Interface Engineering of Hierarchical Co9S8/Ni3S2@NiFe-LDH Heterostructures for Efficient Overall Seawater Splitting

To address the bottlenecks of poor electrical conductivity in transition metal layered double hydroxides (LDHs) and the susceptibility of transition metal sulfides to structural degradation at high oxidation potentials, this work proposes an interface engineering and multi-component synergistic strategy. Through a two-step hydrothermal-sulfidation process a Co9S8/Ni3S2@NiFe-LDH composite electrocatalyst with a hierarchical “nanorod-nanoflower” heterostructure was successfully constructed. Experimental and characterization results indicate that this three-dimensional core–shell structure not only significantly increases the electrochemically active surface area but also induces strong interfacial electronic coupling that lowers the reaction energy barrier, accelerating charge transfer and reaction kinetics. Electrochemical measurements demonstrate that in a 1.0 M KOH electrolyte, the catalyst requires an overpotential of only 96 mV for the hydrogen evolution reaction (HER) with a Tafel slope of 88.77 mV dec–1 at a current density of 10 mA cm–2; for the oxygen evolution reaction (OER), the overpotential is 174 mV with a Tafel slope of 44.96 mV dec–1. In an alkaline seawater medium, the catalyst maintains excellent bifunctional activity, delivering HER and OER overpotentials of 108.5 mV and 153.5 mV, respectively, exhibiting good tolerance to ionic interference and structural stability. Overall water splitting tests reveal that the cell voltages required to achieve a current density of 10 mA cm–2 in alkaline and seawater systems are only 1.39 and 1.43 V, respectively, and the operating voltage remains highly stable during a 50 h durability test.