General formation of Prussian blue analogue microtubes for high-performance Na-ion hybrid supercapacitors

One-dimensional (1D) hollow-structured nanomaterials with desirable compositions have aroused huge attention in the field of electrochemical energy storage. In the present study, 1D hierarchical cobalt hexacyanoferrate (CoHCF) microtubes were initially fabricated using a facile self-templated method with the electrospun polyacrylonitrile (PAN)-cobalt acetate (Co(Ac)₂) as templates. After the chemical reaction was performed between the templates and a potassium ferricyanide solution, the core-shell PAN-Co(Ac)₂@CoHCF nanofibers were successfully fabricated. Subsequently, the CoHCF microtubes were finally obtained via the selective dissolution of the PAN-Co(Ac)₂ cores. Benefiting from the unique structural characteristic, the CoHCF microtubes electrode exhibited prominent electrochemical characteristics in Na₂SO₄ aqueous electrolyte, including a high specific capacitance of 281.8 F g⁻¹ (at 1 A g⁻¹), and good rate capability as well as long cycling stability (93% capacitance retention after 5000 cycles). The hybrid supercapacitor assembled with CoHCF microtubes and activated carbon (AC) as the positive and negative electrodes, respectively, exhibited a high energy density of 43.89 W h kg⁻¹, a power density of 27.78 kW kg⁻¹, as well as a long cycle life. Note that this versatile self templated synthetic strategy could be extended to fabricate other 1D hollow Prussian blue (PB) or its analogues (PBA) with controllable composition, which have a potential application in a range of fields.