Understanding electrochemical hydrogenation reactions over post-transition metal electrodes: the role of incidental mediators and metastable phases

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

Electrochemistry enables the use of electrical energy to drive chemical reactions. These types of reactions are increasingly interesting due to their compatibility with renewable electricity infrastructure. The reactions occur by interaction of molecules with materials known as electrodes, which are held at an applied voltage and can exhibit catalytic properties when the molecules contact their surfaces. This project will investigate a phenomenon where the electrode material is not static, but instead generates corrosion products that mediate the catalytic reactions. In many cases, corrosion is seen as a detrimental process; however, in this project the investigators aim to use corrosion products purposefully and productively. The mechanism is not yet well understood, and gaining the ability to control and exploit it could have consequences for the design of electrochemical systems for a wide array of chemical production. Specific reactions to be studied in this project relate to the conversion of biomass-derived molecules to make green fuels and chemical precursors to biodegradable plastics. In addition to the expected benefits of Ph.D. training for workforce development, the PIs will establish research opportunities for undergraduates as well as educational materials for larger groups of students, scientists, and non-expert community members. Several of the initiatives to be supported are ongoing, while the project will add a new research experience opportunity for local community college instructors to help in shaping future curriculum and guiding students in continuing from two-year to four-year degree programs. The goal of this project is to understand the extent to which reduced metal species, generated by cathodic corrosion processes such as the formation of dissolved metal hydrides or anions, may mediate reduction of molecules. While traditionally viewed as detrimental side reactions, the project explores the hypothesis that these cathodic corrosion products can mediate homogeneous reduction, even as the primary mechanism in some cases. This hypothesis will be evaluated against possible mechanisms with heterogeneous charge transfer from either the native electrode material or from metastable in-situ phases such as solid metal hydrides or alkali alloys. Specific reactivity studies will involve reduction of levulinic acid (LA) as a testbed. This molecule is derived from renewable biomass and can be electro-reduced to several valuable products. The PIs have obtained preliminary evidence that corrosion-product mediation may be involved on materials that are highly selective to making hydroxyvaleric acid (a monomer for biodegradable plastics) and gamma-valerolactone (a green solvent and biofuel) from LA. The plan is to combine rigorous kinetic measurement tools, quantum chemical calculations, in-situ vibrational and electronic spectroscopy, and a suite of other advanced materials characterization techniques to understand and ultimately leverage the phenomena more broadly into better-controlled electrolysis systems. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.