The Role of Microwave Irradiation Temperature on Nitrogen Doping in Metal-Free Graphene Catalysts for an Efficient Oxygen Reduction Reaction in an Alkaline Condition

We reported the synthesis and characterization of metal-free nitrogen-doped graphene catalysts, and demonstrated their efficiency towards ORR in alkaline medium. The influence of varied microwave irradiation temperature on nitrogen doping efficiency in the graphene oxide (GO) catalyst has been investigated. Nitrogen-doped reduced graphene oxide (NrGO) catalysts with varied nitrogen content were synthesized under microwave irradiation temperature at 120-200 degrees C. The catalyst synthesized at 180 degrees C (NrGO-180) has the highest nitrogen content of 9.8 at% with a maximum proportion of pyridinic-N moiety in the graphene structure. The XPS analysis demonstrates the presence of different nitrogen-containing moieties such as pyridinic, pyrrolic and graphitic nitrogen, and their respective composition changes significantly with microwave-irradiation temperature. The linear sweep voltammograms studies demonstrated that NrGO-180 with a maximum amount of pyridinic-N has displayed excellent electrocatalytic activity towards ORR with an E-onset potential similar to 0.89 V (vs RHE) and half- wave potential E-1/2 = 0.72, which is at par with the studied commercial Pt/C (E-onset = 0.93 V, E-1/2 =0.82) and demonstrated 4-electron pathway. The catalyst NrGO-180 with enhanced electrochemical activity has been subjected to durability test of 5,000 potential cycles via LSV. The durability test confirms the superiority of NrGO-180 over commercial Pt/C catalyst under similar condition.