Hybrid Iron Oxide on Three‐Dimensional Exfoliated Graphite Electrode with Ultrahigh Capacitance for Energy Storage Applications

Electrode materials with low cost, large theoretical capacity, and fast ion/electron transport rate are highly desirable for capacitive applications. Pseudocapacitive iron oxide materials (e. g., Fe2O3, Fe3O4) satisfy the first two aspects, but are electrically/ionically insulating, hindering their practical applications in energy storage. Here, hybrid mesoporous iron oxide (Fe2O3/Fe3O4) materials are integrated with a three‐dimensional electrochemically exfoliated graphite substrate (EG) using an electrodeposition coupled with a post‐chemical transition strategy. The hybrid Fe2O3/Fe3O4 materials on EG exhibit an ultrahigh specific capacitance of 1530 F g−1 at current density of 1 A g−1. This material with such high capacitance ranks on the top of the reported iron oxide materials for capacitive applications. In addition, the assembled device with EG@Fe2O3/Fe3O4 as anode can deliver a high gravimetric energy density of 21.6 Wh kg−1 at a power density of 225 W kg−1, based on the total mass of the two electrodes (including the mass of the current collectors). This system can power various electronic devices, suggesting its great potential for energy storage applications. Exfoliate and grow: Hybrid mesoporous Fe2O3/Fe3O4 materials are grown on a three‐dimensional electrochemically exfoliated graphite substrate (EG). The hybrid Fe2O3/Fe3O4 materials exhibit ultrahigh specific capacitances of 1530 F g−1. This hybrid design is believed to substantially push the development of next generation high‐performance supercapacitor electrodes.