Preparation of nickel aluminum-manganese spinel oxides NixAl1-xMn2O4 for oxygen electrocatalysis in alkaline medium: Comparison of properties stemming from different preparation methods

Two different procedures were used to prepare spinel-type NixAl1-xMn2O4 (0 less than or equal to x less than or equal to 1) compounds to study the eff ects of solid state properties of mixed oxides on their electrocatalytic pr operties, The oxalic route, coprecipitation of metal oxalates dissolved in propanol or ethanol, and the propionic route, hydrolysis of metal carboxyla tes in propionic acid, have been used, In both routes, thermal decompositio n produces the corresponding oxides. X-ray diffraction patterns showed that the oxides crystallize in a;cubic spinel phase with a unit cell parameter a that increases as aluminum is replaced by nickel. At low x values, compou nds prepared by the propionic route showed a larger variation for parameter a than compounds prepared by the oxalic route, probably due to oxygen stoi chiometric deficiency, This effect was estimated from the tetrahedral force constant (k(t)) values, which showed a fast decrease as x varied from 0 to 1, Electrical conductivity, conduction activation energy, hole mobility, a nd pHz of oxides prepared by the propionic route were also higher than thos e from oxides prepared by the oxalic route. Crystallinity grade and particl e size were nearly 50% higher in propionic-route samples than in oxalic-rou te samples, The apparent and real electrocatalytic activities of both types of oxides were compared for O-2 evolution. (C) 1999 Academic Press.