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

Abstract

Manganese oxides (MnOx) are expected to be highly active catalysts for O2 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 m2 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 ≈ 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. MnO2 coated with reduced graphene oxide has been firstly prepared by step galvanostatic process and shows enhanced catalytic activity and stability for oxygen reduction reaction.