(Invited) Elucidating Oxygen Evolution on Model Oxide Electrodes

Wednesday, 4 October 2017: 14:00
National Harbor 15 (Gaylord National Resort and Convention Center)
I. E. L. Stephens (Technical University of Denmark)
It is particularly challenging to catalyse oxygen evolution under the acidic conditions of polymer electrolyte membrane (PEM) electrolysers. All compounds, apart from IrOx and RuOx, are catalytically inactive or unstable. I will present a series of model studies where we aim to elucidate the factors that control oxygen evolution.

Using thin films of RuO2, we showed that continuous mass losses occur in parallel to oxygen evolution, even when the electrochemical response is stable.1 This finding demonstrates that short term electrochemical measurements are an insufficient measure of long term stability. Our experiments on mass-selected Ru and RuOx particles revealed the high sensitivity of the oxygen evolution performance of nanoparticulate catalysts to the exact oxidation treatment.2,3 X-ray absorption measurements, taken in-operando, provide spectroscopic evidence for the potential dependent coverage of the reaction intermediates. Moreover, tests on oriented thin films indicate that the “coordinatively unsaturated” surface site is responsible for the activity of RuO2.4 Our very recent studies suggest that the dissolution rate of RuO2 is also highly dependent on the orientation.

The scarcity of RuOx and IrOx could limit the scalability of PEM electrolysers. An alternative strategy could be utilise non-precious metal oxides to catalyse oxygen evolution in acid. However, most non-precious metal oxides exhibit poor stability. Theoretical calculations predicted that MnOx could be stabilised against corrosion by the presence of TiOx at its surface, without affecting the catalytic activity. Our experiments on sputter-deposited thin films verify this notion. 5

The catalysts under investigation include model-size selected nanoparticles, commercial high surface area catalysts, sputtered films and oriented thin films. We have probed these surfaces with electrochemical measurements, ultra-high vacuum based surface science methods, electron microscopy, synchrotron-based spectroscopy and density functional theory calculations.

1 Frydendal, R., Paoli, E. A., Knudsen, B. P., Wickman, B., Malacrida, P., Stephens, I. E. L. & Chorkendorff, I. ChemElectroChem 1, 2075, (2014).

2 Paoli, E. A., Masini, F., Frydendal, R., Deiana, D., Malacrida, P., Hansen, T. W., Chorkendorff, I. & Stephens, I. E. L. Catal. Today 262, 57, (2016).

3 Paoli, E. A., Masini, F., Frydendal, R., Deiana, D., Schlaup, C., Malizia, M., Hansen, T. W., Horch, S., Stephens, I. E. L. & Chorkendorff, I. Chemical Science 6, 190, (2015).

4 Stoerzinger, K. A., Diaz-Morales, O., Kolb, M., Rao, R. R., Frydendal, R., Qiao, L., Wang, X. R., Halck, N. B., Rossmeisl, J., Hansen, H. A., Vegge, T., Stephens, I. E. L., Koper, M. T. M. & Shao-Horn, Y. ACS Energy Letters, 876, (2017).

5 Frydendal, R., Paoli, E. A., Chorkendorff, I., Rossmeisl, J. & Stephens, I. E. L. Adv. Energy Mater. 5, 1500991, (2015).