P-Doped Nife Alloy-Based Oxygen Evolution Electrocatalyst for Efficient and Stable Seawater Splitting and Organic Electrosynthesis at Neutral pH

Oxygen evolution reaction (OER) is crucial for hydrogen production and organic electrosynthesis. However, its slow kinetics and inhibited water dissociation in neutral media allow for neither high efficiency nor the practical feasibility of seawater electrolysis. Moreover, impurities such as chloride ions in seawater cause electrode corrosion and undesired side reactions, such as chlorine oxidation, further compromising performance. Although seawater splitting in alkaline solutions can address chloride-related issues, alkaline conditions lead to metal ion precipitation and are incompatible with organic electrosynthesis. Nickel-iron phosphides have been shown as promising OER catalysts in alkaline environments, nonetheless, their performance under neutral conditions remains underexplored. In the present work, we developed a distinctive P-doped NiFe alloy (P:NiFe) electrocatalyst and evaluated its performance for seawater splitting under neutral-pH conditions. X-ray absorption spectra (XAS) and wavelet transform-extended X-ray absorption fine structure (WT-EXAFS) analysis at the Ni and Fe K-edges revealed the coordination of phosphorus with nickel sites within the P:NiFe structure. Following appropriate activation, the electrocatalyst demonstrated enhanced OER performance, which was attributed to the formation of high-valence nickel species and the activation of lattice oxygen. These improvements were linked to stronger metal–oxygen covalency facilitated by nickel-phosphorus coordination and the presence of Fe 3+ . The activated P:NiFe electrocatalysts also showed superior stability with remarkable corrosion resistance. This was primarily due to the formation of FePO x , which alleviates proton accumulation and prevents the dissolution of OER-active metal species. Additionally, FePO x provides robust protection against corrosion induced by chloride and hypochlorite ions, making it highly advantageous for practical seawater splitting applications. We further demonstrated that the activated P:NiFe electrodes maintained stable operation at industrially relevant current densities of 100 mA cm -2 in a flow-type electrolyzer, efficiently splitting seawater at a cell voltage of approximately 2.6 V. This work highlights the promising potential of nickel-iron phosphides for sustainable and efficient seawater splitting in real-world applications.