Stable Water Oxidation Catalysts Based on in-situ Electrochemical Transition of Nickel Phosphate

β-Ni(OH) 2 has been synthesized using Ni 3 (PO 4 ) 2 nanowires as precursors by in-situ electrochemical method. X-ray diffraction and selected area electron diffraction displayed that as-prepared Ni 3 (PO 4 ) 2 nanowires were transformed into β-Ni(OH) 2 with superlattice structure after activation. It has been found that extremely small size is crucial for the complete conversion of Ni 3 (PO 4 ) 2 and the formation of the superlattice structure. The resulting catalysts by in-situ conversion showed high activity and stability toward oxygen evolution reaction (OER) with an overpotential of 310 mV to reach the current density of 10 mA cm −2 and a long-term stability of 110 h. The large amount of NiOOH in the superlattice structure not only increases the OER activity of β-Ni(OH) 2 , but also improves the oxidation potential of nickel, thereby decreasing the dissolution. This work proves the feasibility of in-situ electrochemical synthesis for high-performance and stable hydroxide catalysts towards OER. Graphic Abstract