Direct synthesis of manganese oxide electrocatalysts on carbon nanotubes in supercritical carbon dioxide

Novel method of the direct synthesis of MnO2 on multiwalled carbon nanotubes by thermal decomposition and oxidation of cyclopentadienylmanganese tricarbonyl precursor in supercritical CO2 is proposed. The phase compostion is analysed using X-ray difraction, morphology is studied by means of transmission and scanning electron microscopy. Electrochemistry of the obtained composites in alkaline electrolyte is studied by means of cyclic voltammetry and the activity in oxygen reduction reaction (ORR) is analysed by means of rotating disc electrode technique. Varying precursor concentration during synthesis allows one to control oxide particle dimensions and specific surface area (SSA) of the oxide phase. The resulting composite materials demonstrated improved mass activity (up to 45 A g(-1) at 800 mV relative to RHE) in ORR.