An Effective Strategy to Enhance the Electrocatalytic Activity of Ruddlesden−Popper Oxides Sr3Fe2O7−δ 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.

High-Performance Sr0.95Fe0.8Mo0.1Ni0.1O3−δ Electrode for Reversible Symmetrical Solid Oxide Cells

“…The cial polarization resistances (Rp) of SFM-SDC/LSGM/SFM-SDC at 700, 750, 800, °C were 0.92, 0.55, 0.35, and 0.23 Ω cm 2 in air, respectively, and 1.82, 0.80, 0.43, and cm 2 in wet H2 (Figure 4a,b), respectively. Noticeably, the SFMN-SDC/LSGM/SFM symmetrical cells exhibited lower Rp values of 0.55, 0.28, 0.15, and 0.07 Ω cm 2 in spectively, and 0.58, 0.35, 0.22, and 0.11 Ω cm 2 in wet H2 at the above-mentioned atures (Figure 4c,d), respectively, suggesting the great promise of Sr0.95Fe0.8Mo0.1 as an electro-catalyst for SOC applications [2,10,44,45]. According to the i-V-P curves in the SOFC mode, when feeding 3% H2O-hum H2 to the anode and static ambient air to the cathode, both SFM-SDC/LSGM/SF and SFMN-SDC/LSGM/SFMN-SDC single cells presented open-circuit voltage (O ues above 1.0 V at 700-850 °C (Figure 5a,b).…”

“…Solid oxide cells (SOCs) can be used as solid oxide fuel cells (SOFCs) for the highly efficient and clean production of power from H 2 [8,9]. In addition, in the solid oxide electrolysis cell (SOEC) mode, H 2 O molecules can be split into H 2 and O 2− on a cathode catalyst, while O 2− migrates through the dense electrolyte to the anode to form O 2 [10][11][12]. Therefore, the use of SOCs as a highly possible strategy to realize power grid regulation has drawn much attention because of their highly efficient hydrogen conversion at high temperatures (600-1000 • C) [11][12][13].…”

“…However, Co-based electrodes have the intrinsic shortcoming of high thermal expansion coefficients (TECs) and poor stability and phase transitions, which result in ordered and disordered oxygen vacancies during high-temperature treatment [9,12,20]. With its good mixed conductivity and thermal dynamic stability, Fe-based perovskite ceramic SrFeO 3 has gained much attention as an electrode for RS-SOCs [8,10,24]. Doping higher valence cations at the B-site is a prospective method to lower the oxygen loss as well as alleviate lattice expansion [11,22,25].…”