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 NH₃-treated oxide-dominant phase with partial nitrogen incorporation (MoO₂, FeMoO₄, NiMoO₄, and NiO, denoted as N/MoO₂–MoFeNi–O) to a nitride-dominated heterostructure comprising MoO₂, Mo₂N, FeN and Ni₄N (N/MoO₂–MoFeNi–N). The optimized N/MoO₂–MoFeNi–N nitride–oxide interfaces enhance conductivity, regulate adsorption, and strengthen 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 as 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 an open-circuit voltage of 1.33 V, a 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 catalysis.