Battery-type hollow Prussian blue analogues for asymmetric supercapacitors

Hollow/porous nanomaterials are widely applicable in various fields. The last few years have witnessed increasing interest in the nanoscale Kirkendall effect as a versatile route to fabricate hollow/porous nanostructures. The transformation of Cu-Co Prussian blue analogue (CuCo-PBA) and FeFe-PBA nanocubes into CuO/Co₃O₄ and Fe₂O₃ nanoframes is based on two types of nanoscale Kirkendall effect, which are related to solid-solid interfacial oxidation and solid-gas interfacial reaction, respectively. Both CuO/Co₃O₄ and Fe₂O₃ nanoframe electrodes exhibit high reversible discharge capacity, good rate performance and long cycling stability. Moreover, an asymmetric supercapacitor (ASC) is assembled by using CuO/Co₃O₄ as a cathode and Fe₂O₃ as an anode, respectively. The ASC can be operated in a wide potential range of 1.4 V with a large specific capacity of 181.8 F g^-1, a high energy density of 48.77 W h kg^-1 (at 751.2 W kg^-1), an outstanding power density of 3657.8 W kg^-1 (at 32.9 W h kg^-1) and a good capacity retention (73.68%) after 6000 galvanostatic charge-discharge cycles, together with excellent flexibility. The ASC in series can power a LED and work stably under water conditions, delivering excellent practicability.