MnO2 nanorod catalysts for magnesium air fuel cells: Influence of different supports

MnO2 nanorods adsorbed with different supports (non-support, carbon black, and MWCNTs) were prepared through hydrothermal method for magnesium-air fuel cells (MAFCs). The morphological characteristics of the catalysts indicate that the combination modes of nanorods and MWCNTs are parallel, cross, and bend intersect, which provide a large surface areas and enhance electron transfer process. X-ray diffraction pattern illustrates the crystal form of MnO2, and X-ray photoelectron spectroscopy reveals that the existing form of manganese is Mn4+. The ORR performance investigated using a rotating disk electrode shows that the initial reduction potential of MnO2/C and MnO2/MWCNTs in the LSV curves are -0.02 and 0.03 V vs. Hg/HgO (+0.098 V vs. NHE), respectively. The electron transfer number of MnO2/MWCNTs is 3.86, which corresponds to four electrons. In the I-t curves, the oxygen reduction current density of MnO2/MWCNTs decreases by 18.1% and MnO2/C decays by 27.9% after 60 h. The CVs reveal that the current density losses of MnO2/MWCNTs and MnO2/C are 0.4 and 0.8 mA cm(-2) after scanning for 5000 cycles. The potential values of the air electrode loaded with MnO2/C and MnO2/MWCNTs catalysts are -0.78 and -0.62 V vs. SCE, respectively, at 150 mA cm(-2), respectively. The discharge performance of a single-chamber MAFC shows that the peak power densities of MnO2/C and MnO2/MWCNTs are 60.95 and 70.47 mW cm(-2), respectively, 20 degrees C in 10 wt% NaCl solutions. The single cells of MnO2/MWCNTs can continuously discharge for more than 24 h at a current density of 20 mA cm(-2). The EIS proves that the conductivity of MnO2/MWCNTs is higher than MnO2/C. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.