In the effort to develop alternatives to the uneconomic Platinum Group Metal (PGM)-based electrocatalysts for the sluggish oxygen reduction reactions (ORR) in the electrochemical energy conversion and storage systems, graphene-based catalysts showed impressive potential; nitrogen-doped graphene (N-G) is one of the leading candidates. To further improve the catalytic properties, researchers integrated different materials with N-G to achieve a synergetic effect that may result in an efficient and viable catalyst material. Metal-organic frameworks are one such material utilized by researchers because of their unique structural form and physiochemical properties. In this study, we have integrated ZIF-8 with N-G by a Nanoscale High Energy Wet (NHEW) ball milling process to synthesize N-G/MOF. Extensive material characterizations and electrochemical performance tests were performed for the newly synthesized N-G/MOF. Tested in the Rotating Disk Electrode (RDE) system, N-G/MOF showed electrocatalytic performances compatible with the standard 10% Platinum supported on Carbon (Pt/C) catalyst; the obtained ORR current density in the alkaline medium was higher than the 10% Pt/C. Micro and mesoporous structures of ZIF-8, when integrated with N-G, could host a larger number of catalytic active sites and also facilitate a better reactants species transfer for ORR and hence improve the catalytic current density significantly. As material degradation is one of the key concerns for the catalysts, we have investigated the effect of hydrogen peroxide (H2O2) on the N-G/MOF catalyst in both alkaline and acidic mediums as H2O2 is one of the unavoidable reaction intermediates of the ORR and known to degrade the materials in the electrochemical systems drastically by producing highly oxidative species. Our study shows that N-G/MOF can reasonably maintain its catalytic performance after being exposed to H2O2 of a relatively high concentration. The degradation process of the N-G/MOF catalyst by H2O2 was identified, which should be applicable to other graphene-based electrocatalysts. This study revealed a promising aspect of utilizing the metal-organic framework to improve the electrocatalytic properties of graphene-based materials and also shed light on their degradation process.

Metal-organic framework integrated nitrogen-doped graphene (N-G/MOF): A high potential electrocatalyst for the oxygen reduction reaction

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