In aqueous electrolytes, oxides are the best bifunctional electrode materials. We have recently shown that the activity of silver for oxygen reduction is increased when Ag particles are in contact with Co3O4 particles. Also, the activity of Co3O4 for oxygen evolution is increased in such a mixed catalyst. [4] We will demonstrate here that to some extent such effects can also be observed when other support materials instead of silver are used, therefore, part of the effect may be due to conductivity effects. However, model experiments using smooth electrodes demonstrate that there is also a true synergistic effect between Ag and the Co-oxide. We will further demonstrate that this effect is also observed for various perovskites mixed with or deposited onto 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.[5]
Using differential electrochemical mass spectrometry (DEMS) and 18O- isotope labeling it has been shown that the lattice oxygen is participating in the OER at oxides.[6-9] This procedure is applied to Co3O4 and the mixed catalyst as well. The active area thus determined will be compared to that estimated from BET data and a simple ball model.
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[3] P. Reinsberg, C.J. Bondue, H. Baltruschat, J. Phys. Chem. C 120 (2016) 22179-22185.
[4] H.M.A. Amin, H. Baltruschat, D. Wittmaier, K.A. Friedrich, Electrochimica Acta 151 (2015) 332-339.
[5] H.M. Amin, C.J. Bondue, S. Eswara, U. Kaiser, H. Baltruschat, Electrocatalysis 8 (2017) 540-553.
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[8] K. Macounova, M. Makarova, P. Krtil, Electrochemistry Communications 11 (2009) 1865-1868.
[9] H.M.A. Amin, H. Baltruschat, Phys. Chem. Chem. Phys. 19 (2017) 25527-25536.