A comprehensive analysis of Sargassum natans-derived inorganic carbon composite for electrochemical charge storage

Converting the sargassum seaweeds - a naturally occurring pelagic coastal waste - to highly conducting and porous carbon (via high-temperature carbonization) can be a strategically useful method for obtaining low-cost materials suitable for supercapacitor applications. In this manuscript, the facile synthesis and fascinating electrochemical capacitive behavior of KOH-activated carbonized Sargassum natans (S. natans) seaweed are reported. The physicochemical results suggest that the initial carbonization of sargassum leads to formation of CaS, MgO, and CaCO3 (in its amorphous phase-aragonite) particles within the carbon matrix. The subsequent KOH- activation of the carbonized sargassum not only enhances the carbon porosity and surface area, but also leads to the elimination of CaS and causes a phase transformation of aragonite to crystalline Mg-rich calcite. The electrochemical measurements (conducted in 6.0 M KOH electrolyte) show a tremendous rise in the specific capacitance value (similar to 23 times) with the KOH-activated carbon samples compared to those of their non-activated counterparts. The S. natans which is carbonized at 700 degrees C, and subsequently activated with KOH (denoted as 'C@S-700A') exhibits a surface area of 1510 m(2) g(1) and also shows a maximum specific capacitance of 276.5 F g(-1) at 0.25 A g(-1). In a device configuration, an energy density of 3.458 Wh kg(-1) is obtained with C@S-700A at 150 W kg(-1). The improved electrochemical capacitance observed after KOH-activation is attributed to the calcite enrichment, increased material porosity and enhanced surface area of the carbonized S. natans.