Defective Sr0.9Mo0.9O3−δ perovskites with exsolved Ni nanoparticles as high-performance composite anodes for solid-oxide fuel cells

Abstract

An A-site deficient perovskite with metallic Ni in exsolution, Ni–Sr_0.9Mo_0.9O_3−δ, has been prepared, characterized and tested as an anode material in intermediate-temperature solid-oxide fuel cells (IT-SOFCs). It was obtained by reduction of a Ni-containing scheelite oxide, from which Ni is segregated to the surface as metal nanoparticles with average size of 30–35 nm, as demonstrated by high-resolution transmission electron microscopy (HR-TEM). An in situ neutron powder diffraction (NPD) study of the Sr_0.9Mo_0.9O_3−δ matrix shows an oxygen deficient cubic perovskite, defined in the Pmm space group; no crystalline transitions were detected in the tested temperature range up to 850 °C. Morphological observations using a scanning electron microscope (SEM) and pore size determinations by Hg porosimetry showed a highly porous material with macropores. The electrical conductivity gave a maximum value of 215 S cm⁻¹ at 850 °C. A suitable thermal expansion coefficient, with values close to that of the electrolyte, showed no abrupt changes in its slope. Polarization curves and electrochemical impedance spectra (EIS) under open circuit were investigated. In single-cell tests, the materials generated outstanding output powers close to 1025 mW cm⁻² at 850 °C using pure H₂ as fuel. All these features make this novel A-deficient perovskite with exsolved Ni particles a perfect candidate as anode material in intermediate-temperature SOFCs (IT-SOFCs).