Large surface area porous carbon materials synthesized by direct carbonization of banana peel and citrate salts for use as high-performance supercapacitors

Abstract

A facile and straightforward carbonization method for fabricating micro-/mesoporous carbons have been implemented by using different citrate salts as porogen and banana peel as the carbon precursor. Scanning electron microscopy and N2 adsorption and desorption tests show that the resultant carbon materials possess a number of micropores below 2 nm, main mesopore of 2.7–3.2 nm, and large-sized mesopore of ~ 30 nm. Besides, the surface areas of the porous carbon materials were significantly increased from 98 to 1691–2159 m2 g−1 by the introduction of citrate salts. The formation of porous structure is based on the reaction of alkali and non-alkali organic salts such as citrate salts of potassium and magnesium during the carbonization process. The as-decomposed products contain many inorganic particles (i.e. K2O or MgO) embedded within the carbon frameworks. These byproducts either acted as activator agent or acted as endotemplate in the formation of porous carbons with diverse pore sizes, which when removed by acid washing, leads to a microporous or mesoporous network. Correspondingly, electrochemical measurements show that the specific capacitance of the carbon materials improved from 59 to 258–273 F g−1 at 0.1 A g−1. And the rate capacity testing results demonstrate that the larger-sized mesoporous structures are more favorable for the transportation of electrolyte ions under high current densities. Moreover, they also exhibit good rate capability and cycling stability (more than 90% capacitance retention after 1000 cycles). These good results reveal that the as-prepared carbon materials are promising electrode material for fabrication of supercapacitor electrodes, and this method also can be used to synthesize other biomass-based porous carbon.