Influence of the electrolytic medium on the performance and stability of functionalized graphene-polypyrrole nanocomposites as materials for supercapacitors

•Functionalized graphene polypyrrole nanocomposites show pure capacitive behavior in acetonitrile and high capacitance in acidic water.•Functionalization of graphene sheets by pyridine groups before electropolymerization has a positive impact on the stability of the composites.•Composites with polypyrrole are more stable than pristine graphene in acidic aqueous medium.•All graphene-polypyrrole nanocomposites display much larger capacitance retention upon cycling than polypyrrole.