MnO2 coated with graphene by galvanostatic electrodeposition and its enhanced electrocatalysis for oxygen reduction

Manganese oxides (MnOx) are expected to be highly active catalysts for O-2 electroreduction. However, MnOx are prone to aggregation, thus reducing their catalytic active sites. Herein, a composite of spherical MnO2 coated with reduced graphene oxide (denoted as MnO2@RGO) was fabricated by a facile and green step galvanostatic electrodeposition. The obtained MnO2@RGO is composed of a RGO lamina shell (10 nm) and spherical MnO2 core (100 nm), which were confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunner-Emmet-Teller (BET) measurement, Raman, and X-ray photoelectron spectroscopy (XPS). The obtained composite exhibited a high specific surface area of 251.3 m(2) g(-1). The as-prepared MnO2@RGO composite displayed a more positive onset potential of 0.86 V vs. reversible hydrogen electrode (RHE), higher kinetic current density (11.23 mA cm(-2) at 0.2 V), and higher electron transfer number in OH- solution (n approximate to 3.94) for oxygen reduction reaction (ORR) compared to MnO2 NPs scattered on the surface of RGO (MnO2/RGO), bulk MnO2 NPs, and RGO. The enhanced activity was further demonstrated by the lower Tafel slope (72 mV dec(-1)). Moreover, MnO2@RGO exhibited greater tolerance to methanol, anti-CO poisoning ability, and catalytic stability compared to commercial Pt/C catalyst. The results indicated that the prepared MnO2@RGO composite can be a potential low-cost and effective electrocatalyst for ORR. [GRAPHICS] .