Fabricating a modified biochar-based all-solid-state flexible microsupercapacitor using pen lithography

Despite an increasing interest in supercapacitors using biochar for fabricating eco-friendly energy modules, fabrication processes for most biochar-based supercapacitors are neither flexible nor easy. In this study, we fabricated an all-solid-state flexible MnO2/HNO3 pretreated biochar (NBC)/Poly(3,4-ethylenedioxythiophene) (PEDOT) composite microsupercapacitor (MSC) using pen lithography. Dispersion of biochar as ink for pen lithography was improved by HNO3 pretreatment. Specific surface area and graphitic carbon structure of the biochar were also increased by HNO3 pretreatment, resulting a high capacitance of electrochemical double layer. The fabricated MSC showed an increased pseudocapacitive behavior after adding an optimized amount of MnO2. Its capacitance was 76.6 F g−1 at 0.1 A g−1 of current density with an energy density of 14.0 Wh kg−1 at a power density of 53.1 W kg−1. The capacitive behavior of the fabricated MSC was stable over 500 bending cycles. The proposed MSC can be applied to fabricate flexible and eco-friendly energy modules.