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Previous EEL Research Highlights

Water Reactivity on the LaCoO₃ (001) Surface: An Ambient Pressure X-ray Photoelectron Spectroscopy Study

Stoerzinger, K.A., W.T. Hong, E.J. Crumlin, H. Bluhm, M.D. Biegalski, and Y. Shao-Horn

Abstract:

The reactivity of water with the (001)pc surface of epitaxial LaCoO₃ (LCO) thin films was investigated as a function of relative humidity (RH) by ambient pressure X-ray photoelectron spectroscopy. Significant changes were found in the O 1s and C 1s core-level spectra at different RHs, which were deconvoluted to yield new insights into the hydroxylation and hydration of the LCO surface. Continue reading.

(Left) Sample holder (see Whaley et al. for further detail) used for the measurements. (Middle) Schematic of Ambient Pressure X-ray Photoelectron Spectroscopy (AP-XPS) at a synchrotron. (Right) Temperature-dependent coverage of oxygen surface species in the presence of water. Three distinct surface-water interaction regimes were observed with increasing relative humidity: an initial hydroxylation, followed by a saturation regime after which carbonates begin to displace hydroxyl groups, and then adsorption of water molecules. The high basicity of lanthanum and the polar nature of the (100) orientation of LaCoO₃ contributes to greater degrees of surface hydroxylation and (bi)carbonate formation at low relative humidity compared to binary transition metal oxides.

Revealing the Atomic Structure and Strontium Distribution in Nanometer-Thick La_0.8Sr_0.2CoO_3-δ Grown on (001)-Oriented SrTiO₃

Zhenxing Feng, Yizhak Yacoby, Wesley Hong, Hua Zhou, Michael Biegalski, Hans Christen and Yang Shao-Horn

Abstract:

Surface segregation in metal oxides can greatly influence the oxygen transport and surface oxygen exchange kinetics critical to the performance of solid-state devices such as oxygen permeation membranes and solid oxide fuel/electrolytic cell electrodes. Unfortunately detecting elemental distributions at the atomic scale near the surface remains challenging, which hampers the understanding of underpinning mechanisms and control of surface segregation for the design of high-performance materials. Using the coherent Bragg rod analysis (COBRA) method, we report the first direct 3D atomic imaging of a 4 nm-thick “La_0.8Sr_0.2CoO_3–δ”/SrTiO₃ epitaxial film. Continue reading.

APS Science Highlight: Peeling Back the Layers of Thin Film Structure and Chemistry

Researchers gained new insight into thin-film superiority by probing the structure of perovskites at the the U.S. Department of Energy's Advanced Photon Source (APS), Argonne National Laboratory. They used a groundbreaking approach to tease apart the thin-film structure and chemistry layer-by-layer. Continue reading.
Erika Gebel Berg, Argonne National Laboratory

The layer-by-layer analysis of the concentration of strontium within a 40-angstrom thick (La, Sr)CoO thin film applied to a SrTiO₃ substrate. Examples of 3-D electron density maps of layers within the thin film are shown (top) along with a crystal model inset.

Double Perovskite as a Family of Highly Active Catalysts For Oxygen Evolution in Alkaline Solution

Alexis Grimaud, Kevin J. May, Christopher E. Carlton, Yueh-Lin Lee, Marcel Risch, Wesley T. Hong, Jigang Zhou and Yang Shao-Horn

Abstract:

New catalysts for the oxygen evolution reaction in basic solution are important for energy storage applications. Here, the authors report the high activity and stability of double perovskites in this role, and their performance is interpreted with regard to the proximity of the oxygen p-band to the Fermi level.

Watch a short movie of the catalyst evolving oxygen.

MIT News Article: New materials improve oxygen catalysis

Highly active catalysts could be key to improved energy storage in fuel cells and advanced batteries.
David L. Chandler, MIT News Office

The MIT web page on 18 September 2013 showing the molecular structure of double perovskites which consist of barium (green) and a lanthanide (purple) being arranged within a crystalline structure of cobalt (orange) and oxygen (red). Illustration: Christine Daniloff/MIT

In Situ Transmission Electron Microscopy Observations of Electrochemical Oxidation of Li₂O₂

Li Zhong, Robert R. Mitchell, Yang Liu, Betar Gallant, Carl V. Thompson, Jian Yu Huang, Scott Mao and Yang Shao-Horn

Abstract:

In this Letter, we report the first in situ transmission electron microscopy observation of electrochemical oxidation of Li₂O₂, providing insights into the rate limiting processes that govern charge in Li–O₂ cells. In these studies, oxidation of electrochemically formed Li₂O₂ particles, supported on multiwall carbon nanotutubes (MWCNTs), was found to occur preferentially at the MWCNT/Li₂O₂ interface, suggesting that electron transport in Li₂O₂ ultimately limits the oxidation kinetics at high rates or overpotentials.

Watch our movies of Li₂O₂ oxidation: movie 1, movie 2 and movie 3.

MIT News Article: Team observes real-time charging of a lithium-air battery

Imaging reveals what happens during charging; could lead to improved batteries for electric cars.
David L. Chandler, MIT News Office

(Left) MIT graduate researchers Robert Mitchell and Betar Gallant connect a Li-air battery used to prepare the samples for in-situ Transmission Electron Microscope (TEM) characterization. Photo: Jin Suntivich
(Right) Oxidation of Li₂O₂ particles monitored by TEM.

In Situ Ambient Pressure X-ray Photoelectron Spectroscopy Studies of Lithium-Oxygen Redox Reactions

Yi-Chun Lu, Ethan J. Crumlin, Gabriel M. Veith, Jonathon R. Harding, Eva Mutoro, Loïc Baggetto, Nancy J. Dudney, Zhi Liu & Yang Shao-Horn

Abstract:
The lack of fundamental understanding of the oxygen reduction and oxygen evolution in nonaqueous electrolytes significantly hinders the development of rechargeable lithium-air batteries. Here we employ a solid-state Li_4+xTi₅O₁₂/LiPON/Li_xV₂O₅ cell and examine in situ the chemistry of Li-O₂ reaction products on Li_xV₂O₅ as a function of applied voltage under ultra high vacuum (UHV) and at 500 mtorr of oxygen pressure using ambient pressure X-ray photoelectron spectroscopy (APXPS). Under UHV, lithium intercalated into Li_xV₂O₅ while molecular oxygen was reduced to form lithium peroxide on Li_xV₂O₅ in the presence of oxygen upon discharge. Interestingly, the oxidation of Li₂O₂ began at much lower overpotentials (~240 mV) than the charge overpotentials of conventional Li-O₂ cells with aprotic electrolytes (~1000 mV). Our study provides the first evidence of reversible lithium peroxide formation and decomposition in situ on an oxide surface using a solid-state cell, and new insights into the reaction mechanism of Li-O₂ chemistry. more

MIT News Article: New technique reveals lithium in action

Fundamental reactions behind advanced battery technology, revealed in detail by advanced imaging method, could lead to improved materials.

David L. Chandler, MIT News Office

A solid-state lithium-air battery (highlighted in orange) is positioned inside a test chamber at the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory, in preparation for its testing using X-ray photoelectron microscopy. Image courtesy of Eva Mutoro and Ethan Crumlin, ALS

Current Research Highlight