22^nd International Conference on Past and Present Research Systems on Green Chemistry April 26-27, 2019 Vancouver, British Columbia, Canada

Biography:

Lingzi Sang obtained her B.S. degree in Chemistry from Xiamen University (Xiamen, China) in 2009. She went on to the University of Arizona and obtained her Ph.D. in 2015. During this period, she developed molecular understandings associated to charge transfer efficiencies at the critical interfaces in organic photoelectronic devices. She then moved to Champaign-Urbana for her postdoctoral research at the University of Illinois under the supervision of Prof. Andrew A. Gewirth and Prof. Ralph G. Nuzzo. There she worked on multidisciplinary measurements at electrode and electrolyte interfaces in all-solid lithium ion batteries and unraveled molecular level origins that responsible to battery shorting and capacity fade. Lingzi joined the University of Alberta as an Assistant Professor Aug. 2018. The Sang research group focus on electrochemistry and spectroscopy measurements at critical interfaces in solid state energy conversion and storage systems.

Abstract:

The long-lasting environmental concerns arising from the use of fossil fuels and the rapid growth of renewable energy demand requires safe, large-scale, and reliable nextgeneration energy storage systems. All-solid-state lithium-ion batteries potentially offer enhanced energy and power density, and improved battery safety compared to the liquid electrolyte-based Li-ion batteries that are currently in use. Solid lithium-ion conductors such as thiophosphates are potential electrolyte materials for all-solid Li batteries because of their high Li+ ion conductivity, which is close to its liquid counterparts. Current challenges to achieving high performance all-solid-state batteries with long cycle life include shorting resulting predominantly from Li dendrite formation and infiltration through the solid electrolyte (SE), and increases in cell impedance induced by SE decomposition at the SE/electrode interface. In this work, we evaluate the electrochemical properties of two interlayer materials, Si and LiXAl(2-x/3)O3 (LiAlO), at the Li7P3S11 (LPS)/Li interface. Compared to the Li/LPS/Li symmetric cells in absence of interlayers, the presence of Si and LiAlO both significantly enhance the cycle number and total charge passing through the interface before failures resulting from cell shorting. In both cases, the noted improvements were accompanied by cell impedances that had increased substantially. The data reveal that both interlayers prevent the direct exposure of LPS to the metallic Li, and therefore eliminate the intrinsic LPS decomposition that occurs at Li surfaces before electrochemical cycling. After cycling, a reduction of LPS to Li2S at the interface when a Si interlayer is present; LiAlO, which functions to drop the potential between Li and LPS, suppresses LPS decomposition processes. The relative propensities towards SE decomposition follows from the electrochemical potentials at the interface which are dictated by the identities of the interlayer materials. This work provides new insights into the phase dynamics associated with specific choices for SE/electrode interlayer materials and the requirements they impose for realizing high efficiency, long lasting all-solid batteries.

Biography:

Bergens research develops new catalysts for electrochemical energy conversion, for preparation of chiral pharmaceuticals, and recently, for storage of sunlight in fuels. Energy research highlights include one of the first in-situ observations of dynamic water distributions in fuel cells made with Magnetic Resonance Imaging. He developed catalysts for methanol fuel cells with controlled surface compositions. He also developed bench top, open air, one reaction preparations of highly active, stable catalysts for water oxidation in acid and base. He recently discovered new, active photoelectrodes for solar-powered water oxidation, and active electrocatalysts for CO2 reduction that are being coupled with chromophores.

Abstract:

Dye-sensitized photoelectrochemical cells often utilize molecular dyes and catalysts bonded to semiconductors to absorb sunlight, split water, and reduce carbon dioxide in order to store solar engery in hydrocarbon form.1 We have developed molecular bricks that bond by covalent or electrostatic interactions. We will report on the use of these bricks to construct several systems to study visible light photoelectrochemical oxidations and reductions under acidic, neutral, and basic conditions. For example, we grafted 1,10-phenanthroline by a covalent bond at C5 to a variety of semiconductors and glassy carbon electrodes using diazonium chemistry.2,3 We then used this electrode-ligand brick to build a number of grafted [Ru(phensurface)(aromatic diamine)2]2+ chromophores by displacement of MeCN from the corresponding [Ru(MeCN)2(aromatic diamine)2]2+ precursors. Further, incorporation of one 1,10-phenanthroline-5,6-dione ligand into the Ru(MeCN)2 precursor allows for subsequent modifications of the chromophore after it is grafted to the electrode surface. Specifically, condensation reactions between the dione group in the grafted chromophore, and diamines in solution allowed for systematic tuning of the efficiency and wavelength range of the photoelectrode. As well, electrostatic self-assembly between the cationic Ru-chromophore surfaces and anionic, hydrous oxide Ir-Ni nanoparticle catalysts prepared test photoanodes for water splitting. Similar building reactions were used to covalently attach Mn- and Re-based CO2 reduction electrocatalysts to electrode surfaces.