Self-supported Ni3S2@MoS2 core/shell nanorod arrays via decoration with CoS as a highly active and efficient electrocatalyst for hydrogen evolution and oxygen evolution reactions

A hierarchically porous MoS2 on Ni3S2 nanorod array on Ni foam (MoS2/Ni3S2/NF) was firstly fabricated through a simple microwave-assisted hydrothermal method, and then followed by electrochemical deposition approach in which MoS2/Ni3S2/Ni foam is decorated with CoS (CoSMoS2/Ni3S2/NF). In contrast to conventional hydrothermal approach, microwave irradiation accelerates the synthesis of MoS2/Ni3S2/Ni foam from time of >20 h-2 h. The characterization of CoSMoS2/Ni3S2/NF by scanning electron microscope (SEM) and high resolution transmission electron microscope (HRTEM) indicate that a whole scale of 1D the Ni3S2 nanorods were hierarchically integrated with MoS2 and CoS nanosheets. The as-synthesized CoSMoS2/Ni3S2/NF hybrid not only endows the ease transport of electrons along Ni3S2 nanorods to Ni foam, but also accommodates maximal exposure of active edge sites to the reactants through hierarchically porous CoS doped MoS2 nanosheets, accomplishing the promoted kinetics and activity for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). By electrochemical measurements such as linear sweep voltammetry (LSV) and electrochemical impedance spectroscope (EIS), we find that the CoSMoS2/Ni3S2/NF hybrid shows markedly enhanced electrochemical performance for both HER and OER. Specifically, the optimal CoSMoS2/Ni3S2/NF8C possesses the low overpotentials (η10) of 85 and 225 mV at current density (|j|) of 10 mA cm−2 in 1.0 M KOH and the small 62.3 and 46.1 mV dec−1 Tafel slope for HER and OER, respectively, outperforming those of most of the current noble metal-free electrocatalysts. These results highlight the fact that CoSMoS2/Ni3S2/NF is a high-performance, noble-metal-free electro-catalyst, and provide a potential avenue toward achieving an enhanced electrocatalytic activity towards both in HER and OER. Yet the duration of the as prepared catalyst in OER still need to be improved.