In-Situ Transformed Ni, S-Codoped CoO from Amorphous Co–Ni Sulfide as an Efficient Electrocatalyst for Hydrogen Evolution in Alkaline Media

Amorphous materials have recently received much attention as catalysts for electrochemical reactions. However, there are relatively few reports focused on the structure change of amorphous catalysts during the catalysis process, although this is quite important to the identification of active species and in revealing the reaction mechanism. Herein, amorphous Co–Ni sulfide in the form of a nanoplate and nanowire hybrid on the surface of nickel foam is prepared as the electrode for the hydrogen evolution reaction (HER). During the hydrogen evolution process, the amorphous Co–Ni sulfide is in-situ transformed into crystalline Ni, S-codoped CoO which is actually responsible for the catalysis of HER. The transformation process is studied in detail by high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and theoretical calculations. The in-situ formed electrode presents a high activity and durability toward HER in alkaline media. The Ni and S dopants, sulfurization temperature, and electrode substrate are revealed to be important factors that affect the activity. The present work will not only give more insights in the structure evolution of the electrocatalyst during HER but also provides a new strategy to the fabrication of new electrocatalysts.