High-temperature-induced phase transformation of FeMoO4 into Fe2Mo3O8-based catalysts for alkaline water/seawater oxidation

It is crucial to rationally design multi-component composite catalysts with high activity and strong stability for electrolytic water/seawater oxidation. In this work, we synthesized porous rod-like Ni–Fe 2 Mo 3 O 8 @NC catalysts via high-temperature phase transformation of FeMoO 4 into Fe 2 Mo 3 O 8 , melamine pyrolysis, and Ni-doping. Specifically, high-temperature anoxic environment and lattice oxygen release trigger partial Mo 6+ reduction and Fe 2+ oxidation in FeMoO 4 . The monoclinic FeMoO 4 undergoes phase transition to form hexagonal Fe 2 Mo 3 O 8 with mixed valence characteristics, enabling original rod-like structure retention, as well as active site density and electron transport efficiency enhancement. Meanwhile, via hot solvent method, the lone pair electrons of N atoms in melamine coordinate with empty d-orbitals of metal ions in Ni–FeMoO 4 , forming strong coordination bonds. Subsequent high-temperature carbonization accomplishes melamine pyrolysis with NH 3 evolution, which etches rod-like Ni–Fe 2 Mo 3 O 8 to form porous structure. Simultaneously, the synergistic interaction among Ni–Fe–Mo can optimize reaction intermediates adsorption energy, thereby enhancing material catalytic performance.