In Situ Synthesis of Core–Shell-Ni₃Fe(OH)₉/Ni₃Fe 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 Ni3Fe nanosheet-framework and a thin layer of Ni3Fe(OH)9 shell on various substrates. The Ni3Fe alloy nanostructured framework provides large electroactive surface area and accelerates the charge transport, while the Ni3Fe(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 (ηonset = 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.