NSF-BSF: Does Spin Coherence Play a Role in Electrochemical Processes?

With support from the Chemical Structure, Dynamics, and Mechanisms A (CSDM-A) program in the Division of Chemistry, Professor David Waldeck of the University of Pittsburgh, along with Israeli partners Professor Yossi Paltiel of the Hebrew University of Jerusalem and Professor Ron Naaman of the Weizmann Institute, is studying how the spin coherence between electrons affects the outcome of chemical reactions involving the transfer of two electrons. Chemists commonly neglect spin coherence in molecules and describe multi-electron reactions by a series of incoherent, one electron steps. Waldeck, Paltiel, Naaman, and their students will build chiral electrodes to create electron pairs with the specific spin coherence properties for converting a chemical reactant to a particular product state in a simultaneous two electron transfer reaction, rather than two discrete one electron reactions. Their discoveries could lead to new approaches for driving multi-electron redox reactions, which are critical to improving the efficiency of clean energy production and to redox biochemistry. The project will also provide research opportunities for graduate students and postdoctoral scholars. Building on ideas from the chiral-induced spin selectivity (CISS) effect, this project will examine the role of electron spin coherence in chiral matter through a set of experiments that aim 1) to demonstrate the formation of coherent spin-polarized electrons and 2) to explore the importance of spin coherence in two-electron transfer reactions. Nanoscopic chiral electrode interfaces will be used to create currents of entangled electron spins and they will be characterized as a function of temperature and interface thickness through interferometry, weak localization, and spin-polarized transport methods. The effect of spin coherence (entangled spins) as compared to spin-correlation of the electrons will be studied for two-electron reactions (the oxygen reduction reaction, reduction of aromatic molecules, and metal ion reduction). These studies aim to distinguish between coherence transport and scattering models of CISS and to shift our fundamental notions about electrochemical catalysis. The collaboration between the Pittsburgh and Israeli research teams will expand the experimental tools used in CISS to include methods that probe coherence and to probe the importance of CISS in quantum matter. 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.