Synthesis and application of nanostructured MCo2O4(M=Co, Ni) for hybrid Li-air batteries

We report the synthesis of MCo2O4 (M=Co, Ni) on Ni-mesh by a simple metal acetate decomposition method. Stability tests of the samples in aqueous acidified LiCl, LiOH and LiTFSI in H2O/DME showed that Co3O4/Ni and Co3O4-PVP/Ni are relatively stable in alkaline and neutral environments, with Co3O4/Ni being relatively more stable. For NiCo2O4/Ni and NiCo2O4-PVP/Ni, the low weight percentage change of cobalt in LiTFSI in H2O/DME suggests that they are mostly stable in this electrolyte. The electrochemical performance of the Li-air cell was evaluated using Li anode and a LAGP ceramic separator with above mentioned electrolytes. Co3O4 showed slightly higher catalytic activity for oxygen reduction reaction (ORR) than for oxygen evolution reaction (OER) for the first three cycles. The cell with LiTFSI in H2O/DME as aqueous catholyte showed that NiCo2O4 is a better catalyst for the OER than for the ORR, while the reverse was observed when LiOH was used as the electrolyte.