(4ey) Synthesizing and Optimizing Manganese Dioxide Nanorods and Its Behavior Toward Oxygenreduction Reaction

Alkaline membrane fuel cell (AMFC) is an electrochemical conversion device, which produces electrical energy
through oxygen reduction reaction. Platinum metal has been used as a catalyst since its inception, but expansiveness
and low stability at alkaline medium are the major obstacles in its commercialization. Manganese dioxide (MnO2)
has been used for various energy and environmental applications; however the thermal sensitive MnO2 has not been
studies yet. Based on metal cost α-MnO2 has higher specific activity as compared to commercial Pt/C catalyst, thus
considered to be potential cathode material for AMFCs. Herein α-MnO2 nanorods have been produced by treating
MnO2 under different temperature (300, 400 and 500 0C) and their physical and electrochemical properties were
explored. By providing optimum gas pressure the oxygen vacancies were induced thermally in the α-MnO2
nanorods. Oxygen vacancies of α-MnO2 nanorods were explored by high-angle angular dark field (HAADF). It was
also found from X-ray photoelectron spectroscopy (XPS) analysis that oxygen vacancies were more strengthened
with increasing temperature. The samples were investigated for oxygen reduction reaction (ORR), it was found that
sample treated at 400 0C has the excellent ORR performance, higher long term stability in alkaline medium and best
methanol tolerance as compared to commercial Pt/C. these properties have been imparted to the catalyst due to
preferential growth of catalyst at (211) plane and optimized oxygen vacancies creation. The α-MnO2 nanorods
became longer and thinner with increasing temperature and it was believed that this was another reason for better
performance. This work implied that α-MnO2 nanorods are temperature sensitive and best ORR performance can be
achieved by optimizing calcination temperature.

Keywords: Alkaline membrane fuel cell, manganese dioxide catalyst, oxygen reduction reaction, nanorods, oxygen
vacancies.