Homogeneous Solar Hydrogen Photocatalysis: Sensitizer Design and Mechanistic Insights from Transient Spectroscopy

North Carolina State University, Raleigh NC

Investigators

Abstract

In this project funded by the Chemical Catalysis Program of the Chemistry Division, Professor Felix Castellano at North Carolina State University is developing new molecular-based hydrogen-generating systems that function with light and in water. While the chemical process of using light to reduce protons to molecular hydrogen is of fundamental technological importance, only a handful of molecular-based systems can accomplish this important transformation in pure water. This research project directly addresses current themes related to the growing demand for renewable energy sources to power the planet in the future and safeguarding global environmental integrity. Students involved in this project are being cross-trained in numerous areas of chemistry. The proposed investigations are not only fostering the scientific and professional education of undergraduate and graduate students engaged in the project, but also are involving these students in regional public scientific education outreach activities. Professor Castellano is designing new photosensitizers, new classes of electron donors, evaluating the photocatalytic cycle activation pathways (reductive or oxidative electron transfer, triplet energy transfer), and optimizing the compositions of these components to discover the best systems for detailed mechanistic studies using transient spectroscopic methods. The new classes of metal-to-ligand charge transfer sensitizers being synthesizes are based upon water-soluble Ir(III), Ru(II), and Cu(I) complexes. The concept of employing triplet energy transfer shuttles to mediate the initial electron transfer reaction to the requisite cobalt-based water reduction catalyst and/or electron donor species is being studied as well. Performance metrics of these systems are being evaluated in parallel using combinatorial photochemistry, and various analytical approaches are being used to determine the chemical fate of the numerous reaction components and to identify deleterious decomposition pathways. A detailed understanding of the mechanisms of action of the optimized photocatalytic compositions is being gained using a battery of static and dynamic spectroscopic techniques. This interdisciplinary project is contributing to the fundamental knowledge base of converting solar energy into a renewable environmentally friendly, non-carbon-based chemical fuel.