A niobium and tungsten co-doped SrFeO3- perovskite as cathode for intermediate temperature solid oxide fuel cells

Unveiling Lithium Roles in Cobalt‐Free Cathodes for Efficient Oxygen Reduction Reaction below 600 °C

“…The fitted peaks at~710.3 eV and~723.7 eV correspond to the Fe2p 3/2 and Fe2p 1/2 for Fe 3 + , respectively, which is confirmed by the characteristic shake-up at about 719.9 eV. [23,39] The peaks at~712.4 eV and~725.9 eV are assigned to Fe 4 + in the Fe2p 3/2 and Fe2p 1/2 regions, respectively. [23] When Li is introduced, the relative Fe content (vs. A-site cations such as Sr and/or Li) at the surface significantly drops from 43.7 % to 4.59-6.34 %.…”

“…This substantial size mismatch between Li and Sr decreases the free 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 energy (lattice strain, surface bond strength) of the surrounding lattice, which drives the in situ diffusion of Li + to the oxide surface, resulting in a partial A-site deficiency in the bulk. [23] When Li is introduced, the relative Fe content (vs. A-site cations such as Sr and/or Li) at the surface significantly drops from 43.7 % to 4.59-6.34 %. There predominately Fe 3 + and Fe 4 + species at the surface.…”

“…[36] The ionic radius of the dopant Li + (0.92 Å) is 0.638 times the ionic radii of host Sr 2 + (1.44 Å). [23,39] The peaks at~712.4 eV and~725.9 eV are assigned to Fe 4 + in the Fe2p 3/2 and Fe2p 1/2 regions, respectively. [37][38] The iron valence state at the surface of the Sr 1À x Li x Fe 0.8 Nb 0.1 Ta 0.1 O 3-δ (0 � x � 0.1) samples were determined by deconvoluting the high-resolution X-ray photoelectron spectroscopy (XPS) spectra of Fe2p regions, as shown in Figure 2.…”

“…[5] Cobalt-containing perovskite oxides such as SrCo 0.8 Nb 0.1 Ta 0.1 O 3-δ have attracted immense research interest as potential IT-SOFC cathodes because of their high mixed ionic and electronic conductivities (MIECs). [19][20][21][22][23] However, because of their lower MIECs SF-based cathodes normally exhibit a lower ORR activity than Co-based cathodes in the IT range. However, the high cost of cobalt, mismatched thermal expansion coefficients (TECs) with ceria-based electrolytes, and chemical incompatibility with zirconium-based electrolytes are the major concerns for the practical application of cobalt-containing perovskites in IT-SOFCs.…”

“…at the B-site (Fe-site). [19][20][21][22][23] However, because of their lower MIECs SF-based cathodes normally exhibit a lower ORR activity than Co-based cathodes in the IT range. [24][25] To circumvent these challenges, charge imbalance could be introduced at the A-site through incorporating lowvalent cations such as alkali metals.…”