Morphology dependent facile synthesis of manganese oxide nanostructures for oxygen reduction reaction.

Abstract The present work demonstrates the morphology dependent synthesis of manganese oxide using simple hydrothermal method just by adjusting the reaction temperature. The structural and morphological studies confirm the formation of manganese oxide with different phases and anisotropic structures of manganese oxide. Interestingly, electrochemical studies exhibit significant oxygen reduction reaction (ORR) kinetics by manganese oxide nanowires with improved onset potential of +0.83 V versus reversible hydrogen electrode (RHE) and current density of 1.75 mA/cm2 in alkaline condition. Among three different morphologies, nanowires show better catalytic activity due to improved diffusion path length and higher aspect ratio. However, all the three samples follow two (2) - electron transfer ORR kinetics, though four electron transfer kinetics has been of great interest for energy conversion applications. Experimental results represent that the reaction temperature plays a key role in forming different shapes and affect the crystal phase and growth process thereby affecting electrochemical properties. Highlights • Different morphologies are obtained in a simple and cost effective one-step hydrothermal method just by adjusting reaction temperature. • The structural analysis confirms that the nanowires as well as nanoflowers consist of mixed phases of Mn 2 O 3 and Mn 3 O 4 , whereas nanoparticle comprise single phase of Mn 3 O 4. • Comparative electrochemical study shows that the manganese oxide nanowires exhibit better ORR activity. [ABSTRACT FROM AUTHOR]