Dual tuning of nickel sulfide nanoflake array electrocatalyst through nitrogen doping and carbon coating for efficient and stable water splitting

Abstract

Earth-abundant transition metal sulfide (TMS) electrocatalysts for water splitting have received extensive attention due to their low cost and bifunctional application in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Recently, introducing a nitrogen anion into 3d TMSs (N-TMSs) has been demonstrated as an effective common strategy to further improve their catalytic activity by precisely manipulating their electronic structure. However, the enhancement in the activity of the N-TMS catalysts sacrifices their stability. Herein, we present a novel strategy of dual tuning to simultaneously improve the activity and stability of TMS catalysts through nitrogen doping and carbon coating, using 3D nitrogen-doped and carbon-coated Ni₃S₂ nanoflake arrays grown on nickel foam (N-Ni₃S₂@C/NF) as a typical material. The as-prepared catalyst exhibited excellent activity for both HER and OER in 1 M KOH, as well as distinguished long-term durability (up to 140 h) even at a large current density of ∼300 mA cm⁻². The systematic experimental results reveal that the introduction of a N dopant would be beneficial for accelerating charge transfer, increasing active sites and improving intrinsic activity, whereas the amorphous carbon shell is primarily responsible for the corrosion resistance and structure stability. Finally, the electrolytic cell which consisted of N-Ni₃S₂@C/NF as both the cathode and anode only needs a very low voltage of 1.57 V to deliver a current density of 10 mA cm⁻², which is comparable to that of its Pt/C‖IrO₂ counterpart. This work provides a new strategy to design a high-performance bifunctional water-splitting electrocatalyst with both excellent catalytic activity and stability.