Novel Electrode Materials Based Zn-Air Batteries for Energy Storage: From Fundamental Aspects to System Engineering

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Metal-air batteries (MAB) and especially zinc-air batteries (ZABs) have attracted much attention as promising electrochemical energy storage techniques because of their high energy density, low cost and high safety. The technical application of ZABs is hindered, however, by basic problems such as (i) the lack of suitable bi-functional oxygen reduction/evolution (ORR/OER) catalysts, possibly combined with novel gas diffusion electrode structures, (ii) dendrite formation during Zn deposition (charging) on the Zn anode, leading to short-circuiting of the ZAB, and (iii) deficits in the mass/heat management of the battery required to sustain a long cycling life. These problems are addressed in the present project by combining the preparation, systematic modification and in situ characterization of realistic bi-functional ORR/OER catalyst materials and of functional zinc anodes with experimental studies of structurally/ chemically well-defined model electrodes and the theoretical description based on density functional theory adapted to an electrochemical environment. Anion or cation doped spinel oxides are proposed as efficient, low cost bi-functional ORR/OER catalysts, as they allow us to vary the chemical properties of the active centers (metal surface ions) in different ways, as required for bi-functional catalysts active for ORR and OER. For an improved gas/liquid mass transport a novel porous gas diffusion electrode will be designed, where the bi-functional catalyst is loaded on a Ni foam whose hydrophobicity is optimized by a hydrophobic polypyrrole film. Zinc dendrite formation at the anode shall be addressed by preparing porous shell confined Zn grains to inhibit the diffusion of Zn2+ ions and by adding specifically adsorbed ions to suppress the growth of Zn dendrites. This will be accompanied by identifying optimized operating conditions and technical electrode structures such as porous oxygen electrodes on the basis of technical simulations, and by optimizing the battery design with respect to mass and heat transport. The results of this strategy will be validated in half-cell measurements and full cell battery tests.