Experimental and theoretical investigation of high-performance supercapacitor based on guanidine functionalized graphene oxide

•Introducing guanidine functionalized GO as a high-performance supercapacitor electrode.•GO restacking prevention and interlayer distance increase via functionalization.•Providing extra pseudocapacitance as a result of guanidine functionalization.•The high specific capacitance of 612F/g at the current density of 1.5 A/g.•Superior long-term stability of 85% capacitance retention after 12,000 cycles.•Calculation of quantum capacitance using the DFT method. Functionalization of widely used graphene oxide (GO) can be beneficial not only in tuning its characteristics along with preventing the restacking of its layers and improving wettability but also in providing pseudocapacitance as a supercapacitor electrode. In this research, for the first time, the electrochemical performance of guanidine-functionalized graphene oxide (G-GO) examined by means of both computational and experimental methods. As a high-performance supercapacitor electrode, G-GO illustrates a high specific capacitance of 612F/g at the current density of 1.5 A/g together with extraordinary cyclic stability for 12,000 cycles at high current density of 10 A/g. Moreover, quantum capacitance together with the layer distance change during functionalization reaction, calculated via density functional theory (DFT), also exhibit the superior performance of G-GO.