Electrostatic repulsion and interface engineering in the low-crystalline/crystalline Ni3N@NiFeHPOx heterostructure toward enhanced alkaline water and seawater splitting.

Abstract

Designing nanoheterostructures and optimizing the interfacial microenvironment are critical yet challenging strategies for enhancing the performance of transition metal nitride electrocatalysts. In this study, a novel heterostructured catalyst consisting nickel nitride nanosheets wrapped by NiFe bimetallic hydrogen phosphate (Ni₃N@NiFeHPO_x) is constructed on nickel foam (NF), aiming at efficient hydrogen production in both alkaline water and seawater electrolysis. The heterointerface between low-crystalline NiFeHPO_x and crystalline Ni₃N enhanced the hydrophilicity and optimized the intermediate adsorption/desorption during water splitting. Meanwhile, the electrostatic repulsion caused by coordinated HPO_x^2- formed a chloride-ion-resistant layer at the catalyst-electrolyte interface, significantly improving the corrosion resistance to chloride ions in seawater. These synergistic effects endow the catalyst with excellent catalytic activity and stability for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in both alkaline water and seawater. The dual-electrode system integrating Ni₃N@NiFeHPO_x/NF as both the anode and cathode delivers a current density of 10 mA·cm^-2 at cell voltages of 1.514 and 1.506 V in alkaline water and seawater, respectively. This study underscores the potential of composite materials with engineered heterointerfaces and finely tuned interfacial microenvironments to address critical challenges in water and seawater electrolysis, paving the way for developing more efficient and durable catalysts for hydrogen production from seawater.