Solid oxide cells with cermet of silver and gadolinium-doped-ceria symmetrical electrodes for high-performance power generation and water electrolysis

Abstract

A cermet of silver and gadolinium-doped-ceria (Ag-GDC) is investigated as novel symmetrical electrode material for (ZrO2)0.92(Y2O3)0.08 (YSZ) electrolyte-supported solid oxide cells (SOCs) operated in fuel cell (SOFC) and electrolysis (SOEC) modes. The electrochemical performances are evaluated by measuring the current density-voltage characteristics and impedance spectra of the SOCs. The activity of hydrogen and air electrodes is investigated by recording overpotential versus current density in symmetrical electrode cells, respectively in hydrogen and air, using a three-electrode method. Conventional hydrogen electrode, Ni-YSZ, and oxygen electrode, LSCF (La0.6Sr0.4Co0.2Fe0.8O3-δ)-GDC, are tested as comparison. The results show that, as an oxygen electrode, Ag-GDC is more active than LSCF-GDC in catalyzing both oxygen reduction reaction (ORR) in an SOFC and oxygen evolution reaction (OER) in an SOEC. As a hydrogen electrode, Ag-GDC is more active than Ni-YSZ in catalyzing hydrogen oxidation reaction (HOR) in an SOFC and hydrogen evolution reaction (HER) in an SOEC, especially in high steam concentration. An SOC with symmetrical Ag-GDC electrodes operated in a fuel cell mode, with 3% H2O humidified H2 as the fuel, displays a peak power density of 395 mWcm−2 at 800 °C. Its polarization resistance at open circuit voltage is 0.21 Ω cm2. Ag-GDC electrode can be operated even at pure steam. An SOEC operated for electrolyzing 100% H2O, the current density reaches 720 mA cm−2 under 1.3 V at 800 °C.