Surface-Guided Formation of Amorphous Mixed-Metal Oxyhydroxides on Ultrathin MnO₂ Nanosheet Arrays for Efficient Electrocatalytic Oxygen Evolution

Earth-abundant amorphous nanomaterials with rich structural defects are promising alternative catalysts to noble metals for an efficient electrochemical oxygen evolution reaction; however, their inferior electrical conductivity and poor morphological control during synthesis hamper the full realization of their potency in electrocatalysis. Herein, a rapid surface-guided synthetic approach is proposed to introduce amorphous and mixed-metal oxyhydroxide overlayers on ultrathin Ni-doped MnO₂ (NiMnO₂) nanosheet arrays via a galvanic replacement mechanism. This method results in a monolithic 3D porous catalyst with a small overpotential of only 232 mV to achieve a current density of 10 mA cm⁻² in 1 m KOH, which is much lower than the corresponding value of 307 mV for the Ni-MnO₂ reference sample. Detailed structural and electrochemical characterization reveal that the unique NiMnO₂ ultrathin nanosheet arrays do not only provide a large surface area to guide the formation of active amorphous catalyst layers but also ensure the effective charge transport owing to their high electron conductivity, collectively contributing to the greatly improved catalyst activity. It is envisioned that this highly operable surface-guide synthetic strategy may open up new avenues for the design and fabrication of novel 3D nanoarchitectures integrated with functional amorphous materials for broadened ranges of applications.