Preparation of carbon-supported perovskite-type oxides LaMn _1-y,Fe_yO_3+δ based on reverse homogeneous precipitation method

Reverse homogeneous precipitation (RHP) method was successfully applied for dispersing perovskite type oxides LaMn_1-yFe_yO _3+δ (y = 0 - 0.8) finely on carbon support. Mixing the colloidal particles of about 10 nm in size obtained by RHP method with a 2-propanol dispersion of carbon black resulted in precipitation of a precursor/carbon composite, which was further converted into a LaMn _1-yFe_yO_3+δ oxide/carbon composite by calcination. Microscopic observation revealed that nano-sized oxide particles were dispersed fairly well in the carbon support. When applied to gas diffusion-type electrodes, the 30 mass % LaMnO_3+δ/carbon composite thus prepared showed far more excellent oxygen reduction activity than the 50 mass % LaMnO_3+δ/carbon composite conventionally prepared by mechanical mixing. The electrode gave current density as high as 300 mA cm^-2 at -110 mV (vs. Hg/HgO) in 8 M KOH at 60°C under air flow. Oxygen reduction activity of the LaMn_1-yFe_yO _3+δ/carbon composites decreased with increasing y, though the composite at y = 0.4 was still more active than the LaMnO_3.15 composite prepared conventionally by traditional way.