Selenization triggers deep reconstruction to produce ultrathin γ-NiOOH toward the efficient water oxidation

Transition metal chalcogenides will be in situ transformed into metal oxyhydroxides during oxygen evolution reaction (OER) process in alkaline medium. However, most of these compounds only undergo surface reconstruction under operating conditions, which contains a large percentage of inactive atoms in the core, thus limiting the exposure of the active sites. Here, we synthesize a Ni-Mo-Se precatalyst with three-dimensional hierarchical structure and develop a facile on-site electrochemical activation strategy for achieving deep reconstruction of the precatalyst. Using the combination of multiple spectroscopic characterizations and high resolution electron microscopy techniques, we unravel that the Ni-Mo-Se precatalyst is deeply reconstructed into γ-NiOOH with co-leaching of Mo and Se after the anodic oxidation. Such flower-like γ-NiOOH is constituted by distorted ultrathin nanosheets with a thickness of ∼ 4.5 nm and contains abundant intercalated species such as water and OH–/CO32–, thus offering a large quantity of accessible active sites. To reach the current density of 10 mA cm−2, the derived electrode requires an overpotential of only 244 mV, outperforming almost all the reported analogues. This work highlights the reconstruction chemistry and provides a simple method for the preparation of efficient OER electrocatalyst.