MnO2 nanowires anchored on mesoporous graphitic carbon nitride (MnO2@mpg-C3N4) as a highly efficient electrocatalyst for the oxygen evolution reaction

Abstract

In the present study, we report the rational design and fabrication of a novel nano composite, namely one-dimensional (1D) MnO2 nanowires grew up in situ within the 2D mesoporous carbon nitride (MnO2@mpg-C3N4), as a highly efficient electrocatalyst for OER. The structural, morphological and thermal properties of as-prepared MnO2@mpg-C3N4 electrocatalyst were characterized by TEM, SEM, XRD, XPS, Raman, ICP-MS, and TGA. The results clearly revealed the formation of 3D-hierarchical heterostructures consisting of 1D MnO2 nanowires anchored on mpg-C3N4. Next, the electrocatalytic performance of MnO2@mpg-C3N4 nanocomposite was tested in OER wherein it exhibited substantially enhanced activity than pristine 1D MnO2 nanowires. In particular, the turnover frequency (TOF) of MnO2@mpg-C3N4 (0.84 s(-1)@480 mV) was found almost three times higher than that of ID MnO2 nanowires (0.32 s(-1)@480 mV). Moreover, the overpotential and Tafel slope values were successfully lowered down by using MnO2@mpg-C3N4 nanocomposite compared to those of 1D MnO2 nanowires. It was experimentally demonstrated that the superior OER performance of the MnO2@mpg-C3N4 is attributed to the effective stabilization of Mn3+ species (Mn2O3) in the electrocatalyst via the help of nitrogen functional groups of mpg-C3N4 and the formation of 3D heterostructure that offers the following three major contributions; i) enhanced aerophobicity due to orientation modifications of growing 1D MnO2 nanowires, ii) open structure facilitating the rapid detachment of gas bubbles from the electrode surface, iii) a large number of transport channels for the penetration of electrolyte, ions and electrons.