Cr, B Co-Doped FeS/Ni3S2 Nanosheets Supported on Nickel Foam as Electrocatalysts for Water Splitting

The electrolysis of water technology has attracted extensive research interest in hydrogen production. However, despite numerous reports on water electrolysis catalysts, research on efficient and stable transition metal-based bifunctional catalysts is still needed. Here, a Cr, B codoped FeS/Ni₃S₂ self-supported catalyst (Cr, B-FeS/Ni₃S₂) is synthesized by a hydrothermal method combined with in situ impregnation boronation. Cr, B-FeS/Ni₃S₂ exhibits outstanding oxygen evolution reaction (OER) performance, requiring only 258 and 332 mV overpotential to achieve a current density of 200 mA cm^–2 and 500 mA cm^–2, respectively. Additionally, it has a small overpotential for a hydrogen evolution reaction (HER) (η₁₀ = 102 mV) along with demonstrating favorable stability. The results show that the ultrathin, porous, wrinkled Cr, B-FeS/Ni₃S₂ nanosheets possess larger specific surface area; the superhydrophilic and superaerophobic surfaces facilitate mass transfer during the reaction. The characterizations after the reaction confirm that surface reconstruction occurs on Cr, B-FeS/Ni₃S₂, transforming sulfide into hydroxyloxide, thus promoting the OER. The codoping of Cr and B makes the active sites of Ni and Fe tend to a high valence state, which is beneficial for the occurrence of the water splitting. The DFT calculations indicate that Cr, B-FeS/Ni₃S₂ exhibits a lower reaction energy barrier in the rate-determining step of both the HER and the OER processes.