Spinel-type oxides LiMn2−xMxO4 [M=Co, Fe, (CoFe)] as electrocatalyst for oxygen evolution/reduction in alkaline solution

The secondary metal±air battery is an attractive power source due to its high speci®c energy [1], but it is not used widely because there is a lack of an ideal electrocatalyst for the bifunctional air electrode. Such an electrocatalyst must possess high activity, low price and be stable in alkaline solution [2, 3]. Basically, electrocatalysts with large speci®c surface areas are necessary to obtain high activity [3±5]. Some spinel-type oxides [6± 8] show promise as good electrocatalysts for the bifunctional air electrode because of their high activity for oxygen evolution in alkaline solution. Spinel-type oxides LiMn2yxMxO4 (M=3d metal) have been examined as cathode materials for lithium batteries and rechargeable lithium ion batteries [9±12]. In a previous paper [13], we reported that LiMn2yxCoxO4 (x ˆ 1:0, 1.2, 1.4, 1.6) showed good electrocatalytic activity in 7 M KOH solution. In this study, three series of spinel-type complex oxides LiMn2yxCoxO4 (A series, x ˆ 0, 0.2, 0.4, 0.6, 0.8) LiMn2yxFexO4 (B series, x ˆ 0:2, 0.4, 0.6, 0.8) and LiMn2yxCox=2Fex=2O4 (C series, x ˆ 0:2, 0.4, 0.6, 0.8) have been synthesized by an improved amorphous citric precursor method (IACP), and their electrocatalytic performance has been evaluated in gas-diffusion oxygen electrodes.