N,O co-doped hierarchical nanoporous biochar derived from waste cigarette butts for high-performance energy-storage application

Abstract

There are about 8 million tons of discarded cigarette butts generated annually worldwide. The green and efficient use of them is urgently needed. Cigarette butts are waste cellulose-based materials consisting of the outer packaging (cellulose) and the filter tip (cellulose acetate) that are good candidates to be resourcefully utilized. Herein, N,O co-doped hierarchical nanoporous biochars (CNPBs) with uniform morphology are readily prepared from cigarette butts via hydrothermal carbonization, coupled with pyrolysis activation. The hierarchical pore structure and surface properties of the prepared biochars could be expediently controlled by adjusting the activator ratio and activation temperatures. The optimal CNPB, which has a high specific surface area (2,133.5 m² g⁻¹), excellent microporosity, and oxygen-rich properties, is obtained at the activation temperature of 700 °C with a potassium hydroxide ratio of 4 (CNPB-700-4). CNPB-700-4 exhibits an energy storage capacity of up to 344.91 F g⁻¹ at a current density of 1 A g⁻¹. After 10,000 constant charge/discharge cycles at a current density of 10 A g⁻¹, the capacity remains at 95.44%. The energy density and power density of the assembled CNPB-700-4//CNPB-700-4 symmetrical supercapacitors are 24.33 Wh kg⁻¹ and 373.71 W kg⁻¹, respectively, demonstrating the high commercial value of the prepared material.