The Ni3N-encapsulated NC-layered FeOOH heterostructures are effective as OER and HER catalysts for the durable electrochemical splitting of seawater at reasonably high j values. These heterostructures can be synthesized in a scalable and sustainable manner using PAHz as a reacting and sacrificial agent. The strategy is cost-effective and devoid of ammonia and other harsh reducing agents used for conventional synthetic procedures and is suitable for further commercial implementation. The technique is also helpful in controlling the metal loading and size of metal nitride nanoparticles in the heterostructures. The procedure is general and can be extended to other metal nitride systems targeting various applications. Preliminary lab-scale testing using a two-electrode setup at RGIPT shows that the catalysts are bifunctional in nature and capable of producing H2 with acceptable faradaic efficiency. The strategy may offer pathways to the sustainable development of various composite heterostructures with tunable catalytic efficiency.