Engineering the Heterostructured Ni₉S₈–FeO_<i>x</i> Nanoarrays for Electrocatalytic (Sea)Water Splitting

Constructing transition metal multiphase composites can improve the electrocatalytic efficiency of (sea)water splitting via interfacial interaction between adjacent active sites. Herein, the self-supporting NimSn-FeOx heterostructure is in situ grown on nickel foam (NF) through a corrosion engineering approach, which displays abundant dendritic array structures, endowing the material with abundant active sites and high electrocatalytic active area. The control of introducing Fe3+ and sulfur precursors can effectively trigger the phase transiting from Ni3S2 to Ni9S8, generating more S vacancies, which could reduce the reaction energy barrier and improve the electrocatalytic performance. Simultaneously, the presence of Fe–S bonding at the sulfide/oxide interface brings a strong electronic interaction, which enables the tuning of the adsorption energy of the reaction intermediates and accelerates the catalytic reaction kinetics. As a result, the Ni9S8–FeOx/NF-Fe8.0 catalyst presents low overpotentials of 159 mV and 190 mV for oxygen evolution reaction at 100 mA cm–2 under 1 M KOH solution and simulated seawater conditions, respectively. The overall water splitting incorporating the Ni9S8–FeOx/NF-Fe8.0 as both anode and cathode provides the potential of 1.707 V in 1 M KOH and 1.794 V in simulated seawater at 100 mA cm–2. This research furnishes an efficient strategy toward the design of advanced transition metal heterogeneous composites with strong interfacial interaction for (sea)water splitting.