Scalable Green Synthesis of Ni<sub>3</sub>N-Encapsulated NC-Layered FeOOH Heterostructures: Bifunctional Electrodes for Sustainable Electrocatalytic Seawater Splitting
Arpan Tewary, Subhankar Mandal, Zahoor Alam, Akhoury Sudhir Kumar Sinha, Umaprasana Ojha
Abstract
Electrodes capable of electrocatalytically splitting seawater sustainably (≥500 h) at industrially acceptable current density (≥400 mA/cm 2 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 H 2 production. Herewith, we report transition-metal nitride nanoparticle-encapsulated in situ-grown nitrogen-doped carbon (NC)-layered FeOOH-based heterostructures on nickel foam (NC-Ni 3 Nm/Fe 3 Nm) as bifunctional electrodes for the electrocatalytic splitting of seawater. The Ni 3 N/Fe 3 N 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 Ni 3 N-encapsulated NC under moderate temperature conditions. The procedure allows control over the metal loading and size of Ni 3 N nanoflakes in the heterostructures. The generality of the approach is supported by synthesizing Ni 3 N- and Fe 3 N-based heterostructures, which may be extended to other mono- and bimetallic systems. NC-Ni 3 N21 exhibited a bifunctional behavior (η OER @ 100 mA/cm 2 = 0.32 V, and η HER @ 100 mA/cm 2 = 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/cm 2 ) in seawater under alkaline conditions.