An Effective Strategy to Enhance the Electrocatalytic Activity of Ruddlesden−Popper Oxides Sr₃Fe₂O₇₋<i>_δ</i> Electrodes for Solid Oxide Fuel Cells

Abstract

The target of this work is to develop advanced electrode materials with excellent performance compared to conventional cathodes. Cobalt-free Ruddlesden−Popper oxides Sr3Fe2−xCuxO7−δ (SFCx, x = 0, 0.1, 0.2) were successfully synthesized and assessed as cathode materials for solid oxide fuel cells (SOFCs). Herein, a Cu-doping strategy is shown to increase the electrical conductivity and improve the electrochemical performance of the pristine Sr3Fe2O7−δ. Among all the cathode materials, the Sr3Fe1.9Cu0.1O7−δ (SFC10) cathode exhibits the best electrocatalytic activity for oxygen reduction reaction (ORR). The polarization resistance is 0.11 Ω cm2 and the peak power density of the single-cell with an SFC10 cathode reaches 955 mW cm−2 at 700 °C, a measurement comparable to cobalt-based electrodes. The excellent performance is owed to favorable oxygen surface exchange capabilities and larger oxygen vacancy concentrations at elevated temperatures. Moreover, the electrochemical impedance spectra and distribution of relaxation time results indicate that the charge transfer process at the triple-phase boundary is the rate-limiting step for ORR on the electrode. This work provides an effective strategy for designing novel cathode electrocatalysts for SOFCs.

Keywords

• solid oxide fuel cells
• cathode material
• Ruddlesden−Popper oxides
• electrochemical performance