Deep eutectic solvent-induced synthesis of Ni–Fe catalyst with excellent mass activity and stability for water oxidation

Abstract

Ni–Fe bimetallic electrodes are currently recognized as a kind of benchmark transition metal-based oxygen evolution reaction (OER) electrocatalysts. Facile synthesis of Ni–Fe bimetallic electrode materials with excellent catalytic activity and satisfied stability by a simple and low-cost route is still a big challenge. Herein, well-defined Ni–Fe nanoparticles in-situ developed on a planar Fe substrate (Ni–Fe NPs/Fe) is fabricated via a facile one-step galvanic replacement reaction (GRR) carried out in an Ethaline-based deep eutectic solvent (DES). The prepared Ni–Fe NPs/Fe exhibits outstanding OER performance, which needs an overpotential of only 319 mV to drive a current density of 10 mA cm−2, with a small Tafel slope of 41.2 mV dec−1 in 1.0 mol L−1 KOH, high mass activity (up to 319.78 A g−1 at an overpotential of 300 mV) and robust durability for 200 h. Impressively, the Ni–Fe bimetallic oxygen-evolution electrode obtained from the Ethaline-based DES is catalytically more active and durable than that of its counterpart derived from the 4.2 mol L−1 NaCl aqueous solution. The reason for this is mainly related to the different morphology and surface state of the Ni–Fe catalysts obtained from these different solvent environments, particularly for the differences in phy–chemical properties, active species formed and deposition kinetics, offered by the Ethaline-based DES.