Nickel–cobalt–iron selenides derived from Prussian blue analog for high-energy-density asymmetric supercapacitors

Abstract Developing advanced electrode materials with high specific capacitance and a broad operating voltage range is crucial for enhancing the energy density of next-generation supercapacitors. In this study, we successfully synthesized multiphase, multilevel structured iron–cobalt–nickel selenide nanomaterials through a simple, scalable selenization treatment of a ternary metal Prussian blue analog precursor. Optimal performance was achieved through component selection. The optimized NiCoFeSe-2.25 electrode exhibits outstanding pseudocapacitive properties, with a specific capacitance as high as 447.4 F/g at 1 A/g and retaining 41.1% of its capacitance at 10 A/g, indicating excellent rate performance. An asymmetric supercapacitor (NiCoFeSe-2.25//activated carbon) assembled with this material as the positive electrode and activated carbon as the negative electrode deliver an energy density of 15.8 Wh/kg at a power density of 800 W/kg within a wide voltage window of 1.6 V. Even at a high-power density of 8000 W/kg, it maintains an energy density of 2.4 Wh/kg. Furthermore, after 5000 cycles at a current density of 3 A/g, the device retains 60.6% of its capacitance, providing an efficient and feasible PBA-derived strategy for electrode design in energy storage devices that achieve a balance between energy and power density.