Preparation and application of iron oxide/graphene based composites for electrochemical energy storage and energy conversion devices: Current status and perspective

This review summarizes the research progresses in the preparation of graphene based iron oxide composites for electrochemical energy storage and conversion devices like lithium ion batteries, supercapacitors and fuel cells. Iron oxides (including Fe3O4, alpha-Fe2O3 and gamma-Fe2O3) are promising materials for these electrochemical devices because of their low cost, nontoxicity, good chemical stability and high theoretical capacity. However, iron oxides suffer from aggregation after reaction, poor capacity retention and low electronic conductivity. The loading of iron oxide on graphene cannot only solve these problems but also minimize the aggregation or restacking of graphene or reduced graphene oxide and enhance the properties of graphene. The high surface area, high conductivity, excellent chemical and thermodynamic stability, unique lightweight characteristic and superior optical, thermal and mechanical properties make graphene exactly excellent for applications in those electrochemical energy storage and conversion devices. The preparation of graphene based iron oxide composite therefore becomes extremely important. Hydrothermal decomposition, thermal decomposition, chemical precipitation and co-precipitation are the most frequently applied methods, which can be used for a production with a large amount of composites. Hydrothermal and thermal decomposition make a better production with higher dispersion and easier quality control. Other preparation methods, like sol-gel method, atomic layer deposition, microwave heating, plasma decomposition, electrochemical approach and hydrolysis, have also been exploited for a further improvement in the size, structure and performance control or for a simple and easy fabrication with use of fewer chemicals. No matter which method is applied, the nucleation and crystal growth of iron oxide nanoparticles on the graphene substrate are the key influencing factors but still need to be investigated. The functional groups or structure defects in graphene or reduced graphene oxide play a very important role in the nucleation and crystal growth. Many opportunities and challenges exist with the design and controllable formation of these functional-groups or structure defects. (C) 2014 Elsevier Ltd. All rights reserved.