Synthesis and electrocatalytic properties of La 0.8 Sr 0.2 FeO 3−δ perovskite oxide for oxygen reactions

Perovskites are important alternatives for precious metals as catalysts for bifunctional oxygen electrodes, involving oxygen evolution (OER) and reduction (ORR) reactions as is the case of regenerative fuel cells. In this work, strontium doped lanthanum ferrite La 1− x Sr x FeO 3− δ ( x = 0; 0.1; 0.2; 0.3; 0.4; 0.6 and 1.0) powders were prepared by a self-combustion route. The oxides, in the form of carbon paste electrodes, were characterised by cyclic voltammetry in alkaline solutions. Data analyses lead to the selection of La 0.8 Sr 0.2 FeO 3− δ to prepare gas diffusion electrodes (GDEs). Cyclic voltammetry and steady state polarization curves were used, respectively, to assess the electrochemical behaviour of GDEs and to obtain kinetic data for both OER and ORR. It is concluded that the oxide preparation conditions/electrode configuration determine the electrode performance. The bifunctionality of the electrodes was assessed, under galvanostatic control, using a cycling protocol within the potential domains for OER and ORR. The potential window, i.e., the total combined overpotential between OER and ORR was found to be of ≈770 mV, value which compares well with that obtained under potentiostatic control. Even though the potential window keeps constant during 140 cycles, the increase in cycling time and/or current density (≥2.5 mA·cm −2 ) led to a gradual metallization of the GDE surface, as confirmed by Scanning Electron Microscopy and X-ray diffraction analysis.