Superior power density solid oxidefuel cells by enlarging the three-phase boundary region of a NiO–Ce0.8Gd0.2O1.9 composite anode through optimized surface structure

Abstract

In an effort to boost the power densities of solid oxide fuel cells (SOFCs) operating at intermediate temperatures (600–750 °C), novel powder synthesis methods have been studied with the goal of increasing the three-phase boundary region of the anode. Porous anodes composed of Ni and Ce_0.8Gd_0.2O_1.9 (GDC) cermet are commonly studied in SOFCs, but the cell performance is limited by their dependency on the three-phase boundaries at which the electrochemical oxidation reaction takes place. This paper presents a remarkable improvement in the electrochemical performance through a significant enlargement of the three-phase boundary region by an optimization of the surface structure. The strategy starts with the premise that the oxide powder particles in aqueous solution carry a positive or negative electrical charge depending upon the pH of the solution, and the charge can be exploited to attach chelated metal ions to their surface, extending the three-phase boundary region. This modified NiO–GDC composite powder resulted in not only an extension of both electronic and O²⁻ ionic conduction pathways, but also a suppression of grain growth in the anode during the process of cell fabrication. As the final outcome, the modified Ni–GDC anode-supported cells show far superior power densities (1.85 W cm⁻² at 750 °C and 0.83 W cm⁻² at 600 °C) in H₂ compared to the conventional Ni–GDC anode-supported cells (0.61 W cm⁻² at 750 °C and 0.26 W cm⁻² at 600 °C).