(638b) Investigation of Surface Oxidation State and Oxygen Evolution Activity of Manganese Oxide Nanoparticles

The oxygen evolution reaction (OER) is a key energy conversion reaction in a number of clean energy technologies, including rechargeable metal-air batteries, electrolysis cells, and solar fuel synthesis. Widespread commercialization of these technologies is desirable but limited by the scarcity and high cost of the best known catalysts for OER, ruthenium and iridium oxides.¹ In search of replacements for these active precious metal oxides, recent research has focused on earth-abundant catalysts such as manganese oxides (MnO_x)^2-4 and cobalt oxides.^5-7 Interestingly, OER on both manganese and cobalt oxides has been shown to vary with the nature of underlying support, but the possible effect of the support on the oxidation state of the oxide and the corresponding catalytic activity has not yet been determined.^4,6

In our work, we prepare MnO_x nanoparticles on a variety of supports and characterize the oxidation state of Mn using ex-situ L-edge X-ray absorption spectroscopy both before and after catalysis. We find that the support has an effect on both the initial oxidation state of Mn and the extent of the oxidation of Mn after the application of OER relevant potentials. Characterization of OER activity of MnO_x nanoparticles reveals that supports which favor incomplete oxidation of MnO_x nanoparticles to a mixed Mn (III, IV) oxide phase produce a more active OER catalyst than supports which favor oxidation of MnO_x nanoparticles to MnO₂.

References

1. Trasatti S. Electrocatalysis in the anodic evolution of oxygen and chlorine. Electrochimica Acta. Received May 15, 1984 1984;29(11):1503-1512. 2. Jiao F, Frei H. Nanostructured manganese oxide clusters supported on mesoporous silica as efficient oxygen-evolving catalysts. Chemical Communications. 2010;46(17):2920-2922. 3. Gorlin Y, Jaramillo TF. A Bifunctional Nonprecious Metal Catalyst for Oxygen Reduction and Water Oxidation. J. Am. Chem. Soc. Oct 2010;132(39):13612-13614. 4. El-Deab MS, Awad MI, Mohammad AM, Ohsaka T. Enhanced water electrolysis: Electrocatalytic generation of oxygen gas at manganese oxide nanorods modified electrodes. Electrochem. Commun. Aug 2007;9(8):2082-2087. 5. Frei H. Polynuclear Photocatalysts in Nanoporous Silica for Artificial Photosynthesis. Chimia. 2009;63(11):721-730. 6. Yeo BS, Bell AT. Enhanced Activity of Gold-Supported Cobalt Oxide for the Electrochemical Evolution of Oxygen. J. Am. Chem. Soc. Apr 2011;133(14):5587-5593. 7. Kanan MW, Nocera DG. In situ formation of an oxygen-evolving catalyst in neutral water containing phosphate and Co2+. Science. Aug 2008;321(5892):1072-1075.