RESEARCH ARTICLE www.advmat.de Engineered Nickel–Iron Nitride Electrocatalyst for Industrial-Scale Seawater Hydrogen Production Huashuai Hu, Xunlu Wang, Zhaorui Zhang, Jiahao Liu, Xiaohui Yan, Xiaoli Wang, Jiacheng Wang, J. Paul Attfield, and Minghui Yang* Seawater electrolysis under alkaline conditions is a crucial technology for sustainable hydrogen production. However, achieving the long-term stability of the electrocatalyst remains a significant challenge. In this study, it is demonstrated that surface reconstruction of a transition metal nitride (TMN) can be used to develop a highly stable oxygen evolution reaction (OER) electrocatalyst. Rapid introduction of phosphate groups (PO 4 3− ) accelerates the in situ surface reconstruction of Ni 3 FeN, generating a catalyst, with a conductive nitride core and Cl − -resistant hydroxide shell that demonstrates outstanding performance, maintaining stability for over 2500 h at 1 A cm −2 current density in alkaline seawater. In situ characterization and density functional theory (DFT) calculations reveal the dynamic evolution of active sites, providing insights into the mechanisms driving long-term stability. This work not only introduces an efficient approach to TMN-based catalyst design but also advances the development of durable electrocatalysts for industrial-scale seawater hydrogen production. 1. Introduction The growing global demand for energy has made the de- velopment of sustainable and efficient hydrogen production technologies an urgent priority. [ 1–3] Water electrolysis has gained considerable attention as a clean and sustainable hydrogen pro- duction method. [ 4,5] In particular, alkaline seawater electrolysis offers substantial scientific and technological promise, leverag- ing the vast availability of seawater as a practical electrolyte. [ 6–8 ] H. Hu, X. Wang, Z. Zhang, J. Liu, X. Yan, X. Wang, M. Yang School of Environmental Science and Technology Dalian University of Technology Dalian 116024, China E-mail: myang@dlut.edu.cn J. Wang Zhejiang Key Laboratory for Island Green Energy and New Materials Institute of Electrochemistry School of Materials Science and Engineering Taizhou University Taizhou, Zhejiang 318000, China J. P. Attfield Centre for Science at Extreme Cosnditions and School of Chemistry University of Edinburgh King’s Buildings, Mayfield Road, Edinburgh EH9 3FD, UK The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.202415421 DOI: 10.1002/adma.202415421 However, the complex composition of seawater, particularly the presence of chloride ions (Cl − ), presents significant challenges to the stability of electrocat- alysts (Scheme 1a). [ 9–11] Cl − not only accelerates catalyst corrosion and de- activates active sites but also promotes the chlorine evolution reaction (CER), which can drastically reduce electrolytic efficiency. [ 12–14 ] Consequently, designing electrocatalysts that can resist Cl − -induced corrosion while maintaining long-term stability has become a critical focus in advancing seawater electrolysis technology. Despite numerous studies aimed at en- hancing the intrinsic stability of elec- trocatalysts or incorporating Cl − -resistant coatings, [ 12,15–20 ] a significant gap remains in achieving the high amperometric cur- rent densities required for practical seawa- ter hydrogen production (Scheme 1b). [ 21–23 ] Transition metal nitrides (TMNs) have recently emerged as promising candidates for both oxygen evolution (OER) and oxy- gen reduction reactions (ORR). [ 24–26] Their exceptional electri- cal conductivity, superior catalytic activity, and notable chemi- cal stability distinguish them from conventional oxides and hy- droxides. TMNs typically undergo in situ surface reconstruction during reactions, forming a nitride-core and hydroxide/oxide- shell structure. [ 27–30 ] This unique configuration combines the high conductivity of the nitride core with the enhanced cat- alytic activity of the hydroxide/oxide shell, offering a strategic approach to address conductivity challenges while boosting cat- alytic performance. [ 27] Exploiting this property of TMNs to ensure rapid internal charge transfer while enhancing corrosion resis- tance of the in situ formed active species presents an ideal solu- tion. In this work, we developed an ultrastable TMN electrocatalyst for seawater hydrogen production via a rapid surface phospha- tization strategy. The introduction of phosphate (PO 4 3− ) groups accelerated the in situ surface reconstruction of Ni 3 FeN, increas- ing the number of active species and significantly enhancing Cl − resistance (Scheme 1c). The resulting Ni 3 FeN@PO 4 3− /NF catalyst demonstrated exceptional electrocatalytic activity, requir- ing only 228 mV to drive 10 mA cm −2 in 1 m KOH electrolyte. Moreover, it maintained stable performance for over 2500 h under alkaline seawater conditions at an amperometric current density of 1 A cm −2 . When integrated into an anion exchange membrane water electrolyzer (AEMWE), this catalyst further Adv. Mater. 2025, 37, 2415421 © 2024 Wiley-VCH GmbH 2415421 (1 of 9)