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

Tetravalent Mn based ternary oxides are of interest as they are important electrode materials. Dimagnesium manganate (Mg ₂MnO ₄) 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. Mg ₂MnO ₄ 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 Mg ₂MnO ₄ is an efficient anode material for oxygen evolution reaction with a current density of 14 mA/cm ². The stability of the anode over several cycles of oxidation and reduction is highly encouraging.