Potassium-ion aqueous supercapattery composed by solar carbon and nickel-zinc prussian blue analogue

Hybrid energy storage devices, currently known as supercapatteries, combine electrodes with two different energy storage mechanisms, double-layer and fast-kinetics faradaic processes, to deliver high specific energy at high specific power. Here, an eco-friendly synthetic route is employed to obtain negative (solar carbon) electrode, and a soft–chemistry route to synthesize positive (nickel-zinc hexacyanoferrate) electrode, to assemble a K-ion aqueous supercapattery. Activated carbon was synthesized by pyrolysis of agro-industrial waste composed by agave angustifolia leaves in a solar furnace, and mixed nickel-zinc hexacyanoferrate was prepared by simple chemical precipitation. Conventional three-electrode characterization of active materials showed that both materials exhibit similar rate capability and charge storage capacities. A supercapattery was obtained when combining these two electrodes, delivering specific energies of 9.163 W h kg⁻¹ and 6.444 W h kg⁻¹ at specific power values of 0.153 kW kg⁻¹ and 5.638 kW kg⁻¹, respectively. The assembled K-ion energy storage device retained 85% of the initial capacitance after 5000 cycles (at 2.5 Ag⁻¹), with a coulombic efficiency close to 100%.