Investigation of Highly Active Carbon-, Cobalt-, and Noble Metal-Free MnO/NiO/Ni-Based Bifunctional Air Electrodes for Metal-Air Batteries with an Alkaline Electrolyte.

Compared to other battery technologies, metal-air batteries offer high specific capacities because the active material at the cathode side is supplied by ambient atmosphere. To secure and further extend this advantage, the development of highly active and stable bifunctional air electrodes is currently the main challenge that needs to be resolved. Herein, a highly active carbon-, cobalt-, and noble-metal-free MnO/NiO-based bifunctional air electrode is presented for metal-air batteries in alkaline electrolytes. Notably, while electrodes without MnO reveal stable current densities over 100 cyclic voltammetry cycles, MnO containing samples show a superior initial activity and an elevated open circuit potential. Along this line, the partial substitution of MnO by NiO drastically increases the cycling stability of the electrode. X-ray diffractograms, scanning electron microscopy images, and energy-dispersive X-ray spectra are obtained before and after cycling to investigate structural changes of the hot-pressed electrodes. XRD results suggest that MnO is dissolved or transformed into an amorphous phase during cycling. Furthermore, SEM micrographs show that the porous structure of a MnO and NiO containing electrode is not maintained during cycling.