Scalable Green Synthesis of Ni3N-Encapsulated NC-Layered FeOOH Heterostructures: Bifunctional Electrodes for Sustainable Electrocatalytic Seawater Splitting

Abstract

Electrodes capable of electrocatalytically splitting seawater sustainably (≥500 h) at industrially acceptable current density (≥400 mA/cm2 at an overpotential of ≤0.6 V) and fabricated utilizing sustainable and scalable procedures are desirable to promote the commercialization of electrolyzer technology for green H2 production. Herewith, we report transition-metal nitride nanoparticle-encapsulated in situ-grown nitrogen-doped carbon (NC)-layered FeOOH-based heterostructures on nickel foam (NC-Ni3Nm/Fe3Nm) as bifunctional electrodes for the electrocatalytic splitting of seawater. The Ni3N/Fe3N nanoflake-encapsulated NCs are synthesized in a one-pot procedure using a sustainable route devoid of ammonia and other harsh reducing agents. Polyacryloyl hydrazide is utilized as the reducing and capping agent for the synthesis of metal nanoparticles, followed by the corresponding Ni3N-encapsulated NC under moderate temperature conditions. The procedure allows control over the metal loading and size of Ni3N nanoflakes in the heterostructures. The generality of the approach is supported by synthesizing Ni3N- and Fe3N-based heterostructures, which may be extended to other mono- and bimetallic systems. NC-Ni3N21 exhibited a bifunctional behavior (ηOER @ 100 mA/cm2 = 0.32 V, and ηHER @ 100 mA/cm2 = 0.29 V) toward the electrocatalytic splitting of seawater in the presence of 1 M KOH. The electrode displayed sustainability (≥700 h) at a fairly high current density (400 mA/cm2) in seawater under alkaline conditions.