Bifunctional catalytic activity of oxides and perovskites-based catalysts for oxygen reactions: Effect of metal support
Hatem Amin, University of Oxford , Oxford, UKMohammed Soltani, Universität Bonn, Bonn, GermanyChristoph Bondue, Universität Bonn, Bonn, GermanyLingxing Zan, Universität Bonn, Bonn, GermanyBaltruschat Helmut, Universität Bonn, Bonn, Germany
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, 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. 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.
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.[3-4] 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. Co3O4 catalyst was also investigated for oxygen reactions in an aprotic electrolyte (DMSO) for the Li-air battery application.
 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.
 H. M. A. Amin, H. Baltruschat, D. Wittmaier, K. A. Friedrich, Electrochim. Acta 2015, 151, 332-339.
 H. Amin, C. J. Bondue, S. Eswara, U. Kaiser, H. Baltruschat, Electrocatalysis 2017, 8, 540-553.
 S. Fierro, T. Nagel, H. Baltruschat, C. Comninellis, Electrochem. Commun. 2007, 9, 1969-1974.
 H. M. A. Amin, H. Baltruschat, Phys. Chem. Chem. Phys. 2017, 19, 25527-25536.