Fig. 4: Characterization of cathode activation.

A Cyclic voltammetry of 1.64 mg cm⁻² active carbon on carbon cloth, measured in a Swagelok cell with a 100 µm Zn foil as the anode, and 200 µL of 15 M ZnCl₂ as the electrolyte. When the applied potential exceeded 2 V, decomposition side reactions of the electrolyte generated Cl₂ gas that increased porosity in the active carbon, as drawn in the bottom illustration. Scanning electron microscopy of active carbon B before C after the Cl₂ activation process. D Cyclic voltammetry before and after the Cl₂ gas activation, at a scan rate of 10 mV s⁻¹. E Capacity-voltage profiles of the Cl₂-activated cathode at various charge/discharge current ranging from 0.8 A g⁻¹ to 80 A g⁻¹.