| Summary: | Perovskites of strontium cobalt oxyhalides having the chemical formulae Sr<sub>2</sub>CoO<sub>4-x</sub>H<sub>x</sub> (H = F, Cl, and Br; x = 0 and 1) were prepared using a solid-phase synthesis approach and comparatively evaluated as electrocatalysts for oxygen evolution in an alkaline solution. The perovskite electrocatalyst crystal phase, surface morphology, and composition were examined by X-ray diffraction, a scanning electron microscope, and energy-dispersive X-ray (EDX) mapping. The electrochemical investigations of the oxyhalides catalysts showed that the doping of F, Cl, or Br into the Sr<sub>2</sub>CoO<sub>4</sub> parent oxide enhances the electrocatalytic activity for the oxygen evolution reaction (OER) with the onset potential as well as the potential required to achieve a current density of 10 mA/cm<sup>2</sup> shifting to lower potential values in the order of Sr<sub>2</sub>CoO<sub>4</sub> (1.64, 1.73) > Sr<sub>2</sub>CoO<sub>3</sub>Br (1.61, 1.65) > Sr<sub>2</sub>CoO<sub>3</sub>Cl (1.53, 1.60) > Sr<sub>2</sub>CoO<sub>3</sub>F (1.50, 1.56) V vs. HRE which indicates that Sr<sub>2</sub>CoO<sub>3</sub>F is the most active electrode among the studied catalysts under static and steady-state conditions. Moreover, Sr<sub>2</sub>CoO<sub>3</sub>F demonstrates long-term stability and remarkably less charge transfer resistance (R<sub>ct</sub> = 36.8 ohm) than the other oxyhalide counterparts during the OER. The doping of the perovskites with halide ions particularly the fluoride-ion enhances the surface oxygen vacancy density due to electron withdrawal away from the Co-atom which improves the ionic and electronic conductivity as well as the electrochemical activity of the oxygen evolution in alkaline solution.
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