3D hierarchical network NiCo2S4 nanoflakes grown on Ni foam as efficient bifunctional electrocatalysts for both hydrogen and oxygen evolution reaction in alkaline solution

Abstract The development of cost-effective and high-efficiency electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) still remains highly challenging. Exposing as many active sites as possible is the key method to improve activity of HER and OER performance. In this communication, we demonstrate a novel 3D hierarchical network NiCo 2 S 4 nanoflake grown on Ni foam (NiCo 2 S 4 -NF) as a highly efficient and stable electrochemical catalyst. The NiCo 2 S 4 -NF exhibits overpotentials as low as 289 and 409 mV at 100 mA cm −2 , superior long-term durability during a 20 h measurement, and a low Tafel slope of 89 and 91 mV dec −1 for HER and OER in 1.0 M NaOH solution. The outstanding performance is owe to the inherent activity of ultrathin NiCo 2 S 4 nanoflakes and the special structure of NiCo 2 S 4 -NF that can provide a huge number of exposed active sites, accelerate the transfer of electrons, and facilitate the diffusion of electrolyte simultaneously.