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

• MnO2 nanorod adsorbed with supports (non-support, carbon black, and MWCNT) is prepared.
• Structures between nanorod and MWCNT are parallel, cross and bend intersect.
• The MnO2/MWCNTs possess good ORR performance and durability.
• The magnesium–air cell of MnO2/MWCNTs has excellent discharge performance and stability.

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 °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.