outperforms the baseline single layer OE (LSCF-GDC) in long-term stability at high current density of 1 A/cm2 and 700oC; the former can last ~1000 hrs under a constant 1A/cm2 current before observing performance degradation and delamination, whereas the latter shows significant performance degradation and delamination even after 100 hrs. We conclude that the bilayer OE exhibits a better chemical, thermal, mechanical, and more importantly electrochemical stability over the benchmark single layer LSCG-GDC OE.