Self-Supported Stainless Steel Nanocone Array Coated with a Layer of Ni-Fe Oxides/(Oxy)hydroxides as a Highly Active...

Highly efficient, robust, and cheap water oxidation electrodes are of great significance for large-scale production of hydrogen by electrolysis of water. Here, a self-supported stainless steel (SS) nanocone array coated with a layer of nanoparticulate Ni-Fe oxides/(oxy)hydroxides was fabricated by a facile, low-cost, and easily scalable two-step process. The construction of a nanocone array on the surface of an AISI 304 SS plate by acid corrosion greatly enlarged the specific surface area of the substrate, and the subsequent formation of a layer of Ni-Fe oxides/(oxy)hydroxides featuring the NiFe₂O₄ spinel phase on the nanocone surface by electrodeposition of [Ni(bpy)₃]²⁺ significantly enhanced the intrinsic activity and the stability of the SS-based electrode. The as-prepared electrode demonstrated superior activity for the oxygen evolution reaction (OER) in 1 M KOH, with 232 and 280 mV overpotentials to achieve 10 and 100 mA cm_geo^-2 current densities, respectively. The high activity of the electrode was maintained over 340 h of chronopotentiometric test at 20 mA cm_geo^-2, and the electrode also showed good stability over 100 h of electrolysis at high current density (200 mA cm^-2). More important for practical application, the used SS-based electrode can be easily regenerated with the original OER activity. The superior activity of this SS-based electrode stems from synergistic combination of high conductivity of the SS substrate, a large electrochemically active surface area of the nanocone array, and a uniformly coated nanoparticulate Ni-Fe oxide/(oxy)hydroxide layer with an optimal Ni/Fe ratio.