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

Abstract

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 (NiS 2 ) by constructing an electron-deficient distribution on Ni−S sites with N atom introduction, which efficiently inhibits the process of O 2 adsorption and electrophilic activation during oxidation, thus achieving air-stable capacity for NiS 2 . In addition, theoretical calculations further reveal that such an electronic redistribution will weaken the OH − adsorption on NiS 2 and thus inhibit the reconstruction process during the OER process. Inspired by this, NiS 2 nanosheets (NiS 2 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 NiS 2 NSs (N−NiS 2 NSs). As expected, only 28.1% of the NiS 2 phase is oxidized into sulfate nickel in N−NiS 2 NSs after one month of air exposure with only 13 mV overpotential degradation toward the OER, while for NiS 2 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−NiS 2 NSs, with an in situ constructed N−NiS 2 /NiOOH heterostructure as an OER active phase, which exhibits higher OER activity and stability compared to those of completely NiOOH-oxidized NiS 2 NSs. Rationalized by density functional theory (DFT) calculations, the N−NiS 2 /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 CoS 2 and FeS 2 ).

Insights into the Dynamic Evolution of Defects in Electrocatalysts

“…[ 80 ] Cheng and co‐workers reported that the adsorbing ability and electronic interaction for molecular oxygen could be significantly weakened in NiS 2 by constructing an electron‐deficient distribution on NiS sites with N atom introduction, which efficiently inhibits the process of O 2 adsorption and electrophilic activation during oxidation, thus achieving air‐stable capacity for NiS 2 . [ 81 ] In addition, others have created vacancy defects in catalyst itself to accelerate reaction kinetics. Our group recently studied how oxygen vacancy (Vo) dynamically changes and affects the OER in Co 3 O 4 catalyst.…”

Dual roles of sub-nanometer NiO in alkaline hydrogen evolution reaction: breaking the Volmer limitation and optimizing d-orbital electronic configuration

“…Numerous studies of transition metal-based materials including oxides, [23][24][25][26] sulfides [27][28][29] and phosphides [30][31][32][33][34] have been proven to show outstanding ability for dissociating H-OH bonds in alkaline media. 35,36 Typically, by coupling the metal Pt with transition metal oxides (TMOs), 37 the alkaline HER (A-HER) activity of the catalyst can be significantly boosted due to the synergetic catalytic effect of oxide sites with highly efficient water adsorbing and dissociating ability.…”

“…13–16 For commercial Pt catalysts, the electrocatalytic performance under alkaline conditions is observed to be significantly lower than that under acidic conditions, resulting from the weak interaction of Pt and H 2 O 17 and sluggish Volmer-step (H 2 O + e − → H* + OH − ), 18,19 caused by the high free energy of water dissociation on the full-filled 5d orbitals of Pt under an alkaline medium. 20–22 Numerous studies of transition metal-based materials including oxides, 23–26 sulfides 27–29 and phosphides 30–34 have been proven to show outstanding ability for dissociating H–OH bonds in alkaline media. 35,36 Typically, by coupling the metal Pt with transition metal oxides (TMOs), 37 the alkaline HER (A-HER) activity of the catalyst can be significantly boosted due to the synergetic catalytic effect of oxide sites with highly efficient water adsorbing and dissociating ability.…”

Strain Engineering of the NiTe/Ni2P Heterostructure to Boost the Oxygen Evolution Reaction

“…Therefore, a suitable tensile strain may significantly improve the OER performance of NiTe/Ni 2 P. However, excessive strain would lead to failure due to the lattice collapsing into another crystal phase, which coincides well with experimental results, where the NiTe/Ni 2 P with excessive strain shows apparent cracks (Figures S10, S11, and S41) when the amount of NaH 2 PO 2 reaches 2.0 g. Interestingly, the OH* adsorption free energy of Ni 2 P (201) exceeds 0 eV in the ∼5−6% tensile strain range, so the oxygen species can reversibly adsorb and desorb on the Ni 2 P (201) surface, which inhibits the irreversible phase transition of Ni 2 P into NiOOH. 63,64 Additionally, the metal salt protection layer is produced at a low voltage, therefore significantly boosting the structural stability of NiTe/Ni 2 P. On the contrary, when Ni 2 P either does not have a lattice strain or has a compressive strain, the strong adsorption of the oxygen species enhances the irreversible conversion of Ni 2 P to NiOOH. 60,61,65,66 In short, the above analysis indicates that the lattice strain between NiTe and Ni 2 P in NiTe/Ni 2 P not only can boost the OER activity of the sample by optimizing the electronic structure but also can efficiently improve the stability of catalysts by inhibiting the structurally irreversible transition caused by the continuous oxidation of the catalyst.…”