Oxygen Reduction Properties of Bifunctional α-Manganese Oxide Electrocatalysts in Aqueous and Organic Electrolytes

Several different preparation and morphologies of alpha-manganese oxide catalysts: were synthesized, and their physical properties were :charaterized. These catalysts were also characterized by electrochemical means (RDV and CV) for oxygen reduction in both aqueous and organic electrolytes : The solvent-free preparation yielded catalysts with ideal physical properties: low average oxidation state. (3.73) of manganese, small crystallite size (8.1 nm), small particle size (d = 10 nm, l = 30-100 nm), high surface area (144 m(2) g(-1)), and pore volume (0.470 cm(3)/g). This catalyst displayed the highest activity in both aqueous (i(L) = 3.66 +/- 0.12 mA cm(-2), i(0) = 1.0 x 10(-5) mA cm(-2)) and organic electrolytes (i(L) = 2.25 +/- 0.15 mA cm(-2), an = 0.51). Doping the solvent-free preparation with Ni(2+) slightly improved its oxygen reduction capabilities in aqueous (i(L) = 3.78 +/- 0.15 mA cm(-2), i(0) = 2.3 x 10(-5) mA cm-(2)) and organic electrolytes(i(L) = 2.43 +/- 0.17 mA cm(-2), an = 0.47). A large increase in the ability of the catalysts to decompose hydrogen peroxide was observed (2.7 +/- 0.26 vs 0.53 +/- 0.03 s(-1) g(-1)), which is a good indicator of enhanced bifunctionality for application in secondary lithium air batteries. Stability tests in the presence of L(i)O(2) at elevated temperatures (100 degrees C) indicate a decrease in catalyst crystallinity as exposure time is increased.