Most electrochemical technologies that operate under ambient conditions require ion-conducting polymer electrolytes. These polymers are passive in that electric bias drives ion migration in the thermodynamically favored direction. Recently, my group engineered two important features into passive ion-selective polymers to introduce the active function of photovoltaic action and demonstration of an ionic solar cell. These features were covalent bonding of photoacid dyes to the polymers such that absorption of visible light resulted in liberation of protons, and synthesis of polymer membranes with charge-selective contacts to facilitate separation and collection of H+ and OH–. Light excitation from either side of the polymer membranes resulted in H+ dissociation followed by directional charge collection. The charge collection direction was dictated by the electrostatic asymmetry in the polymers, which was formed due to an external pH difference setup across the membrane.
Joining a monopolar cation-selective polymer to a monopolar anion-selective polymer forms a bipolar membrane, which mimics a rectifying semiconductor pn-junction diode in form and function, and is able to maintain pH differences across it. Using a photoacid-dye-modified bipolar membrane, we measured a photovoltage of ~120 mV under conditions of solar-simulated excitation. In addition to more traditional electrochemical techniques, insights into materials function were obtained using finite-element numerical modeling of photoacid kinetics and membrane physics; beam-line x-ray scattering measurements; electrochemical impedance, solid-state NMR, and pulsed-laser spectroscopies; and fluorescence, electron, and force microscopies. Collectively, these photo-responsive polymers represent a new class of functional materials that use light to trigger changes in local ion concentration and electrostatic potential. These local changes can be used to affect macroscopic processes such as direct sunlight-driven redox chemistry or desalination of salt water, chemical catalysis, and triggering of cellular processes.
- Reiter, R. S.; White, W.; Ardo, S. Journal of The Electrochemical Society, 2016, 163, H3132–H3134. Electrochemical characterization of commercial bipolar membranes under electrolyte conditions relevant to solar fuels technologies.
- White, W.; Sanborn, C. D.; Reiter, R. S.; Fabian, D. M.; Ardo, S. Journal of the American Chemical Society, 2017, 139, 11726–11733. Observation of photovoltaic action from photoacid-modified Nafion due to light-driven ion transport.
- White, W.; Sanborn, C. D.; Fabian, D. M.; Ardo, S. Joule, 2018, 2, 94–109. Conversion of visible light into ionic power using photoacid-dye-sensitized bipolar ion-exchange membranes.
Shane obtained a B.S. Degree in Mathematics, with a minor in Computer Programming, from Towson University and subsequently worked as a software engineer, community college instructor, and high school teacher prior to attending graduate school. Shane obtained an M.S. Degree in Nutrition from the University of Maryland, College Park followed by M.A. and Ph.D. Degrees in Photo-Physical Inorganic Chemistry from the Johns Hopkins University, where he worked for Prof. Jerry Meyer. He then worked for Prof. Nate Lewis as a DOE-EERE Postdoctoral Research Awardee at the California Institute of Technology until 2013. Since that time, Shane has been an Assistant Professor at the University of California, Irvine in the Department of Chemistry and holds a joint appointment in the Department of Chemical Engineering and Materials Science. He leads the Ardo Group for Molecular-Level Engineering of Functional Materials, which designs, synthesizes, and characterizes molecule–materials hybrids and aims to understand and control reaction mechanisms at asymmetric interfaces with the goal of optimizing energy conversion for practical applications, including solar seawater desalination, solar fuels devices, photovoltaics, fuel cells, and batteries. In 2016, Shane was named one of five inaugural Moore Inventor Fellows. He is also a recipient of a DOE Early Career Research Award and a Beall Innovation Award, and was named a Sloan Research Fellow, a Cottrell Scholar, a Kavli Fellow, and a Scialog Fellow. Shane has given over 100 invited talks, including at the National Academy of Sciences Distinctive Voices Lecture Series, the 2017 Resnick Institute Young Investigators Symposium, and Apple’s Membrane R&D Division. His research group is also supported by funding from the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy, the U.S. National Science Foundation’s Chemical Catalysis Program, Nissan Chemical Industries Ltd., and collaborative projects funded by University of California MEXUS–CONACYT and Research Corporation for Science Advancement.