(483f) Spectroscopic Insight into the Reactivity of Oxide Electrocatalysts with Water

Authors: 
Stoerzinger, K. A., Pacific Northwest National Laboratory
Du, Y., Pacific Northwest National Laboratory
Chambers, S. A., Pacific Northwest National Laboratory
The intermittent nature of renewable energy sources requires storing and converting energy in a clean, scalable way. Water electrolysis and hydrogen fuel cells present a promising solution, however often require precious metals to reduce the kinetic overpotential required for the oxygen evolution and reduction reactions (OER and ORR), which limit the overall efficiency. In alkaline environments, transition metal oxides present an alternative to noble metals for oxygen electrocatalysis. However, a lack of fundamental understanding of the reaction mechanism has hindered their rational design.

Investigation of model epitaxial oxide thin films allows spectroscopic examinations of their chemical speciation in an aqueous environment using ambient pressure X-ray photoelectron spectroscopy.1 By quantifying the formation of hydroxyl groups, we compare the relative affinity of different surfaces for this key reaction intermediate in oxygen electrocatalysis.2 The coverage of hydroxyl groups measured spectroscopically at a fixed relative humidity trends with the free energy of a hydroxylated surface calculated by density functional theory, providing an experimental handle on the binding strength of this reaction intermediate.3 Understanding the electronic structure of oxides in an aqueous environment is also critical for promoting charge transfer reactions in both electrocatalytic and photocatalytic reactions. To this end, we investigate changes in the electronic structure as a function of the oxygen and water chemical potential, enabling comparison with the metal redox potential and catalytic activity. The understanding developed from epitaxial surfaces builds molecular insight regarding interactions at oxide/water interfaces, and guides the rational design of high-surface-area oxide catalysts for technical applications.

References

1. K.A. Stoerzinger, W.T. Hong, E.J. Crumlin, H. Bluhm, and Y. Shao-Horn, Accounts of Chemical Research, 48, 2976 (2015).

2. K.A. Stoerzinger,R. Comes,S.R. Spurgeon, S. Thevuthasan, K. Ihm,E.J. Crumlin, S.A. Chambers. J. Phys. Chem. Lett. 8, 1038 (2017).

3. K.A. Stoerzinger, W.T. Hong, G. Azimi, L. Giordano, Y.-L. Lee, E.J. Crumlin, M.D. Biegalski, H. Bluhm, K.K. Varanasi, Y. Shao-Horn. J. Phys. Chem. C 119, 18504 (2015).