Rational Design of a Metallic Functional Layer for High-Performance Solid Oxide Fuel Cells

The rational design of the electrode–electrolyte interface plays a crucial role in expediting the oxygen reduction reaction (ORR) kinetics of intermediate-temperature solid oxide fuel cells (IT-SOFCs). We employed metallic functional layers because of their high electrical conductivities and catalytic activities with respect to ORR kinetics. Using electrohydrodynamic (EHD) jet printing, we printed a metallic grid structure at the interface of Sm0.5Sr0.5CoO3−δ (SSC) and Gd0.1Ce0.9O2−δ (GDC) with Al, Ni, and Ag to systematically quantify the effects of the electrical conductivity and catalytic activity on ORR kinetics. Substantial improvements in interfacial properties were achieved with the metallic functional layers, manifested by reducing the polarization resistance to 12.5% of the bare SSC cathode. I–V characterization, electrochemical impedance spectroscopy (EIS) measurements, and distributed relaxation times (DRT) based on impedance fitting enabled the quantitative deconvolution and revealed that the enhanced electrical conductivity of the metallic functional layer was primarily responsible for the increased electrochemical performance compared to the enhanced catalytic activity. The SSC cathode with the Ag functional layer exhibited the highest peak power density of ∼670 mW/cm2 at 650 °C, which was higher than that of the bare SSC cathode by ∼1.8 times.