CAREER: Multi-Electron Nickel Redox Cycles for Solar Energy Conversion and Storage

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The successful implementation of solar energy as a renewable energy resource must overcome the critical challenge of improving light to electric energy conversion efficiency as well as the development of grid-scale energy storage technologies. Dye-sensitized solar cells and redox flow batteries are two promising technologies which could meet these challenges. Importantly, both devices make use of small molecules to facilitate energy conversion and energy storage. In this project, Dr. Farnum of Auburn University is developing chemical compounds derived from inexpensive, earth-abundant metals capable of storing two electrons per molecule. The ability to store more than one electron at a time, results in increased energy storage density (smaller batteries with longer life). Furthermore, the molecules are designed to enable large voltages to be produced, which can lead to improved power. Dr. Farnum's increases student interest in renewable energy conversion and storage through active outreach efforts to the local community. His activities include science demonstrations to middle-schoolers, battery experimentation with high-schoolers, and collaborative summer research projects with undergraduates from local colleges and universities. With funding from the Chemical Structure, Dynamics, and Mechanisms-B Program of the Chemistry Division, Dr. Farnum of Auburn University is developing mechanistic understanding of multi-electron redox reactions at mono-metallic, nickel-based coordination compounds. His work specifically focuses on 4-coodinate nickel (Ni(II)) complexes which undergo two-electron redox chemistry to generate 6-coordinate Ni(IV). These studies are inspired by the demand for higher efficiencies in heterojunction solar cells as well as growing interests in electrochemical energy storage technologies that will allow further implementation of renewable energy resources. The nickel complexes take advantage of distinct changes in coordination environment induced upon electron transfer between d8 Ni(II) and d6 Ni(IV) metal centers. Detailed mechanistic analysis of this redox cycle using electrochemical, spectroscopic, and computational methods may result in a thorough understanding of mechanisms for interconversion between Ni(II) and Ni(IV) oxidation states. Further understanding of these redox couples could lead to increased solar energy conversion in dye-sensitized solar cells and energy storage capacities in redox flow batteries, as well as to new molecular redox couples that take advantage of similar redox cycles. Dr. Farnum is also actively engaged in outreach programs designed to raise awareness of the need for solar energy conversion and storage to the local regions of Alabama and Georgia. Specifically, Dr. Farnum works with Auburn University’s Destination STEM event and Summer Science Institute to engage middle and high school students with interactive learning modules focused on concepts of electrochemical energy storage and energy sustainability. Dr. Farnum also invites undergraduate students from smaller, regional colleges and universities to perform summer research projects in his lab, giving theses students exposure and opportunities to participate in cutting edge research in the conversion and storage of solar energy.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.