Waste biomass valorization through production of xylose-based porous carbon microspheres for supercapacitor...

Sequential potassium hydroxide (KOH)-phosphoric acid (H3PO4) activation was applied to biomass waste to fabricate activated carbon microspheres (mCMs) with a controllable porous structure. Carbon microspheres (CMs) were first synthesized from xylose using a bottom-up approach of hydrothermal carbonization. Sequential KOH and H₃PO₄ activation was applied to the CMs in a KOH-carbon solid reaction. This created pores, which were further enlarged by adsorption of H₃PO₄. The KOH:carbon (C) and H₃PO₄:C molar ratios, and the H₃PO₄ heating rate and activation time, were varied to investigate the effect on average pore size and pore distribution. A uniform porous structure was formed without destruction of the spherical shape, and an almost 700-fold increase in surface area was obtained over the non-activated CMs. Following activation with H₃PO₄, phosphorous groups were found to be present at the surface of the carbon microspheres. The mCM was tested as a supercapacitor electrode and was shown to have a maximum specific capacitance of up to 277F g^-1. A Ragone plot showed the maximum power density to be 173.88 W Kg^-1. This increased specific capacitance was attributed to the increase in surface area and the presence of phosphorous-containing acid sites on the material surface.