Nanostructured Iron Oxide/Hydroxide‐Based Electrode Materials for Supercapacitors

There is a pressing need to further increase the energy density of supercapacitors to meet the requirements of next‐generation electronic devices. One promising solution is to develop advanced electrode materials with large capacitance at fast charge/discharge rates. Among the newly developed electrode materials for supercapacitors, iron oxides/hydroxides have recently emerged as a promising class of anode materials largely because of their attractive electrochemical performance, source abundance, low price, and environmental friendliness. However, the use of these emerging materials in practical set‐ups is unfortunately curtailed by their relatively small surface area and poor electrical conductivity, which could pose detrimental effects on their pseudocapacitive performance. Recently, material scientists and chemists in the energy community have attempted to address these materials’ challenges by taking the advantage of the unique physical and chemical properties of iron oxides/hydroxides at the nanoscale size regime, which are the key topics discussed in this Focus Review. Here, we first summarize recent advances in the development of high‐performance iron oxide/hydroxide‐based electrode materials, and their use as anode materials in asymmetric supercapacitors. We then highlight and exemplify several effective design strategies, such as architectural design, chemical modification, and multifunctional composites of iron oxide/hydroxide‐based electrodes, to further improve their electrochemical properties. In the last section, we discuss the challenges and perspectives in this exciting field, shedding some light on the design of iron oxide/hydroxide‐based electrodes for practical applications.