Investigation of Highly Active Carbon-, Cobalt-, and Noble Metal-Free MnO2/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 MnO2/NiO-based bifunctional air electrode is presented for metal-air batteries in alkaline electrolytes. Notably, while electrodes without MnO2 reveal stable current densities over 100 cyclic voltammetry cycles, MnO2 containing samples show a superior initial activity and an elevated open circuit potential. Along this line, the partial substitution of MnO2 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 MnO2 is dissolved or transformed into an amorphous phase during cycling. Furthermore, SEM micrographs show that the porous structure of a MnO2 and NiO containing electrode is not maintained during cycling.

Simple Methods for the Preparation of Non-noble Metal Bulk-electrodes for Electrocatalytic Applications.

The rock material pentlandite with the composition Fe4.5Ni4.5S8 was synthesized via high temperature synthesis from the elements. The structure and composition of the material was characterized via powder X-ray diffraction (PXRD), Mössbauer spectroscopy (MB), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and energy dispersive X-ray spectroscopy (EDX). Two preparation methods of pentlandite bulk electrodes are presented. In the first approach a piece of synthetic pentlandite rock is directly contacted via a wire ferrule. The second approach utilizes pentlandite pellets, pressed from finely ground powder, which is immobilized in a Teflon casing. Both electrodes, whilst being prepared by an additive-free method, reveal high durability during electrocatalytic conversions in comparison to common drop-coating methods. We herein showcase the striking performance of such electrodes to accomplish the hydrogen evolution reaction (HER) and present a standardized method to evaluate the electrocatalytic performance by electrochemical and gas chromatographic methods. Furthermore, we report stability tests via potentiostatic methods at an overpotential of 0.6 V to explore the material limitations of the electrodes during electrolysis under industrial relevant conditions.