Multifunctional Iron Oxide Nanoflake/Graphene Composites Derived from Mechanochemical Synthesis for Enhanced Lithium Storage and Electrocatalysis

Composites consisting of nanoparticles of iron oxides and graphene have attracted considerable attention in numerous applications; however, the synthesis methods used to achieve superior functionalities are often complex and unamenable to low-cost large-scale industrial production. Here, we report our findings in exploring a simple strategy for low-cost fabrication of multifunctional composites with enhanced properties. In particular, we have successfully prepared FeO(OH) nanoflake/graphene and nano-Fe₃O₄/graphene composites from commercially available Fe powders and graphite oxides using a simple and low-cost solid-state process, where the metallic Fe is converted to FeO(OH) nanoflake and graphite oxide is reduced/exfoliated to graphene. The resultant nano-Fe₃O₄/graphene composite is multifunctional, demonstrates specific capacities of 802 and 629 mA h g^-1, respectively, at 1000 and 2000 mA g^-1 as an electrode material for lithium-ion batteries (LIBs), and also displays efficient catalytic activity for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER); the nominal overpotentials are lower than those for previously reported metal-based catalysts (e.g., IrO₂, RuO₂, and Pt/C). The dramatically enhanced properties are attributed to the synergistic mechanochemical coupling effects between iron oxide and graphene introduced by the facile process, which is well suited for large-scale cost-effective fabrication.