Improved stability of reversible solid oxide cells with a nickelate-based oxygen electrode

The stability and performance of YSZ (yttria stabilized zirconia) based solid oxide cells with Ruddlesden–Popper phases as the oxygen electrode have significantly improved. Microtubular Solid Oxide Fuel Cells (mT-SOFCs) using Pr2NiO4+δ (PNO) as the oxygen electrode along with different electrolyte–electrode interlayers were fabricated and characterized in both fuel cell (FC) and electrolysis (SOEC) operation modes. The stability and performance of the cells strongly depend on the barrier layer used. In the FC mode, cells with the PNO–Ce0.9Gd0.1O2−δ (CGO) composite barrier layers showed power densities of ca. 0.63 W cm−2 at 800 °C and 0.7 V. In addition, they presented excellent stability as no degradation was observed after 100 hours under the operating conditions. Their performance in the electrolysis mode is also remarkable (−0.78 A cm−2 at 800 °C and 1.3 V). As anticipated, nickelates withstand the excess of oxygen at the electrode–electrolyte interface better than other oxygen electrode materials. Oscillatory current behaviour has been observed and ascribed to the partial decomposition reaction of the Pr2NiO4+δ phase into PrNiO3 and PrO2−y which, on the other hand, seems not to deteriorate the electrochemical properties of the cell. However, the PNO–CGO in situ reaction, forming mixed praseodymium, cerium and gadolinium oxides (PCGO) at the electrolyte–oxygen electrode interface, appears to be essential for the good stability and performance of the cells. In this study we demonstrate, for the first time, the excellent reversible SOFC/SOEC performance and stability under current load of a cell with nickelate based oxygen electrodes.