Heterostructured metal oxides realized by quenching-induced structural transformation

Abstract

Heterostructured metal oxides exhibit outstanding catalytic performance in various chemical/electrochemical reactions, yet still face the bottleneck of synthesis difficulty and insufficient control over the catalyst composition. Herein, a facile synthesis route for heterostructured metal oxides via quenching-induced structural transformation was developed, and the size effect and the promotion mechanism between multiple quenching are also presented. Repeated quenching of hot NiMoO₄ powders with a broad range of initial particle size in cold Fe(NO₃)₃ solution yielded different products depending on the initial NiMoO₄ particle size and quenching frequency. Significant disorder and a roughened surface were created on the large-grained NiMoO₄ nanoparticles (>27 nm), whilst for smaller NiMoO₄ nanoparticles (<27 nm), multiple quenching triggered the structural transformation from NiMoO₄ to NiFe₂O₄ to create a novel NiMoO₄/NiFe₂O₄ heterostructure. We further found that the disordered defect structure generated by pre-quenching can promote the subsequent quenching regulation, and the minimization of particle size was more sensitive to quenching and thus was regulated as a whole, overcoming the thermodynamic bottleneck. The NiMoO₄/NiFe₂O₄ heterostructured nanocatalyst demonstrated remarkable catalytic activity for oxygen evolution and reduction reactions in alkaline media, thus delivering excellent electrochemical performance in rechargeable zinc–air batteries. Our findings provide novel inspiration for the preparation of highly active heterostructured metal oxide nanocatalysts, which can be applied to various oxides, such as CoMoO₄/CoFe₂O₄.