Ion doping in transition metal oxides is always considered to be one of the most effective methods to obtain high-performance electrochemical supercapacitors because of the introduction of defective surfaces as well as the enhancement of electrical conductivity. Inspired by the smelting process, an ancient method, quenching is introduced for doping metal ions into transition metal oxides with intriguing physicochemical properties. Herein, as a proof of concept, α-Fe₂O₃ nanorods grown on carbon cloths (α-Fe₂O₃@CC) heated at 400 °C are rapidly put into different aqueous solutions of alkaline earth metal salts at 4 °C to obtain electrodes doped with different alkaline earth metal ions (M-Fe₂O₃@CC). Among them, Sr-Fe₂O₃@CC shows the best electrochemical capacitance, reaching 77.81 mF cm⁻² at the current of 0.5 mA cm⁻², which is 2.5 times that of α-Fe₂O₃@CC. The results demonstrate that quenching is a feasible new idea for improving the electrochemical performances of nanostructured materials.