Redox Cycling of Ni/YSZ and Ni/GDC Anodes for Metal-Supported Fuel Cells

Abstract

Metal-supported fuel cells (MSCs) are promising candidates for non-stationary applications like auxiliary power units or range extenders in battery electric vehicles. They are attractive due to their potential to withstand fast thermal cycles and vibrations during cell operation. In addition, they have to withstand redox cycles, which might occur during start-up and shut-down of the fuel cell stack. Recently, a novel nickel/gadolinium doped ceria anode (Ni/GDC) was introduced in the metal-supported fuel cell concept of Plansee SE which almost tripled current density compared to the standard cell concept with a Ni/YSZ anode. In the present work, both cell concepts were compared regarding their ability to withstand harsh redox cycles. Therefore, after initial check at 750 °C, cell performance of button cells after controlled redox cycles was investigated at different temperature steps respectively. Re-oxidation temperature of the anodes was varied between 300 and 700 °C for 10 min in air. Afterwards, reduction of the anode was conducted by purging anode side with N2 for 10 min and then going back to standard cell operation conditions with H2 supply. The response of cell performance on redox cycling was recorded continuously. While standard MSCs with Ni/YSZ anode showed a strong degradation after a few cycles if the oxidation was conducted at temperatures above 600 °C, novel MSCs with Ni/GDC anode showed a remarkable resistance against re-oxidation. For a deeper understanding of this behavior, microstructural investigation of the Ni/GDC anode and the adjacent electrolyte was performed within the tested cells by FE-SEM and FIB-SEM 3D structure analysis. Furthermore, electrochemical behavior of Ni/GDC anode was investigated at a larger cycle number of up to 50 redox cycles with 2 h air supply each