Graphene-like biochars from pyrolysis of sugarcane bagasse and exhausted black acacia bark for the production of supercapacitors

Sugarcane bagasse and exhausted black acacia bark biomass residues were pyrolyzed at high temperatures to obtain biochars with structures analogous to graphene oxide, as an economically viable destination for these waste materials. The biomasses were subjected to pretreatment with water and dilute nitric acid, followed by pyrolysis at 900 °C in an atmosphere of isopropanol vapor with N₂. Additionally, pyrolysis was conducted under the same conditions without pretreatment (with isopropanol) and with only a nitrogen flow for comparison. The biochars obtained by pyrolysis with isopropanol presented lower H/C ratios, indicating high graphitization, and more stable O/C ratios, with characteristics of graphene-like material or graphene oxides. The biochars were used to modify electrodes, together with polyaniline (PANI). The electrodes modified with PANI and the biochars with isopropanol vapor showed specific capacitances (C_s) up to 2.7-fold higher than for the electrode modified with PANI alone, with the high C_s values maintained even after 1000 charge and discharge cycles, as well as significantly increased capacitive currents. Pyrolysis with isopropanol proved to be an effective and fast method that conferred different biochar characteristics, compared to the biochars produced by pyrolysis in N₂ alone. These results are promising for the development of high-performance supercapacitors with low production costs.