Investigation of Semiconductor Surfaces and Catalyst Interfaces for Water Oxidation with Solar Energy

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Sunlight is the largest energy resource available on Earth. Harvesting even a small fraction of the sunlight striking the United States would help our country become energy independent. There are several factors which limit full utilization of sunlight to meet our energy needs. For example, sunlight is intermittent while our energy demands are nearly constant. Also, it is difficult to use solar energy directly to meet some of our needs, such as transportation fuels. These factors motivate efforts to convert solar energy into chemical fuels, often referred to as solar fuels. Water is one of the most abundant chemicals available on Earth, and a reaction known as oxidation enables the energy of the sun to convert water into useful forms of energy (electrons and protons). Scientists currently do not fully understand the processes which control solar-powered water oxidation. In this project, Dr. Hamann is investigating the fundamental steps of water oxidation on semiconductor surfaces that absorb sunlight. Catalysts deposited on those surfaces use the absorbed solar energy to oxidize water. Dr. Hamann is also engaged in several outreach activities that leverage his research activities. These activities engage the public and students at all levels in the scientific challenges associated with solar energy capture and conversion to useful forms of energy (like solar fuels). These activities include participation in the Michigan State University Science Festival, a series of Science Café's focused on sustainability, the Midwestern Symposium on Undergraduate Research, and the American Chemical Society (ACS) Project SEED for economically disadvantaged high school students.With funding from the Chemical Catalysis Program of the Chemistry Division, Dr. Hamann of Michigan State University (MSU) is investigating photo-induced water oxidation with metal oxide semiconductors. Surface states, both defect and photo-induced species, play a dominant role in controlling the efficiency of water oxidation on metal oxide semiconductors. A suite of electrochemical, photoelectrochemical, spectroscopic and operando measurements are being carried out to elucidate the nature and behaviour of these surface states during solar water oxidation on ternary metal oxide electrodes, including copper tungstate, CuWO4. Integration of water oxidation catalysts on semiconductor surfaces is a promising method to improve the water oxidation efficiency, however the nature of the interface that develops between semiconductor and catalyst, and its effect on the electron-transfer reactions occurring at this interface, is not well understood. Several semiconductor/catalyst combinations are also being investigated to develop a general and detailed understanding of the role of the interface in controlling the overall water oxidation reaction. The knowledge gained from this research allows the development of efficient conversion of solar energy to high energy density chemical fuels, which is a significant benefit to society. Additional broader impacts of this research derive from Dr. Hamann's outreach and educational activities at all levels. These activities increases interest, understanding and participation of underrepresented minorities in this area of science. Specific outreach efforts include participation in the MSU Science Festival, the Midwestern Symposium on Undergraduate Research, a series of Science Café's focused on sustainability, and the ACS Project SEED.