Prussian blue analogue-derived Co₃O₄/Fe₂O₃ with a partially hollow and octahedral structure for high-performance...

A supercapacitor (SC) is considered as a promising energy storage device because of its high power density, fast charging/discharging speed and long cycle life. The transition metal oxides prepared by traditional methods face some challenges, such as low conductivity and uncontrollable pore size distribution. Therefore, we have prepared Prussian blue analogues (PBAs) using a coprecipitation method. By adjusting additives in the experimental process, uniform PBAs with a series of regular morphologies and structures are successfully prepared. Then the corresponding metal oxides are obtained by calcining precursors. We systematically study the influence of the morphology and structure of metal oxides Co₃O₄/Fe₂O₃ derived from PBAs on their electrochemical performance. The metal oxide with a partially hollow and octahedral structure shows excellent electrochemical performance. In a neutral electrolyte, the specific capacitance is 659.7 F g^-1 at a current density of 0.5 A g^-1. After 6000 cycles, the capacitance retention rate is 63.7%. An asymmetric supercapacitor (ASC) is constructed using Co₃O₄/Fe₂O₃ with an octahedral structure (CFMO-PVP-2) as the positive electrode and YP-50F as the negative electrode. The maximum energy density is 31.4 W h kg^-1 at a power density of 1921 W kg^-1. The maximum power density is 8421 W kg^-1 at an energy density of 23.5 W h kg^-1. The excellent electrochemical performance is attributed to the low resistance (R_w and R_ct) and high D_OH derived from the oxide particles on the surface and within the inner parts of the octahedron, which are available for electron transport. Meanwhile, the open void between adjacent nanoparticles allows the electrolyte ions to diffuse more efficiently and ensures a much more effective area for participating in a reaction. The strategy will give new insights into designing high-performance SCs based on PBAs.