Li-air batteries are one of the most promising candidates for rechargeable systems.^[1] Within the context of elucidating the possibilities of aqueous Li-air batteries, developing a cost-effective bifunctional catalyst for oxygen reactions is a key issue. Metal oxides including spinels and perovskites have been shown as efficient catalysts for OER,^[2] while Ag is known as a good catalyst for ORR. We have recently shown that a mixture of Ag particles with Co₃O₄ nanoparticles has superior bifunctional activity than its own components.^[3] Here, we will demonstrate that such effect can also be observed when other support materials than Ag are used. Therefore, this effect could partially be due to a conductivity effect. However, experiments using smooth electrodes suggest that there is a synergistic effect. We will further demonstrate that this effect is also observed for various perovskites loaded on Ag. XPS analysis has shown that the presence of Ag⁺ in contact with Co₃O₄ facilitates the redox switching of Co₃O₄, which might be the reason for the enhanced catalytic activity of the mixture.^[4]

Moreover, the mechanism underlying OER on Co₃O₄ and mixed Ag+Co₃O₄ catalysts is further studied using differential electrochemical mass spectrometry together with ¹⁸O-isotope labelling experiments.^[4-5] The results revealed that the lattice oxygen of the oxide takes part in OER and that the amount of oxygen exchange on the mixed catalyst is larger than that on Co₃O₄. The active surface area is also estimated from these measurements and is compared to that obtained from a simple ball model and BET data.^[6]

Investigation of the catalytic activity of Co₃O₄ catalyst towards oxygen reactions in aprotic electrolytes, namely DMSO, is also presented.

Literature:

[1] K. M. Abraham, Z. Jiang, J. Electrochem. Soc. 1996, 143, 1-5.

[2] A. Bergmann, E. Martinez-Moreno, D. Teschner, P. Chernev, M. Gliech, J. F. de Araújo, T. Reier, H. Dau, P. Strasser, Nature Communications 2015, 6, 8625.

[3] H. M. A. Amin, H. Baltruschat, D. Wittmaier, K. A. Friedrich, Electrochim. Acta 2015, 151, 332-339.

[4] H. Amin, C. J. Bondue, S. Eswara, U. Kaiser, H. Baltruschat, Electrocatalysis 2017, 8, 540-553.

[5] S. Fierro, T. Nagel, H. Baltruschat, C. Comninellis, Electrochem. Commun. 2007, 9, 1969-1974.

[6] H. M. A. Amin, H. Baltruschat, Phys. Chem. Chem. Phys. 2017, 19, 25527-25536.