Corn-straw-converted activated carbons with tunable porosity and N/O functionalities as high-performance supercapacitors electrode at commercial-level mass loading

With the scientific importance and industrial need for low-cost but high-performance activated carbons (ACs) for supercapacitors (SCs), ACs with tailorable porous texture and heteroatom doping are turned from corn straw via hydrothermal and activation processes. Porous texture is mainly adjusted by KOH/biochar mass ratio. O and N surface functionalities are tuned by a subsequent high-temperature treatment by H2O or ammonia. The influences of porosity in the amounts of the introduced N contents are investigated. With symmetric SC cells, the electrochemical performances of the corn-straw-derived ACs are examined at commercial-level mass loading. For aqueous electrolyte, the ACs prepared without KOH activation but with high-temperature treatment by ammonia exhibit high gravimetric capacitance of 192 F/g and volumetric capacitance of 150 F/cm3 due to their high compact density and N atomic fraction. For organic system, the optimum ACs are activated with KOH/biochar ratio of 1:1 and a subsequent ammonia high-temperature treatment, which deliver high gravimetric capacitance of 258 F/g and volumetric capacitance of 167 F/cm3. Balanced porosity and density, low O fraction but high N fraction are found to be favored for organic system. The cost-effective technique route may provide guidance for the design and preparation of biomass-derived ACs with tunable porosity and heteroatom functionalities for practical applications in SCs.