The Effect of Ni Doping on the Performance and Electronic Structure of LSCF Cathodes Used for IT-SOFCs

Abstract

We investigated the effect of nickel doping on the electronic structure and performance of nanostructured La0.6­Sr0.4­Co0.2­Fe0.8–0.03­Ni0.03­O3−δ prepared by the one-pot sol–gel method. The commercial undoped La0.6­Sr0.4­Co0.2­Fe0.8­O3−δ (LSCF0.8) was used as reference. Moreover, for comparison, Ni (3 mol %) was deposited by wetness impregnation over the La0.6­Sr0.4­Co0.2­Fe0.8­O3−δ. We show by in situ X-ray absorption spectroscopy at 900 °C under air flow that nickel enters the B perovskite site of the material and favors the stabilization of the cobalt oxidation state, as evidenced by the delay in the decrease of the average Co valence with respect to undoped samples. Our results are further supported by in situ X-ray Raman spectroscopy (XRS) that allowed us to monitor the temperature evolution of the O K-edge. XRS evidences that nickel-doped LSCF shows unmodified O2p-TM3d density of states, which proves that the Co oxidation state is preserved. Electrochemical impedance spectroscopy measurements were carried out over half-cell systems consisting of LSCF-based materials deposited onto a Ce0.8­Gd0.2­O2−δ electrolyte. The improvement of the electrochemical performances of the Ni-doped La0.6­Sr0.4­Co0.2­Fe0.8–0.03­Ni0.03­O3−δ sample with respect to a reference Ni-impregnated LSCF is attributed to the stabilization of the TM-O6 structural units, which were recently proposed as the functional units for oxygen reduction.

A first-principles study on divergent reactions of using a Sr3Fe2O7 cathode in both oxygen ion conducting and proton conducting solid oxide fuel cells

“…32,33 Moreover, to get good compare with SrO-1 terminal surface (most stable surface) in Sr 3 Fe 2 O 7 , LaSrO (001) terminal surface of LSCF is adopted for catalytic activity investigation. 37,38 LSCF (001) surface has a surface energy of 1.15 eV, higher than those of SFO (001) surface, as shown in Table 1. Importantly, E vac and E hyrd on this surface are 2.66 and 3.59 eV, respectively, much higher than those of SFO, indicating that these defects are harder to generate in LSCF than in SFO.…”

In situ and operando characterisation techniques for solid oxide electrochemical cells: recent advances

“…In other cases measurements on the same samples are carried out on different beamlines following similar in situ treatments, as in the case of the study of Ni doped La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) cathodes as a function of temperature (up to 950 °C) [25]. The authors combined XAS (X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS)) measurements at the Fe, Co, and Ni K-edges with X-ray Raman scattering (XRS) measurements at the O K-edge at two different beamlines.…”

Novel cobalt and strontium-free perovskite Pr0.5Ba0.5Fe1-xNixO3-δ (x=0 and 0.2) as cathode for intermediate-temperature solid oxide fuel cells

“…2 N i 0 . 1 O 3 -δ [ 1 4 ] a n d La 0.6 Sr 0.4 Co 0.2 Fe 0.8 Ni 0.03 O 3-δ [15]. Consequently, B-site Fe-Ni combination is a good choice for electrode materials.…”