The Chemical Catalysis Program of the Chemistry Division supports the project by Professors Craig A. Grapperhaus and Pawel M. Kozlowski. Professors Grapperhaus and Kozlowski are faculty members of the Department of Chemistry at the University of Louisville. They are developing novel ligand-centered electrocatalysts for the evolution and oxidation of hydrogen. Hydrogen serves as a promising alternative carbon-free fuel and is an essential building block for industrial and agricultural processes. Currently, 95% of industrial hydrogen derives from unsustainable fossil-fuel cracking. The catalysts in this project employ a ligand-centered approach. Ligands are small molecules that bind a central metal into a complex. A major advantage of the ligand-centered approach is that the organic framework functions as the active site, allowing the development of catalysts that are metal-free or promoted by sustainable transition-metals (e.g. copper) or non-transition metals (e.g. zinc). The project facilitates the development of sustainable hydrogen evolution/oxidation systems, which have practical applications. It further strengthens connections between the researchers and the Conn Renewable Energy Center, a center that promotes partnerships among Kentucky's colleges and universities, private industries, and non-profit organizations dedicated to renewable energy solutions. Graduate students and undergraduate participants learn a diverse combination of skills including synthesis, characterization, electrochemistry, and computation. The project is well suited for undergraduate research students, who participate and make contributions on a topic of interest and concern to many young scientists-in-training.
The catalysts in this project are at the forefront of an emerging ligand-centered approach that avoids traditional metal-hydrides, which have been well studied. In contrast, the ligand-centered approach remains underdeveloped, and fundamental questions regarding structure-activity relationships remain to be answered. Symmetric and asymmetric N2S2 bis-thiosemicarbazone catalysts are prepared under three metal loading conditions: 1) transition metal (copper); 2) non-transition metal (zinc); 3) metal-free. The functional groups on the ligands and metal-component are varied to evaluate ligand- and metal effects on catalytic activity. The requisite features required for ligand-centered hydrogen evolution/oxidation are being established through a systematic "trimming" of the bis-thiosemicarbazone framework involving the synthesis of new catalysts based on fragments of the larger ligand. Using insights developed during the project, a third-generation of ligand-centered catalysts are under design as "active site pockets" that position key components in the proper geometric positions to promote activity. The educational plan includes graduate and undergraduate training with an emphasis on minority and first-generation college students.
