Enhanced electrochemical performance of supercritical fluid aided P-doped graphene nanoflakes by I³⁻/I⁻ redox couple

Heteroatom doped graphene framework is considered as a promising candidate for electrochemical hybrid supercapacitor applications. Herein, we report the synthesis of P-doped graphene using sodium phosphate as a phosphorus source by supercritical fluid assisted processing method. The chemical nature and the quantity of P-doping in graphene are analyzed using XPS and EDAX techniques. Three different P-doped graphene samples are prepared by varying the weight ratio of graphene oxide and sodium phosphate in which the P-doped graphene with a 1:1 weight ratio (graphene oxide: sodium phosphate) exhibits a high specific capacitance of 518 F/g and capacitance retention of 98% over 5000 cycles with 1 M H₂SO₄ electrolyte. Interestingly, there could be 4-fold increase in the specific capacitance is observed after the incorporation of KI with H₂SO₄ (1772 F/g) when compared with H₂SO₄ (396 F/g) at 4 A/g. In addition, specific energy of symmetric supercapacitor with KI/H₂SO₄ (29 Wh/kg) electrolyte is 3.4-fold higher than that of H₂SO₄ (8 Wh/kg).