Fe-Assisted Nitridation-Induced Reconstruction of Mo-Fe-Ni Molybdates Enables Durable Alkaline Seawater Oxygen Evolution and Zn-Air Batteries

Abstract

Controlling phase evolution during nitridation is essential for creating active interfaces in multi-metal electrocatalysts. However, the nitridation pathways in complex systems such as Mo-Fe-Ni molybdates remain poorly defined. Herein, tuning the Fe contents in the Fe-Mo precursor directly governs ammonia activation and drives nitridation-induced reconstruction. Increasing Fe concentration promotes NH₃ decomposition, shifting the product from an oxide-rich phase (N-doped MoO₂-FeMoO₄-NiMoO₄-NiO, denoted N/MoO₂-MoFeNi-O) to a nitride-dominated heterostructure comprising MoO₂, Mo₂N, FeN and Ni₄N (N/MoO₂-MoFeNi-N). The optmized N/MoO₂-MoFeNi-N nitride-oxide interfaces enhance electrical conductivity, optimize oxygen-intermediate adsorption, and improve corrosion resistance. As a result, N/MoO₂-MoFeNi-N exhibits superior oxygen evolution performance in both alkaline freshwater and seawater, requiring overpotentials of only 309/392 and 334/499 mV to reach 500 and 1000 mA cm^-2, respectively. DFT calculations identify the MoO₂@FeN interface is the most active site with the lowest energetic barrier for the potential-limiting step. The catalyst also demonstrates efficient oxygen reduction activity, enabling high-performance zinc-air batteries with open-circuit voltage of 1.33 V, peak power density of 84.2 mW cm^-2, and stable cycling over 140 h. This work clarifies the role of Fe in directing nitridation pathways, providing a rational route to construct durable, interface-rich nitride-oxide architectures for advanced oxygen atalysis.