Non-noble Metal Manganese Achored On Graphene As Catalyst For Oxygen Reduction Reaction

In recent years, increasing energy and environmental concerns about the negative effect of fossil fuels to the environment have stimulated extensive research on various renewable energy storage and conversion techniques such as metal–air batteries, CO₂ capture, water splitting, and fuel cells. Among these techniques, considerable research attention has been focused on fuel cells because of their distinctive advantages, such as high efficiency, large specific energy density, and low pollution. However the key procedure for fuel cell is involved in electrochemical reactions: oxygen reduction reaction（ORR）. One of the major challenges is enhancing the activity of anodic catalysts for fuel’s oxidation and catalysts toward oxygen reduction reaction. In this paper, on the basis of the previous research of the electrocatalyst for ORR, we have prepared several different non-noble metal ORR catalysts（Mn O₂/r GN、Mn₃O₄/r GO、MG-15）. The specific characterization and discussion were summarized as following.（1） Mn O₂/N-doped graphene composite was synthesized via a facile hydrothermal reaction using KMn O4 as manganese source and graphene oxide as carbon source. The as-prepared electrocatalysts of oxygen reduction reaction（ORR） were characterized through X-ray diffraction, Raman spectra, X-ray photoelectron spectra, scanning electron microscopy, and electrochemical measurements. Mn O₂/r GN exhibited optimized catalytic performance compared with Mn O₂ and N-doped graphene（r GN） when tested as ORR electrocatalysts. Remarkably, the excellent durability and tolerance of Mn O₂/r GN to methanol were also better than those of commercial catalyst（20 wt% Pt/C）. Moreover, results indicate that the ORR performance of hybrid materials can be correlated to the synergistic effect of Mn O₂ nanocrystals and N-doped graphene.（2） The composite of manganese oxide nanoparticle supported on reduced graphene oxide（Mn₃O₄/r GO） was synthesized via a simple circulation reflux method withoxide graphene and Mn Cl2·4H2O as precursors. The Mn₃O₄/r GO sample exhibited high ORR activity with a positive onset potential of-0.12 V（vs. SCE） and high limiting current of 4 m A/cm2（close to that of 20% Pt/C,-0.09 V; 3.9 m A/cm2）. Moreover, the durability and tolerance to methanol of as-prepared products are good compared with commercial 20% Pt/C. The results showed that Mn₃O₄ supported on r GO displays promising stability characteristics for applications as oxygen catalysts.（3） In this part, we report a highly active hybrid Mn₃O₄ nanoparticles-reduced graphene oxide（MG-15） oxygen reduction reaction electrocatalyst, prepared through one-step microwave-assisted synthetic route. The Raman spectroscopy and X-ray diffraction（XRD） measurements confirm the reduction of GO and growth of nanosized Mn₃O₄. The SEM profile reveals that Mn₃O₄ nanoparticles are randomly distributed evenly on the reduced graphene oxide sheets. The electrocatalytic performance of hybrid material is superior to the r GO and Mn₃O₄ nanoparticles, which indicates that the synergistic effect of Mn₃O₄ and r GO enhances the overall performance of the hybrid catalyst. The mechanism analysis showed that it favors the 4-electron pathway for the reduction of oxygen. The oxygen reduction peak of the MG-15 catalyst in a 0.1 M KOH solution was tested at-0.15 V, which is more positive than 20% Pt/C. The hybrid material shows an onset potential of-0.12 V, which is 180-250 m V more positive than other samples. Furthermore, the MG-15 exhibit excellent electrochemical performance in terms of activity, methanol tolerance and durability...