Electronic Reallocation in MOF-Derived Co4N–Ni3N Heterostructure Renders Chlorine-Free Overall Seawater Splitting under Large Current Density

As a viable method, electrocatalytic water splitting for hydrogen production, particularly in seawater, appears to be an appealing technique. Herein, the Co4N–Ni3N heterostructure was derived by controlled nitridation of a bimetallic NiCo-based metal–organic framework. The Co4N–Ni3N heterostructure shows a very low overpotential of 330 and 319 mV at a very high value of 500 mA cm–2 in alkaline freshwater for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively, and can perform at a very large current density of nearly 1.2 A cm–2 for the OER and 1 A cm–2 for the HER. Since the overpotential is less than the limit of the chlorine evolution reaction, it provides a potential platform for chlorine-free OER for seawater electrolysis. The Co4N–Ni3N catalyst exhibits exceptional durability, maintaining stability for over 230 h at 500 mA cm–2 in the OER and 100 h at 500 mA cm–2 in the HER without experiencing significant loss in the activity. For total water decomposition, Co4N–Ni3N shows a cell potential of 1.97 and 2.19 V at 500 mA cm–2 in 1 M KOH and simulated seawater, respectively. This enhanced heterostructure activity is due to a synergistic impact caused by the in situ development of the interface between Co4N and Ni3N phases during the controlled nitridation process.