Controlled synthesis of mesoporous hematite nanostructures and their application as electrochemical capacitor electrodes

In this work, iron oxalate (FeC2O4 center dot 2H(2)O) with different morphologies was synthesized through a simple solution-based direct precipitation process. Three samples with distinct morphologies, i.e., microrods with a parallelogram-like cross-section, nanorods, and multi-layered nanosheets, could be obtained in a selective manner. We found that the shapes of the iron oxalate could be controlled just through simply altering the solvents used. The one-dimensional (1D) characteristic of the infinite linear chains and the selective interaction between solvents and various crystallographic planes of FeC2O4 center dot 2H(2)O played an important role in the formation of FeC2O4 center dot 2H(2)O with different morphologies. Phase-pure hematite (alpha-Fe2O3) had be obtained by annealing these as-prepared FeC2O4 center dot 2H(2)O precursors without significant alterations in morphology. The as-obtained mesoporous alpha-Fe2O3 products had high specific surface areas with narrow pore size distribution. The electrochemical properties of the alpha-Fe2O3 electrodes were investigated using cyclic voltammetry (CV) and galvanostatic charge-discharge measurements by a three electrode system. The electrochemical experiments revealed that they showed a structure-dependence in their specific capacitances. The mesoporous multi-layered nanosheets exhibited a significant structurally induced enhancement of capacity properties associated with their novel structure characteristic in addition to the high specific surface area. They can present the highest specific capacitance value (116.25 F g(-1)) and excellent long cycle life within the voltage window from -0.6 to 0 V. This method can be easily controlled and is expected to be extended to produce other functional materials with controlled structure.