Metastable State Structure Promotes Surface Reconstruction of Spinel NiFe2O4 for Efficient Oxygen Evolution Reaction

The regulation of catalyst surface structure in catalytic process is the basis of regulating catalytic performance. For spinel materials, the common active phases on their surfaces in the oxygen evolution reaction (OER) are metal hydroxyl oxides, so promoting its surface reconstruction to form the metal hydroxyl oxide to improve the catalytic activity is one of the commonly used modification methods. In this work, amorphous P-doped NiFe2O4 (A-P-NFO) was successfully prepared by hydrothermal method and phosphating treatment. The amorphous structure can lead to a strong polarization effect in A-P-NFO, where electrons are attracted from the antibonding orbitals to the empty orbitals, thus lowering the average valence state of nickel and activating the Ni-O bond. Unlike other reported work on NFO, this work demonstrates that the lower Ni and Fe valence states are more favorable for catalytic activity. In addition, the amorphous structure keeps A-P-NFO in a metastable state, which will be conducive to the leaching of surface cations, accelerating the surface reconstruction of A-P-NFO during the OER process, and thus playing a key role in the improvement of the catalytic performance of OER. The synchrotron radiation, in-situ Raman spectra and DFT calculations demonstrate that the A-P-NFO is conducive to electron transfer and adsorption of electroactive species (OH*, O*, etc.) for OER. TheA-P-NFOexhibits the excellent OER catalytic performance under alkaline electrolyte conditions, achieving a low overpotential of 240 mV at 10 mA cm-2 and maintaining high catalytic stability over 48 h. Furthermore, its OER catalytic performance is superior to the recently reported catalysts of the similar type. The method of turning the catalyst into metastable state structure through P doping and amorphization strategy is expected to provide new research ideas and application prospects for improving the catalytic performance of similar catalysts.