Deeply reconstructed hierarchical and defective NiOOH/FeOOH nanoboxes with accelerated kinetics for the oxygen evolution reaction

Abstract

Transition metal phosphides (TMPs) have been reported as efficient pre-catalysts for the oxygen evolution reaction (OER) in alkaline media. In situ generated metal oxyhydroxides on the surface of TMPs serve as real active sites. However, the reconstruction of most of the reported TMPs is incomplete and the active components cannot be fully used. Herein, hollow nanostructured Ni₅P₂/FeP₄ nanoboxes (NiFeP NBs) are designed and synthesized as pre-catalysts. During the OER, the NiFeP NBs deeply reconstruct into low-crystalline and ultrathin NiOOH/FeOOH nanosheet assembled nanoboxes (NiOOH/FeOOH NBs). In situ Raman spectroscopy and ex situ characterization studies provide evidence that the hollow nanostructure facilitates the deep reconstruction of NiFeP NBs. Benefiting from the hierarchical hollow structure, the abundant interface between NiOOH and FeOOH, and plentiful defects, the reconstructed NiOOH/FeOOH NBs exhibit superior OER activity and excellent stability. Density functional theory (DFT) calculations reveal that the Fe–Ni dual sites in the NiOOH/FeOOH interface may be the possible active sites.