Constructing graphene-based heterostructures with large interfacial area is an efficient approach to enhance the electrochemical performance of supercapacitors but remains great challenges in their synthesis. Herein, a novel ultra-small amorphous Fe₂O₃ nanodots/graphene heterostructure (a-Fe₂O₃ NDs/RGO) aerogel was facilely synthesized via excessive metal-ion-induced self-assembly and subsequent calcination route using Prussian blue/graphene oxide (PB/GO) composite aerogel as precursors. The deliberately designed a-Fe₂O₃ NDs/RGO heterostructure offers a highly interconnected porous conductive network, large heterostructure interfacial area, and plenty of accessible active sites, greatly facilitating the electron transfer, electrolyte diffusion, and pseudocapacitive reactions. The obtained a-Fe₂O₃ NDs/RGO aerogel could be used as flexible free-standing electrodes after mechanical compression, which exhibited a significantly enhanced specific capacitance of 347.4 F·g⁻¹ at 1 A·g⁻¹, extraordinary rate capability of 184 F·g⁻¹ at 10 A·g⁻¹, and decent cycling stability. With the as-prepared a-Fe₂O₃ NDs/RGO as negative electrodes and the Co₃O₄ NDs/RGO as positive electrodes, an all-solid-state asymmetric supercapacitor (a-Fe₂O₃ NDs/RGO//Co₃O₄ NDs/RGO asymmetric supercapacitor (ASC)) was assembled, which delivered a high specific capacitance of 69.1 F·g⁻¹ at 1 A·g⁻¹ and an impressive energy density of 21.6 W·h·kg⁻¹ at 750 W·kg⁻¹, as well as good cycling stability with a capacity retention of 94.3% after 5,000 cycles. This work provides a promising avenue to design high-performance graphene-based composite electrodes and profound inspiration for developing advanced flexible energy-storage devices.

With excellent theoretical capacities, transition-metal phosphides (TMPs) have been recognized as promising anode materials for potassium-ion batteries (KIBs) but there remain considerable challenges in improving the structural stability and electrochemical performance. Moreover, the electrochemical reaction mechanism of TMP-based KIB anodes is still unclear and mostly unexplored. Herein, we elaborately design a flexible and hierarchically porous anode consisting of discrete FeP hollow nanospheres well encapsulated within a three-dimensional graphene skeleton (3DG/FeP) via a novel spatially confined one-step thermal transformation strategy using a 3DG/metal–organic framework (MOF) as the precursor for the first time. The unique architecture provides interconnected porous conducting network and tight contact between graphene and FeP hollow nanospheres as well as sufficient stress buffer nano-hollow spaces to greatly promote the charge transport and maintain the structural integrity. Thus, the 3DG/FeP anode delivers a high reversible capacity of 323 mA h g⁻¹ at 0.1 A g⁻¹ and ultrastable cycle performance with a capacity retention of 97.6% at 2 A g⁻¹ after 2000 cycles, which is almost the best result among all the reported FeP anodes for KIBs. Further detailed characterizations not only elucidate 3DG confinement-promoted microphase separation and nanoscale Kirkendall effects of MOF but also explore the multiple reversible intercalation and conversion processes of K⁺ insertion/extraction in the FeP component.

Exploration of electrode materials with well-defined nanostructures and good flexibility is an efficient approach for achieving high-performance and flexible energy storage systems. However, it is still challenging to well integrate active materials into flexible electrodes and simultaneously maintain satisfactory electrochemical performance. Herein, we successfully synthesize novel three-dimensional graphene (3DG)-encapsulated porous multishelled NiO hollow microsphere (3DG/pMS-NiO) composite aerogels via a modified self-templating method and a dopamine (DA)-assisted self-assembly route. The well-designed highly interconnected porous 3DG network and the close contact NiO–graphene structure of the 3DG/pMS-NiO composite aerogels offer multiple advantages such as high porosity and accessible area, improved conductivity, enhanced electrolyte diffusion and a simple electrode preparation process. Thus, the as-prepared flexible 3DG/pMS-NiO electrodes showed significantly improved specific capacitance of 710.4 F g⁻¹ at 0.5 A g⁻¹ and excellent rate capability with an ultrahigh capacitance retention of 92.5% at 10 A g⁻¹. In addition, the fabricated asymmetric supercapacitors (3DG/pMS-NiO//AC) showed a high specific capacitance of 34.4 F g⁻¹ at 1 A g⁻¹ with a voltage window of 0–1.6 V, a large energy density of 12.3 W h kg⁻¹ at a power density of 815.3 W kg⁻¹, and a decent cycling stability. This work profoundly enlightens the material design and electrode preparation, and even opens up an avenue for the development of high-performance and flexible energy storage systems.