Spongy porous carbon nanosheets obtained by one-step oxidation-activation of asphalt with KHC2O4 activator: Application in the cathode of zinc storage devices

Porous carbon (PC) is widely used in Zn-based electrochemical devices (e.g., zinc ion capacitors and zinc iodine batteries), whose synthesis by conventional methods often leads to severe corrosion and high energy consumption. A novel activator, KHC2O4, was selected to activate three types of asphalt precursors (medium/high-temperature coal asphalts and petroleum asphalt) to obtain three kinds of PCs (MCA-C, HCA-C, and PA-C) via a green routine. Meanwhile, we also explored the chemical composition of asphalt on the structure, morphology, and electrochemical properties of PCs. Three asphalt samples from different sources are all feasible to synthesize porous carbon nanosheets by the convenient one-step oxidation-activation method using a KHC2O4 activator attenuating the conjugation effect of asphalt and reducing energy consumption. Among them, PA-C obtained from petroleum asphalt presents a unique twisted spongy sheet-like structure with the help of the foaming function from KHC2O4, which is favorable for ion storage. PA-C possesses a high specific capacitance of up to 348.1 F/g (0.5 A/g) in a three-electrode system. The ZIC (Zn ion capacitor) with the cathode selected PA-C exhibits a 184.2 mAh/g (0.1 A/g) specific capacity and high energy density of 147.4 Wh/kg (100 W/kg). Moreover, PA-C/I obtained by compositing PA-C with iodine also achieves 250.9 mAh/g in the cathode of ZIOB (zinc-iodine battery). Consequently, this work has successfully realized the transformation of cheap asphalt into high-value-added functional materials.