Exsolution and electrochemistry in perovskite solid oxide fuel cell anodes: Role of stoichiometry in Sr(Ti,Fe,Ni)O3

MOGNI, LILIANA V.; BARNETT, SCOTT A.; TROIANI, HORACIO; HAN, MINFANG; ZHU, TENGLONG; SANTAYA, MARIANO

JOURNAL OF POWER SOURCES

ELSEVIER SCIENCE BV

Año: 2019 vol. 439

0378-7753

The exsolution of metal cations from oxides under reducing fuel conditions results in the formation of surfacemetallic nanoparticles, which can reduce Solid Oxide Fuel Cell anode polarization resistance. However, the lossof the B-site cations shifts the stoichiometry of the perovskite oxide. Depending on the amount exsolved and theinitial stoichiometry, the exsolution can presumably shift the oxide away from its single-phase perovskite region.Herein, the direct comparison of initially stoichiometric composition Sr(Ti0.3Fe0.63Ni0.07)O3-δ (STFN0) withinitially A-site deficient Sr0.95(Ti0.3Fe0.63Ni0.07)O3-δ (STFN5) is conducted and reported. X-ray diffraction alongwith scanning and transmission electron microscopy analysis of the oxides, which are both reduced at 850 �C inH2/H2O/Ar, shows a similar size and density of exsolved Fe?Ni alloy nanoparticles, albeit with slightly differentalloy compositions. Whereas the oxide phase in reduced STFN5 shows a well-ordered perovskite structure, thegreater B-site deficiency in reduced STFN0 results in a highly disordered and strained structure. The electrochemicalperformance of STFN0 anodes is inferior to that of STFN5 anodes, and even worse than SrTi0.3Fe0.7O3-δ(Ni-free) anodes. It appears that an initial Sr deficiency is important to avoid a too-high B-site deficiency afterexsolution, which distorts the perovskite structure and impairs electrochemical processes.