A two-step thermal treatment method to produce reduced graphene oxide with selectively increasing electrochemically active carbonyl group content for high-performance supercapacitor electrode

The variation of oxygen functional groups (OFGs) is extremely complicated during the thermal treatment of graphene oxide (GO). Selectively improving the content of electrochemically active OFGs through multi-step thermal treatment is a promising strategy to enhance the charge storage capability of graphene-based supercapacitor electrodes. In this work, a two-step thermal treatment method was used to produce reduced graphene oxide (RGO) with selectively increasing the content of electrochemically active quinone-type carbonyl groups (C˭O). The first step is thermal reduction at 500 °C in Ar atmosphere, during which GO is exfoliated into separated sheets with porous structure and larger surface area; the second step is air oxidation at 400 °C, which facilitates the selective formation of quinone-type C˭O groups and enhances the mesoporous fraction. Due to the pseudocapacitive behavior of quinone-type C˭O groups and low ion diffusion resistance, the electrode prepared by RGO exhibits a high specific capacitance of 303 F g⁻¹ at 0.2 A g⁻¹ with excellent rate capability (202 F g⁻¹ at 10 A g⁻¹) and notable cycling performance (~ 116% capacitance retention after 1500 cycling at 1 A g⁻¹). The present work proposed a facile and environmentally friendly two-step thermal treatment strategy in effectively controlling the surface property and microstructure of graphene materials, which has significant implications for mass producing graphene materials for supercapacitor electrodes.