In situ hydrothermal growth of metallic Co9S8-Ni3S2 nanoarrays on nickel foam as bifunctional electrocatalysts for hydrogen and oxygen evolution reactions

Conductivity and morphology are the two important factors affecting the performance of electrocatalysts. In this article, a facile two-step hydrothermal process was developed to grow Co9S8-Ni3S2 nanoarrays on nickel foam (Co9S8-Ni3S2 NAs/NF). The as-obtained catalyst possessed a novel morphology, in which the Co9S8 nanoneedles were surrounded by Ni3S2 ultrathin nanosheets. The resultant Co9S8-Ni3S2 nanoarrays not only permitted more exposures of active sites but also facilitated the charges and ions transport along the nanoarrays. Moreover, both Co9S8 and Ni3S2 exhibited metallic properties allowed the catalysts with conductivity (metallic conductor vs. semiconductor). Co9S8-Ni3S2 NAs/NF exhibited excellent electrocatalytic activities for both HER and OER in 1.0 M KOH solution. To reach a large current density of 100 mA cm(-2), it only required overpotentials of 204 mV and 346 mV for HER and OER, respectively. After long-term electrolysis, the high activities were still preserved. This work indicates efficient electrocatalysts can be obtained by the rational design of the heterostructure, which sheds some light on the development of noble metal-free electrocatalysts.