Nanostructured dimagnesium manganese oxide (Spinel): control of size, shape and their magnetic and electro catalytic properties

Abstract

Tetravalent Mn based ternary oxides are of interest as they are important electrode materials. Dimagnesium manganate (Mg₂MnO₄) is one Mn(IV) containing oxide which has been of interest. Nanostructures of the above oxide (spinel) have been obtained by the thermal decomposition of nanostructured metal oxalate precursor at 500 °C. The size and anisotropy of the oxide nanostructures was controlled by choosing appropriate decomposition temperature of the oxalate precursor. Mg₂MnO₄ nanorods were obtained at low temperature (500 °C), formed by aligned nanoparticles of size∼8–10 nm. These nanoparticles show Curie–Weiss behavior with Weiss constant (14 K). Below ∼50 K there is a small deviation resulting in a negative Weiss constant (−7.36 K) indicating exchange cross over (from ferromagnetic like interactions to antiferromagnetic interactions). The high temperature magnetic moment corresponds to Mn (IV). Electrochemical experiments show that nanostructured Mg₂MnO₄ is an efficient anode material for oxygen evolution reaction with a current density of 14 mA/cm². The stability of the anode over several cycles of oxidation and reduction is highly encouraging.