Constructing Air-Stable and Reconstruction-Inhibited Transition Metal Sulfide Catalysts via Tailoring Electron-Deficient Distribution for Water Oxidation

In promising transition metal sulfide catalysts, the extraordinary instability under air exposure and oxygen evolution reaction (OER) catalysis severely degrades their activity and stability in the electrochemical water splitting reaction, inhibiting their practical applications. Herein, guided by a theoretical mechanism study, it is disclosed that the adsorbing ability and electronic interaction for molecular oxygen will be significantly weakened in nickel disulfide (NiS2) by constructing an electron-deficient distribution on Ni–S sites with N atom introduction, which efficiently inhibits the process of O2 adsorption and electrophilic activation during oxidation, thus achieving air-stable capacity for NiS2. In addition, theoretical calculations further reveal that such an electronic redistribution will weaken the OH– adsorption on NiS2 and thus inhibit the reconstruction process during the OER process. Inspired by this, NiS2 nanosheets (NiS2 NSs) are synthesized and N atoms are introduced to bridge with Ni and S, resulting in electron-deficient Ni and S sites in N atom-bridged NiS2 NSs (N–NiS2 NSs). As expected, only 28.1% of the NiS2 phase is oxidized into sulfate nickel in N–NiS2 NSs after one month of air exposure with only 13 mV overpotential degradation toward the OER, while for NiS2 NSs, a fast and drastic phase transformation is undergone, resulting in 155 mV OER decline. For the OER process, the reconstruction from sulfides to (oxy)hydroxides is deservedly inhibited in such N–NiS2 NSs, with an in situ constructed N–NiS2/NiOOH heterostructure as an OER active phase, which exhibits higher OER activity and stability compared to those of completely NiOOH-oxidized NiS2 NSs. Rationalized by density functional theory (DFT) calculations, the N–NiS2/NiOOH heterostructure features a strong electron rearrangement at the interface, thus improving the chemisorption ability and conductivity compared to those of pristine NiOOH. Moreover, such a strategy of improving the air stability is also valid for other transition metal sulfides (TMS) (such as CoS2 and FeS2).