Engineering the Heterostructured\nNi<sub>9</sub>S<sub>8</sub>–FeO<sub><i>x</i></sub> Nanoarrays for Electrocatalytic\n(Sea)Water Splitting

Constructing transition metal multiphase composites can\nimprove\nthe electrocatalytic efficiency of (sea)water splitting via interfacial\ninteraction between adjacent active sites. Herein, the self-supporting\nNi<sub><i>m</i></sub>S<sub><i>n</i></sub>-FeO<sub><i>x</i></sub> heterostructure is in situ grown on nickel\nfoam (NF) through a corrosion engineering approach, which displays\nabundant dendritic array structures, endowing the material with abundant\nactive sites and high electrocatalytic active area. The control of\nintroducing Fe<sup>3+</sup> and sulfur precursors can effectively\ntrigger the phase transiting from Ni<sub>3</sub>S<sub>2</sub> to Ni<sub>9</sub>S<sub>8</sub>, generating more S vacancies, which could reduce\nthe reaction energy barrier and improve the electrocatalytic performance.\nSimultaneously, the presence of Fe–S bonding at the sulfide/oxide\ninterface brings a strong electronic interaction, which enables the\ntuning of the adsorption energy of the reaction intermediates and\naccelerates the catalytic reaction kinetics. As a result, the Ni<sub>9</sub>S<sub>8</sub>–FeO<sub><i>x</i></sub>/NF-Fe<sub>8.0</sub> catalyst presents low overpotentials of 159 mV and 190\nmV for oxygen evolution reaction at 100 mA cm<sup>–2</sup> under\n1 M KOH solution and simulated seawater conditions, respectively.\nThe overall water splitting incorporating the Ni<sub>9</sub>S<sub>8</sub>–FeO<sub><i>x</i></sub>/NF-Fe<sub>8.0</sub> as both anode and cathode provides the potential of 1.707 V in 1\nM KOH and 1.794 V in simulated seawater at 100 mA cm<sup>–2</sup>. This research furnishes an efficient strategy toward the design\nof advanced transition metal heterogeneous composites with strong\ninterfacial interaction for (sea)water splitting.