Dynamical changes of a Ni-Fe oxide water splitting catalyst investigated at different pH

By G
Published in Catalysis Today NULL 2016

Abstract

Abstract Mixed Ni-Fe oxide electrocatalysts have shown high catalytic activity for the oxygen evolution reaction (OER) in alkaline electrolyte. Fundamental research on mixed Ni-Fe {OER} catalysts has largely focused on high pH, while the {OER} activity near neutral pH has remained poorly studied. Here we review the activity of an amorphous mixed Ni-Fe oxyhydroxide catalyst supported on carbon (NiFeOx/C) in 0.1 M {KOH} pH 13, in 0.1 M borate buffer (Bi) pH 9.2, and in 0.1 M phosphate buffer (Pi) pH 7.0. The {OER} catalytic performance was found to decrease in the order of pH 13 pH 9.2 pH 7. In contrast to pH 13 and 9.2, the catalyst cycled in pH 7 showed an instantaneous decrease in {OER} activity and a simultaneous loss of the Ni(OH)2/NiOOH redox peak. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) showed the formation of crystalline areas upon {CV} cycling, which appeared more Ni enriched after cycling in pH 7. Deactivated electrodes cycled in pH 13 recovered the {OER} activity along with a partial reappearance of the Ni redox peak when subsequently cycled in pH 13. SEM-EDX spectroscopy confirmed compositional changes in the bulk during cycling at different pH, with an extensive leaching of Ni in pH 7. Our study provides new insight into the {OER} activity upon exposure to different electrolyte conditions, which unveils a highly dynamic Ni-Fe oxide framework.

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