The work will address photocatalytic reduction of carbon dioxide, which is an exciting reaction system with the ability to convert an abundant greenhouse gas to combustible hydrocarbon fuels using sunlight. The proposed study will enable increased efficiency in carbon dioxide photoreduction through fundamental understanding of the photocatalytic reaction mechanisms. Direct solar-to-electrical energy conversion has reached very high efficiencies and low enough costs to compete with combustion of fossil fuels. As such, large scale implementation of gigawatt solar power plants have now become a reality. The main problem that remains, however, is that currently there is no way of storing this large amount of electricity for use during the night, winter months, or cloudy days, when the sun is not shining. Photocatalysis provides a way to store the sun's energy in chemical bonds that can later be released in a carbon neutral cycle.
Specifically, the proposal is aimed at developing a fundamental understanding of photocatalytic processes on novel photocatalysts based on TiO2-passivated III-V compound semiconductors. Here, photocorrosion of the III-V compound surfaces is prevented by the TiO2 passivation layer. In order to establish the extent of photochemical robustness, the study will evaluate the stability of these photocatalysts over weeks and months for a wide range of TiO2 thicknesses and deposition conditions. The study will also investigate the reaction intermediates obtained in non-aqueous (and partially-aqueous) ionic liquid electrolytes (e.g., [EMIM]BF4), which suppress the formation of hydrogen, reduce the energy of the reaction intermediates, and enable the application of higher overpotentials. To separate the effects of the semiconductor substrate from the photoexcited carriers in the metal nanoparticles, experiments will also be carried out utilizing metal nanoparticles on non-semiconducting substrates, such as monolayer graphene.
The principal investigators will also continue and expand educational and outreach activities in the Los Angeles and southern California area, including workshops for high school teachers from disadvantaged schools with added participation by their students, and with the development of photocatalysis related lab kits and demo units that will be given to the teachers to take back to their classrooms.
