Interface engineering of heterogeneous NiMn layered double hydroxide/vertically aligned NiCo2S4 nanosheet as highly efficient hybrid electrocatalyst for overall seawater splitting

Abstract

We report the fabrication of a heterogeneous catalyst through vertically aligned NiCo₂S₄/Ni₃S₂ nanosheet with encapsulation of ultrathin NiMn layered double hydroxide over self-standing nickel foam (NM/NCS/NS/NF) via two-step hydrothermal processes. Benefiting from more adequate catalytic active centres and copious interfacial charge transfer channels, NM/NCS/NS/NF electrode demonstrates superior bifunctional activity for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) processes under alkaline fresh/simulated seawater electrolyte conditions. As a result, NM/NCS/NS/NF electrode requires the smallest overpotentials of 282 & 312 mV (OER) and 171 & 204 mV (HER) to attain current densities of 30 & 50 mA cm^-2 respectively under alkaline simulated seawater electrolyte conditions. Besides, the presence of amorphous NiMn LDH layers over crystalline NiCo₂S₄/Ni₃S₂ catalyst stimulates surface adsorption of oxygen intermediate species, water dissociate ability on catalytic active centres, and mass transport with electron transfer at the interface. Further, the two-electrode configuration assisted electrolyser system delivers an efficient overall water splitting activity with minimum cell voltages of 1.54 V (in 1 M KOH) and 1.56 V (in 1 M KOH+0.5 M NaCl) at a current density of 10 mA cm^-2. Besides, a fabricated electrolyser cell provides a more sustained water electrolysis process and robust durability for 20 h which displays NM/NCS/NS/NF electrode is a vibrant and potential candidate for realistic seawater electrolysis. Therefore, our proposed heterogeneous electrocatalyst could open up a new platform for developing efficient large-scale efficient seawater electrolysis.

Keywords: Active sites; Heterogeneous catalyst; Heterointerface; Layered double hydroxide; Simulated seawater electrolysis.