Engineering the surface anatomy of an industrially durable NiCo2S4/NiMo2S4/NiO bifunctional electrode for alkaline seawater electrolysis

Abstract

Seawater electrolysis is an attractive approach for combating climate change without burdening drinking water resources. A robust electrocatalyst is required that can withstand Cl corrosion and provide excellent catalytic activity for the water splitting half-cell reactions. Here, we propose an approach for multiplying the front-line surface-active sites of a multimetallic transition metal sulfide-based electrocatalyst by depositing a monolayer amount of metal oxide. This effectively increases the number of water molecules that can dissociate per given geometrical electrode area, leading to accelerated interface kinetics. Specifically, NiCo₂S₄/NiMo₂S₄ hollow cuboids have been prepared through a multistep hydrothermal route and then coated with a monolayer amount of NiO by atomic layer deposition. A symmetrical alkaline seawater electrolyzer consisting of two bifunctional NiCo₂S₄/NiMo₂S₄/NiO electrodes delivers a current density of 430 mA cm⁻² without exceeding the hypochlorite formation threshold of 1.72 V. The in situ transformation of the oxide surface groups to oxyhydroxide groups provides good catalyst durability, requiring an overvoltage increase of only 103 mV at 1000 mA cm⁻² after 30 days of continuous electrolysis of seawater under industrially favored conditions.