Remarkably enhanced water splitting activity of nickel foam due to simple immersion in a ferric nitrate solution

The development of a facile method to construct a high-performance electrode is of paramount importance to the application of alkaline water electrolysis. Here, we report that the activity of nickel foam (NF) towards the oxygen evolution reaction (OER) can be enhanced remarkably through simple immersion in a ferric nitrate (Fe(NO₃)₃) solution at room temperature. During this immersion process, the oxidation of the NF surface by NO₃^- ions increases the near-surface concentrations of OH^- and Ni²⁺, which results in the in situ deposition of a highly active amorphous Ni-Fe hydroxide (a-NiFeO_xH_y) layer. Specifically, the OER overpotential of the NF electrode decreases from 371 mV (bare NF) to 270 mV (@10 mA·cm^-2 in 0.1 M KOH) after immersion in a 20 mM Fe(NO₃)₃ solution for just 1 min. A longer immersion time results in further increased OER activity (196 mV@10 mA·cm^-2 in 1 M KOH). The overall water splitting properties of the a-NiFeO_xH_y@NF electrode were evaluated using a two-electrode configuration. It is worth noting that the current density can reach 25 mA·cm^-2 in 6 M KOH at an applied voltage of 1.5 V at room temperature.