Nickel-cobalt spinel-based oxygen evolution electrode for zinc-air flow battery

Zinc-air flow battery (ZAFB) represents a candidate for safe, cheap and non-toxic stationary energy storage, however, uneven zinc deposition and low efficiency of oxygen reactions on positive electrode still obstruct its commercialization. In our contribution, we address the latter challenge by performance enhancement of electrode for oxygen evolution reaction (OER) from highly alkaline electrolyte. This was achieved by applying a NiCo2O4 electro-catalytic layer onto the selected 3D nickel-based substrates via electrochemically-assisted deposition followed by calcination. The detailed physico-chemical characterization of the electrodes (specific surface area, conductivity, EDS, SEM + EDS, XRD) confirmed spinel structure of the prepared catalyst and its homogeneous deposition over the substrate. The electrochemical characterization of the electrodes was performed in three different set-ups using a complex methodology incl. voltammetry techniques, electrochemical impedance spectroscopy, galvanostatic load and charge-discharge cycling in the developed 3-electrodes 3compartments battery full-cell. For both Ni substrates the deposited NiCo2O4 catalytic layer effectively lowered the OER overpotential due to significantly enlarged specific surface area. This effect was more pronounced for the foam substrate with more compact structure. The developed ZAFB with the optimized OER electrode achieved stable and efficient performance at high current densities of 100 mA cm-2 (which is the highest reported one for cycling experiments) in a broad SoC range (0-80 %) with energy efficiency of 42.1 % and no decay of capacity utilization.