(66f) Using in Situ X-Ray Absorption Spectroscopy to Study the Electronic Structure of Manganese Oxide with Gold for the Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is the complementary half-reaction to a number of electrochemical processes, which when combined with a renewable energy source such as wind or solar, are promising methods to produce carbon-neutral fuels. Specifically for the case of water-splitting, the efficiency of this reaction is severely limited by the high overpotential required for the OER, making the development of improved catalysts for the OER a crucial step for advancing hydrogen technology. In order to develop active nonprecious metal-based electrocatalysts for the OER, a better understanding of the activity of transition metal catalysts is needed. Previous studies have shown that depositing transition metal catalysts on metal supports leads to stabilization of different oxide phases and significantly higher activities.^[1,2]

In this work we investigate the interaction between manganese oxide (MnO_x) and noble metals to determine the effect on oxidation state and catalytic activity. Focusing on a study of the interaction between MnO_x with gold (Au), we first characterize the catalyst using SEM and ex situ L-edge x-ray absorption spectroscopy (XAS) to determine the morphology and oxidation state.^[3] As a surface sensitive technique, ex situ XAS provides information on the oxidation state of the surface atoms of the MnO_x nanoparticles both alone and in the presence of Au. Electrochemical characterization of this system shows that adding Au to MnO_x greatly increases the activity for the OER and results in an order of magnitude higher turnover frequency compared to MnO_x without Au. Next, a series of in situ XAS studies on a size-selected MnO_x nanoparticle system provide further insight into the electronic structure of the MnO_x both with and without Au under OER operating conditions. Expanding this study to characterize the interaction of MnO_x with other noble metals elucidates trends with respect to the effect on OER activity.

REFERENCES:
1. Yeo, B.S. & Bell, A.T. Enhanced Activity of Gold-Supported Cobalt Oxide for the Electrochemical Evolution of Oxygen. J Am Chem Soc 133, 5587-5593 (2011).
2. Yeo, B.S. & Bell, A.T. In Situ Raman Study of Nickel Oxide and Gold-Supported Nickel Oxide Catalysts for the Electrochemical Evolution of Oxygen. The Journal of Physical Chemistry C 116, 8394-8400 (2012).
3. Gorlin, Y. et al. Understanding Interactions between Manganese Oxide and Gold That Lead to Enhanced Activity for Electrocatalytic Water Oxidation. J Am Chem Soc 136 (2014).