Strong Interface Coupling Enables Stability of Amorphous Meta-Stable State in CoS/Ni₃S₂ for Efficient Oxygen...

Rational design of heterostructure catalysts through phase engineering strategy plays a critical role in heightening the electrocatalytic performance of catalysts. Herein, a novel amorphous/crystalline (a/c) heterostructure (a-CoS/Ni₃S₂) is manufactured by a facile hydrothermal sulfurization method. Strikingly, the interface coupling between amorphous phase (a-CoS) and crystalline phase (Ni₃S₂) in a-CoS/Ni₃S₂ is much stronger than that between crystalline phase (c-CoS) and crystalline phase (Ni₃S₂) in crystalline/crystalline (c/c) heterostructure (c-CoS/Ni₃S₂) as control sample, which makes the meta-stable amorphous structure more stable. Meanwhile, a-CoS/Ni₃S₂ has more S vacancies (S_v) than c-CoS/Ni₃S₂ because of the presence of an amorphous phase. Eventually, for the oxygen evolution reaction (OER), the a-CoS/Ni₃S₂ exhibits a significantly lower overpotential of 192 mV at 10 mA cm^-2 compared to the c-CoS/Ni₃S₂ (242 mV). An exceptionally low cell voltage of 1.51 V is required to achieve a current density of 50 mA cm^-2 for overall water splitting in the assembled cell (a-CoS/Ni₃S₂ || Pt/C). Theoretical calculations reveal that more charges transfer from a-CoS to Ni₃S₂ in a-CoS/Ni₃S₂ than in c-CoS/Ni₃S₂, which promotes the enhancement of OER activity. This work will bring into play a fabrication strategy of a/c catalysts and the understanding of the catalytic mechanism of a/c heterostructures.