Hierarchical NMO@NiFeP reconstructed by step-current electrolysis for durable oxygen evolution in alkaline freshwater and seawater

Abstract

The development of advanced anode materials with integrated properties of superior OER catalytic activity, excellent anti-Cl⁻ corrosion stability, and long-term cycling durability has been an urgent demand in the field of seawater electrolysis for hydrogen production. Constructing amorphous–crystalline heterojunctions has emerged as a viable strategy to enhance the electrochemical performance of the anodes. Herein, a multidimensional NMO@NiFeP electrode with nanosheet-modified nanorods was prepared by a two-step approach of hydrothermal synthesis followed by electrodeposition. XRD, SEM, EDS, XPS and electrochemical tests were done to analyze the structure and the electrochemical properties in detail. The amorphous NiFeP overlayer with abundant unsaturated coordination sites was electrodeposited onto NiMoO₄ to prepare the NMO@NiFeP electrode with nanosheet-modified nanorods. The hierarchical nanorod–nanosheet architecture of the NMO substrate enables effective spatial dispersion of NiFeP nanoparticles, which synergistically boosts catalytic activity by maximizing active site exposure and optimizing mass transport. The prepared NMO@NiFeP electrode exhibits a low overpotential of 213 mV in 1 M KOH and 234 mV in alkaline seawater (1 M KOH + seawater) at 10 mA cm⁻², and exhibits a stable life after 100 h. In situ structural reconstruction of NMO@NiFeP is observed after the step-current stability test. The rod-like NMO is converted into an interconnected network with nanosheets and microspheres, while the amorphous NiFeP nanoparticles are converted into Ni(Fe)OOH nanoflower-like active phases. The reconstructed hierarchical architecture further enhances catalytic efficiency, leading to a reduction in overpotential by 6 mV at 10 mA cm⁻² and 60 mV at 100 mA cm⁻² compared to the initial state. The assembled NMO@NiFeP‖NMO@NiFeP overall water-splitting system exhibits a cell voltage of 1.675 V in alkaline freshwater and 1.704 V in alkaline seawater. It offers a promising way to develop highly active and corrosion-resistant anode materials for water and seawater electrolysis.