Solution combustion synthesis of nanostructured iron oxides with controllable morphology, composition and electrochemical performance

Nanostructured iron oxides have emerged as promising materials for electrochemical energy storage and conversion devices due to their high theoretical capacity, eco-friendliness and earth abundance. Particularly, the morphology- and composition-controllable synthesis of nanostructured iron oxides is extremely important to optimize their electrochemical performance. However, the development of facile and effective synthetic method is still a great challenge. In this paper, we demonstrated a one-pot solution combustion synthesis (SCS) approach for the time- and energy-effective preparation of nanostructured iron oxides with controllable morphology and composition just by tuning the molar ratio (φ) of fuel (glycine) to oxidizer (ferric nitrate). Innovatively, the effects of φ value on the control of combustion reaction mechanism, morphology and composition of SCS products, and the electrochemical properties in relation to the morphology and composition have been systematically investigated. The results revealed that with the increase of φ value, the reaction mechanism varied from pyrolysis to combustion and the combustion phenomenon changed from volumetric mode to self-propagating mode. Correspondingly, the morphology of products evolved from uniform nanoneedles to porous nanosheets, and finally into aggregated nanoparticles. Meanwhile, the phase composition of these products changed from amorphous α-Fe2O3 to crystalline α-Fe2O3, and eventually into α-Fe2O3/Fe3O4 composites. When evaluated as lithium ion battery anode, the as-prepared α-Fe2O3/Fe3O4 porous nanosheets (φ = 1.0 product) exhibited the best electrochemical properties (a high reversible capacity of ~ 1200 mA h g−1 and an excellent rate capability) among all the SCS products, which may be attributed to its mesoporous structure (supply favorable accessibility for electrons), nanosheet morphology (shorten the transport length of Li+) and appropriate proportion of Fe3O4 phase (enhance the electronic conductivity). Consequently, the facile SCS method demonstrated here might provide a new methodology for the morphology and composition-controllable synthesis of nanomaterials, for which a number of prospective applications in electrochemical fields can be envisioned.