Ultralow Loading of Ru as a Bifunctional Catalyst for the Oxygen Electrode of Solid Oxide Cells

The oxygen evolution reaction (OER) is a significant contributor to the cell overpotential in solid oxide electrolyzer cells (SOECs). Although noble metals such as Ru and Ir have been utilized as OER catalysts, their widespread application in SOECs is hindered by their high cost and limited availability. In this study, we present a highly effective approach to enhance air electrode performance and durability by depositing an ultrathin layer of metallic Ru, as thin as ∼7.5 Å, onto (La_0.6Sr_0.4)_0.95Co_0.2Fe_0.8O_3-δ (LSCF) using plasma-enhanced atomic layer deposition (PEALD). Our study suggests that the emergence of a perovskite, SrRuO₃, resulting from the reaction between PEALD-based Ru and surface-segregated Sr species, plays a crucial role in suppressing Sr segregation and maintaining favorable oxygen desorption kinetics, which ultimately improves the OER durability. Further, the PEALD Ru coating on LSCF also reduces the resistance to the oxygen reduction reaction (ORR), highlighting the bifunctional electrocatalytic activities for reversible fuel cells. When the LSCF electrode of a test cell is decorated with ∼7.5 Å of the Ru overcoat, a current density of 656 mA cm^-2 at 1.3 V in electrolysis mode and a peak power density of 803 mW cm^-2 in fuel cell mode are demonstrated at 700 °C, corresponding to an enhancement of 49.1 and 31.9%, respectively, compared to the pristine cell.