In situ unraveling surface reconstruction of Ni5P4@FeP nanosheet array for superior alkaline oxygen evolution reaction

Oxygen evolution reaction (OER) is a key step for electrochemical water splitting and understanding the surface reconstruction of OER pre-catalysts is of vital importance. Herein, hybrid Ni5P4 @FeP nanosheet arrays were evaluated as promising OER pre-catalysts. The dynamic surface evolution was probed by in situ Raman spectroscopy, which revealed that Ni5P4 @FeP was rapidly reconstructed to NiFe2O4 during the anodic scan. The structural instability of amorphous NiFe2O4 led to partial reconstitution to Ni/FeOOH at high oxidation potentials. As-formed Ni/FeOOH@NiFe2O4 hybrid with high structural reversibility was established as a truly active species, which exhibited excellent alkaline OER performance with a low overpotential of 205 and 242 mV under current densities of 10 and 100 mA cm−2, respectively. This work provides a facile strategy to in situ construct an amorphous spinel/oxyhydroxide hybrid structure using electrochemical activation that holds strong promise for potential application in electrochemical water splitting and related energy devices. [Display omitted] •Surface reconstruction of Ni5P4@FeP was probed by in situ Raman spectroscopy.•Ni5P4@FeP was oxidized to NiFe2O4 and further to Ni/FeOOH at high potentials.•The real active intermediate was identified as Ni/FeOOH and NiFe2O4 hybrid.•High structural reversibility between NiFe2O4 and Ni/FeOOH was found.•As-formed amorphous NiOOH and NiFe2O4 hybrid showed superior OER activity.