Tremella-like Ni3S2/MnS with ultrathin nanosheets and abundant oxygen vacancies directly used for high speed overall water splitting

The development of highly active and stable non-noble metal electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) bifunctional performances is crucial for efficient water splitting. In this work, such electrocatalysts are obtained, first in two-step hydrothermal reactions to form Ni3S2/MnS nanosheets on Ni foam (NF/Ni3S2/MnS), then by slightly electroxidizing the Ni3S2/MnS to generate tremella-like Ni3S2/MnS-O with ultrathin nanosheets and abundant oxygen vacancies (denoted as NF/T(Ni3S2/MnS-O)) favorable for electrocatalyzing HER and OER. Benefiting from the abundant oxygen vacancies, tremella-like ultrathin nanosheets with hierarchical porous structure and large active surface area, NF/T(Ni3S2/MnS-O) shows high catalytic performance, including lower overpotential and electrochemistry stability for both HER and OER than so far reported MnOx and other metal oxides/sulfides. The NF/T(Ni3S2/MnS-O) directly used as bifunctional electrodes for overall water splitting exhibits a low voltage of 1.54 V with a low overpotential of 0.31 V at a current density of 10 mA cm−2, a fast H2 and O2 evolution speed of 4.13 and 2.04 μmol min−1 and a good electrochemistry stability with unchanged current density of 10 mA cm−2 for 50 h.