Valence regulation of ferrite perovskite for high performance cobalt‐free cathode of solid oxide fuel cell

Abstract

The development of a cobalt-free cathode with long-term stability and high electrochemical activity is important for constructing low-cost and robust solid oxide fuel cells (SOFCs). Here, we report performance enhancement of a cobalt-free cathode achieved by valence regulation of the ferrite-based perovskite. Utilizing co-doping of high valence niobium with low valence nickel, we developed a cathode material La 0.8 Sr 0.2 Fe 0.8 Ni 0.15 Nb 0.05 O 3Àδ that allowed representing adequate conductivity of 214 S cm À1 at 700 C, decent thermal compatibility with thermal expansion coefficient being 12 Â 10 À6 K À1 , superior electrochemical properties manifested by area-specific resistance of 0.06 Ω cm 2 and peak power density of 760 mW cm À2 at 800 C, and excellent discharge durability of over 480 h at a current density of 460 mA cm À2 under 750 C. This significantly enhanced performance originates from a proper regulation of the electronic structure rendered by synergistic effects induced by the co-doping of the high valence niobium with low valence nickel into the B sites of the ferrite perovskite. Such a regulation enables an optimized compromise among the oxygen vacancies, electronic mobility, oxygen adsorption and dissociation, and strontium segregation.

Segregation and interdiffusion processes in perovskites: a review of recent advances

“…The introduction of nickel and/or niobium has a favourable effect on the stability of La 0.8 Sr 0.2 Fe 0.8− x − y Ni x Nb y O 3− δ oxides, since it suppresses the surface segregation of strontium. 140 The Sr surf /Sr lat ratio by XPS analysis in LSF, LSFNb and LSFNNb changed from 1.58, 1.35, 0.91 and 0.78 to 1.53, 1.38, 0.67 and 0.60, respectively, after long-term operation, indicating material stability. Chromium doping of (La 0.8 Sr 0.2 ) 0.95 Fe 0.5 Cr 0.5 O 3− δ oxide does not reduce the segregation processes; 143 the deposition process takes place at the ceramic grain boundaries.…”