In Situ Synthesis of Core-Shell-Ni ₃ Fe(OH) ₉ /Ni ₃ Fe Hybrid Nanostructures as Highly Active and Stable Bifunctional Catalysts for Water Electrolysis

Development of cost-effective, high-performance electrocatalysts for water splitting is the key technological requirement for the hydrogen economy. Here, we report an in situ transformation approach for the preparation of a core-shell structured bifunctional electrocatalyst composed of a metallic Ni ₃ Fe nanosheet-framework and a thin layer of Ni ₃ Fe(OH) ₉ shell on various substrates. The Ni ₃ Fe alloy nanostructured framework provides large electroactive surface area and accelerates the charge transport, while the Ni ₃ Fe(OH) ₉ nanoshell allows an excellent electrochemical accessibility and high catalytic activity. When acting as an anode for the oxygen evolution reaction (OER), the hybrid catalyst is characterized by a low onset potential (η _onset = 230 mV), small Tafel slope (28 mV/dec), and stable catalytic activity (over 24 h). More importantly, the hybrid can act as an excellent bifunctional catalyst and deliver a current density of 10 mA cm ^-2 at a cell voltage of 1.63 V with long stability in a symmetric alkaline electrolyzer for overall water electrolysis.