Recent progress of Ni-Fe layered double hydroxide and beyond towards electrochemical water splitting.

The electrochemical water splitting process including the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is considered as one of the most promising methods for high-purity hydrogen production. Ni-Fe based compounds, especially Ni-Fe layered double hydroxide (LDH), have become highly efficient electrocatalysts to expedite the above reactions. During the last decade, great progress has been witnessed in the development of Ni-Fe based electrocatalysts. Diverse regulatory strategies such as morphology modulation, composition control, and defect engineering have been employed to optimize their electrochemical performances for water splitting. In addition, the family of Ni-Fe based compounds has been expanded from LDHs to alloys, sulfides, phosphides and so forth. Deep experimental investigations and theoretical studies have also been carried out to reveal the intrinsic origin of the superior electrocatalytic performances. In this review, we summarise the recent development of Ni-Fe based compounds for electrochemical water splitting with high efficiency. Special focus has been placed on the design principle and synthetic strategies of Ni-Fe based compounds. In the end, remaining challenges and future research directions are briefly discussed.