Electronic Structure Tuning in Ni₃FeN/r-GO Aerogel toward Bifunctional Electrocatalyst for Overall Water Splitting

Searching for the highly active, stable, and high-efficiency bifunctional electrocatalysts for overall water splitting, e.g., for both oxygen evolution (OER) and hydrogen evolution (HER), is paramount in terms of bringing future renewable energy systems and energy conversion processes to reality. Herein, three-dimensional (3D) Ni₃FeN nanoparticles/reduced graphene oxide (r-GO) aerogel electrocatalysts were fabricated using precursors of (Ni,Fe)/r-GO alginate hydrogels through an ion-exchange process, followed by a convenient one-step nitrogenization treatment in NH₃ at 700 °C. The resultant materials exhibited excellent electrocatalytic performance for OER and HER in alkaline media, with only small overpotentials of 270 and 94 mV at a current density of 10 mA cm^-2, respectively. The good performance was attributed to abundant active sites and high electrical conductivity of the bimetallic nitrides and efficient mass transport of the 3D r-GO aerogel framework. Furthermore, an alkaline electrolyzer was set up using Ni₃FeN/r-GO as both the cathode and the anode, which achieved a 10 mA cm^-2 current density at 1.60 V with durability of 100 h for overall water splitting. Density functional theory calculations support that Ni₃FeN (111)/r-GO is more favorable for overall water splitting since the surface electronic structure of Ni₃FeN is tuned by transferring electrons from Ni₃FeN cluster to the r-GO through interaction of two metal species. Thus, the currently developed Ni₃FeN/r-GO with superior water-splitting performance may potentially serve as a material for use in industrial alkaline water electrolyzers.