Amine-assisted synthesis of the Ni3Fe alloy encapsulated in nitrogen-doped carbon for high-performance water splitting

Abstract

Developing efficient and robust catalysts for both the oxygen evolution and hydrogen evolution reaction (OER and HER) is vital for practical electrochemical water splitting. Herein, we proposed a tetraethylenepentamine (TEPA) induced thermal reduction strategy for fabricating the nitrogen-doped carbon shell encapsulated Ni₃Fe alloy catalyst (Ni₃Fe-NC/NF) from NiFe-LDH. The electrocatalyst with a 3D porous-sheet structure yields large specific surface area and exposes more active sites. The nitrogen-doped carbon (NC) shells serve as protective layers and an electron donor for modulating the electronic structure of the active center. The surface metallic state Ni and Fe species will take up OH to form hydroxide Ni and Fe species while the bulk structure of Ni₃Fe remains unchanged during electrolysis. All these properties dramatically enhance OER and HER performance in alkaline solution. Specifically, Ni₃Fe-NC/NF delivers ultralow overpotentials of 203 (OER) and 98 mV (HER) at 10 mA cm⁻², 263 (OER) and 246 mV (HER) at 300 mA cm⁻² in 1 M KOH solution. Notably, when using Ni₃Fe-NC/NF as both the anode and cathode, a small cell voltage of 1.49 V is required to achieve 10 mA cm⁻² with a nearly 100% H₂ faradaic efficiency, as well as ultralong stability at a high current of 160 mA cm⁻² for 1260 h. Besides, systematical experimental and theoretical results underline that the electron-donating ability of the NC shells and the surface generated hydroxide reduce the energy barrier of the rate-determining step, which is responsible for the high water splitting performance. This finding provides a new strategy to design advanced bifunctional catalysts toward practical overall water splitting.