Synthesis of porous carbon with low oxygen content from fulvic acid for high voltage organic supercapacitors

The operating voltage of over 3.0 V is a severe challenge for commercial supercapacitors in organic electrolyte, which raises rigorous requirements for the structure and composition characteristics of porous carbon. There are few reports regarding the construction of ultra-high voltage withstanding porous carbon derived from cheap biomass carbon sources. Herein, using cheap and renewable fulvic acid (FA) and graphene oxide (GO) as carbon precursors, the ultra-high withstanding voltage 2D porous carbon nanosheets are synthesized through KOH activation and annealing treatment, assisted by the π-π conjugation and hydrogen bonding. The incorporation of GO plays an important role in modulating the 2D nanosheet morphology of FA derived porous carbon, enhancing the e-conductivity and reducing the OFGs of porous carbons, which makes significant contribution to improving the structural stability and electrochemical performance of material. The obtained FG1% C/C composite simultaneously exhibits high specific surface area (2593 m2/g) and desirable e-conductivity (101 S m−1). More critically, it possesses highly stable surface chemical microenvironment with very-low surface oxygen content of 2.7 at.%, mainly existing as stable ether and quinone bonds. Thus, FG1% exerts ultra-high withstanding voltage up to 3.3 V in commercial TEABF4/PC electrolyte with the maximum energy density of 68.6 Wh kg−1, superior to most of the literatures, also it shows excellent stability throughout its lifespan, maintaining improved capacity retention rate (88.9%) at 2.5 A/g over 10,000 cycles. This work pares the way for the architecture design of high withstanding voltage porous carbon.