Preparation of nanoporous carbon microspheres by subcritical water carbonization and electrocapacitive study

In this work, sugar-derived carbon microspheres (CMSs) with diameters in the range of 5-10 μmand uniform nanopores were prepared using the subcritical water carbonization method, followed bymicrowave-assisted KOH activation. The carbonization was conducted at 3 MPa and moderate tempera-tures (150-170°C) in subcritical water, which is a green dehydrating agent. The formation of the CMSsfrom a sugar solution under subcritical water conditions followed a radical-catalysed emulsion polymer-ization mechanism. The specific surface area and pore volume of the CMSs were found to increase withincreasing the mass ratio of KOH over carbon up to 1:1. Electrocapacitive results showed that a sampleprepared at a KOH to carbon ratio of 1:1 and microwave irradiation level of 70% possessed the highestspecific capacitance (about 179.2 F/g) at a current density of 1 A/g and excellent cycling performance over1000 charging/discharging cycles without significantly loss in capacitance. The specific capacitance andcapacitive retention of this electrode are comparable to that of an electrode prepared from commercialYP-80F activated carbon