High and durable performance of an external-manifold designed reversible solid oxide cell stack

Abstract

A 5-cell reversible solid oxide cell stack in external-manifold design is fabricated with planar cells with an active area of 169 cm2, Ni–Y2O3 stabilized ZrO2 (Ni-YSZ) support, Ni-YSZ functional anode (fuel electrode), YSZ electrolyte, and YSZ-composite cathode (air electrode). It is operated at various temperatures in different atmospheres. In fuel cell mode at 750 °C with H2 fuel and air oxidant, the stack generates 407 W (481.7 mW cm−2, 81.4 W per cell) at 0.68 A cm−2. In electrolysis mode, with H2-55% H2O at 750 °C, the current density at the thermo-neutral voltage (6.45 V) is −0.340 A cm−2, and concentration polarization starts at around −0.3 A cm−2. They are −0.592 A cm−2 and above −0.50 A cm−2, respectively, under 80% H2O and 800 °C. H2 production rate increases from 88 NL h−1 to 209 NL h−1, accordingly. Using H2-80% H2O for fuel electrode at 800 °C, the stack performs at around 7.0 V and −0.5 A cm−2 for up to 900 h without gas leaking and cell delamination and with more severe metal oxidation at the spots where the SUS430 interconnect contacts with Ni foam current collector on the fuel electrode side.