Synthesis of amino-functionalized graphene as metal-free catalyst and exploration of the roles of various nitrogen states in oxygen reduction reaction

► We design a simple solvothermal method to synthesize amino-functionalized graphene (AG) as metal-free catalyst for oxygen reduction reaction (ORR). ► The amino group in AG makes a great contribution to ORR performance. ► The graphitic and amino N atoms determine the onset potential and electron transfer number in ORR. ► The graphitic and pyridinic N atoms are the key factor to enhance the current density in ORR.