Optimisation of high-performance, cobalt-free SrFe1-xMoxO3-y cathodes for solid oxide fuel cells prepared by spray pyrolysis

Abstract

Strontium-ferrite-based perovskites as cobalt-free cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs) have been analysed employing structural, stability and electrochemical studies. Neutron diffraction of SrFeO3-δ and SrFe0.9Mo0.1O3-δ prepared by a Pechini method confirmed that SrFeO3-δ undergoes a phase transition from tetragonal to cubic symmetry at 300–400 °C, whereas Mo-doping stabilises cubic symmetry in the range RT-900 °C. Spray-pyrolysed electrodes offered significantly lower area-specific resistances of 0.2 and 0.11 Ω cm2 for SrFeO3-δ and SrFe0.9Mo0.1O3-δ at 700 °C, respectively, in comparison to their analogues synthesised by the Pechini method (0.55 and 0.42 Ω cm2), and lower grain size, as confirmed by scanning electron microscopy. Thermal cycling and ageing studies indicated a more robust response for the spray-pyrolysed electrodes, in particular the Mo-doped phase, which achieved a stable electrode-polarisation resistance <0.1 Ω cm2 for 10 heating/cooling cycles and 100 h of ageing at 700 °C. Anode-supported single cells with a thin Ce0.9Gd0.1O2-δ electrolyte produced performances of 0.5 and 0.9 W cm−2 at 700 and 800 °C, respectively. SrFe0.9Mo0.1O3-δ deposited by spray pyrolysis is, thus, proposed as a promising cobalt-free cathode for IT-SOFC based on its good structural stability and highly competitive electrochemical performance