Strong Interface Coupling Enables Stability of Amorphous Meta-Stable State in CoS/Ni3 S2 for Efficient Oxygen Evolution.

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/Ni3 S2 ) is manufactured by a facile hydrothermal sulfurization method. Strikingly, the interface coupling between amorphous phase (a-CoS) and crystalline phase (Ni3 S2 ) in a-CoS/Ni3 S2 is much stronger than that between crystalline phase (c-CoS) and crystalline phase (Ni3 S2 ) in crystalline/crystalline (c/c) heterostructure (c-CoS/Ni3 S2 ) as control sample, which makes the meta-stable amorphous structure more stable. Meanwhile, a-CoS/Ni3 S2 has more S vacancies (Sv ) than c-CoS/Ni3 S2 because of the presence of an amorphous phase. Eventually, for the oxygen evolution reaction (OER), the a-CoS/Ni3 S2 exhibits a significantly lower overpotential of 192 mV at 10 mA cm-2 compared to the c-CoS/Ni3 S2 (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/Ni3 S2 || Pt/C). Theoretical calculations reveal that more charges transfer from a-CoS to Ni3 S2 in a-CoS/Ni3 S2 than in c-CoS/Ni3 S2 , 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.