EFFECT OF THE CALCINATION TEMPERATURE ON THE OXYGEN EVOLUTION REACTION OVER Pr6O11 OXIDE

Abstract

The Pr₆O₁₁ oxide synthesized using the citrate sol-gel method was calcined at four temperatures 600, 700, 800 and 900 °C. The prepared powder was characterized by DTA-TGA, XRD, IR and SEM. The thermal analysis shows an endothermic peak at 765°C attributed the pure cubic phase.  XRD diffraction pattern reveal that three phases Pr₂CO₅, Pr₄O₇ and Pr₆O₁₁ coexist at 600°C. At T ≥ 700°C, secondary phases Pr₂CO₅, Pr₄O₇ disappear while the phase Pr₆O₁₁ becomes alone indicating the formation of the pure cubic phase. IR spectra show two bandes at ~ 580 and 660 cm^-1 assigned to Pr-O bonds confirming the formation of the Pr₆O₁₁ cubic structure. The microstructural analysis shows that powders are constituted from particles having different shape, size and are agglomerated.  The electrocatalytic properties of samples were investigated using cyclic voltammetry, Tafel slopes, electrochemical impedance spectroscopy. The activity for the oxygen evolution reaction decreases with increasing the calcination temperature. The obtained Tafel slopes are 59, 71 and 85 mV.dec^-1 for the Pr₆O₁₁ oxide calcined at 700, 800 and 900°C respectively.