Surface Structural Changes of Perovskite Oxides during Oxygen Evolution in Alkaline Electrolyte

69 Pages·2013·7.87 MB·English

Surface Structural Changes of Perovskite Oxides during
Oxygen Evolution in Alkaline Electrolyte
MCHIVEs
ASSACHUSETV1S INS71TrE~
F TECHNOLoY
by
UN 2 5 2
Kevin J. May BRA S
B.Eng., Engineering Physics, McMaster University (2010)
SUBMITTED TO THE DEPARTMENT OF MECHANICAL ENGINEERING
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE IN MECHANICAL ENGINEERING
at the
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
June 2013
@ 2013 Massachusetts Institute of Technology
All rights reserved.
Signature of Author.......... ............. ... .. .......................
Department of Mechanical Engineering
May 10, 2013
C ertified by........................................... .....
7. . .Yang Shao-Horn
Gail . Kendall Professor of Mechanical Engineering
Thesis Supervisor
Accepted by......... ................... ....... ........................
David E. Hardt
Ralph E. and Eloise F. Cross Professor of Mechanical Engineering
Chairman, Department Graduate Committee
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Surface Structural Changes of Perovskite Oxides during
Oxygen Evolution in Alkaline Electrolyte
by
Kevin J. May
Submitted to the Department of Mechanical Engineering
on May 10, 2013 in Partial Fulfillment of the
Requirements for the Degree of Master of Science in
Mechanical Engineering
Abstract
Perovskite oxides such Bao.5Sr0 Co 08FeO 803 6 (BSCF82) are among the most active
catalysts for the oxygen evolution reaction (OER) in alkaline solution reported to date.
In this work it is shown via high resolution transmission electron microscopy (HRTEM)
and Raman spectroscopy that oxides such as BSCF82 rapidly undergoes amorphization
at its surface under OER conditions, which occurs simultaneously with an increase in
the pseudocapacitive current and OER activity. This amorphization was not detected at
potentials below those where significant OER current was observed. Lower
concentrations of Sr'- and Ba' are found in the amorphous regions of BSCF82.
Perovskite oxides with lower OER activities such as LaCoO (LCO) and LaMnO
3 3
(LMO) remained crystalline under identical electrochemical conditions. In addition, the
OER activity and tendency for amorphization are found to correlate with the oxygen p-
band center as calculated using density functional theory. This work illustrates that the
surface structure and stoichiometry of oxide catalysts can differ significantly from the
bulk during catalysis, and that understanding these phenomena is critical for designing
highly active and stable catalysts for the OER.
Thesis Supervisor: Yang Shao-Horn
Title: Gail E. Kendall Professor of Mechanical Engineering
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List of Publications
1. Grimaud, A., Carlton, C.E., Risch, M., Hong, W.T., May, K.J. & Shao-Horn, Y.
On the Influence of Cobalt and Manganese Coordination on the Catalytic Activity of
Perovskites for Oxygen Evolution. Submitted.
2. Grimaud, A., May, K.J., Carlton, C.E., Lee, Y.-L., Risch, M., Zhou, J. & Shao-
Horn, Y. Double Perovskites as a New Family of Highly Active Catalysts For
Oxygen Evolution in Alkaline Solution. Submitted.
3. Ming, T., Suntivich, J., May, K.J., Stoerzinger, K.A. & Shao-Horn, Y. Visible
Light Photo-Oxidation in Au Nanoparticle Sensitized SrTiO,:Nb Photoanode.
Submitted.
4. Risch, M., Grimaud, A., May, K.J., Stoerzinger, K.A., Chen, T.J., Mansour, A.N.,
& Shao-Horn, Y. Structural Changes of Cobalt-based Perovskites upon Water
Oxidation Investigated by EXAFS. The Journal of Physical Chemistry C 117, 8628-
8635 (2013).
5. May, K. J., Carlton, C.E., Stoerzinger, K.A., Risch, M., Suntivich, J., Lee, Y.-L.,
Grimaud, A., & Shao-Horn, Y. The Influence of Oxygen Evolution during Water
Oxidation on the Surface of Perovskite Oxide Catalysts. The Journal of Physical
Chemistry Letters 3, 3264-3270 (2012).
6. Lee, Y., Suntivich, J., May, K. J., Perry, E. E. & Shao-Horn, Y. Synthesis and
Activities of Rutile Ir0 and RuO Nanoparticles for Oxygen Evolution in Acid and
2 2
Alkaline Solutions. The Journal of Physical Chemistry Letters 3, 399-404 (2012).
7. Suntivich, J., May, K. J., Gasteiger, H. A., Goodenough, J. B. & Shao-Horn, Y. A
Perovskite Oxide Optimized for Oxygen Evolution Catalysis from Molecular Orbital
Principles. Science 334, 1383-1385 (2011).
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Acknowledgements
I would first like to acknowledge my advisor, Professor Yang Shao-Horn, for not
only her academic and research-oriented guidance but also for giving unwavering
support in all other aspects of my graduate career. You have believed in my abilities as
a student and researcher, and fostered my independence and creativity; I have learned
so much more than just science and research during my time at MIT because of this.
Thank you.
Funding for this work is gratefully acknowledged. Support was received from the
MRSEC Program of the National Science Foundation (DMR-0819762), Eni S.p.A. under
the Eni-MIT Alliance Solar Frontiers, and the DOE Hydrogen Initiative Program (DE-
FG02-05ER15728). I also received support from the Natural Sciences and Engineering
Research Council of Canada (PGS-M).
I would like to also extend my appreciation and thanks to my fellow lab members
in the Electrochemical Energy Lab for their friendship and support. Both present and
past, the students and postdoctoral researchers in this group are the best I could ever
imagine working with. I appreciate the support of everyone in the group, and would like
to mention some members in particular who have contributed to the scientific work in
this thesis: Jin Suntivich, for his enthusiasm in teaching the fundamentals of
electrochemistry and for providing mentorship when I was beginning my graduate
studies, which significantly shaped my way of scientific thinking and how I approach
research; Chris Carlton, for his TEM expertise and helpful discussions in the broader
subject of materials science; Kelsey Stoerzinger for her Raman spectroscopy
contributions; Marcel Risch for assisting in electrode preparation for Raman
spectroscopy and for his expertise in amorphous cobalt oxides and electrochemistry;
Yueh-Lin Lee for density functional theory calculations, and Alexis Grimaud for always-
helpful discussions in solid state chemistry and synthesis of perovskite oxide compounds.
I also thank my family for their love and support, for making me the person I am
today and also for giving me all the opportunities I needed to succeed. My parents never
faltered in fostering my curiosity and encouraging me unconditionally in my endeavors.
To Megan and Brandon, I'm lucky to have you as siblings, and I know I can always rely
on you for support.
Finally, I want to give my love and gratitude to Sana, for being my other half
through thick and thin. You have given me the strength and confidence to persevere
through any challenges that arise. This has helped me so much, perhaps even more than
you know. Thank you for being who you are and for being my partner in everything.
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Table of Contents
A b st r a ct ........................................................................................................................ 3
List of Publications ..................................................................................................... 5
A cknow ledgem ents................................................................................................. 7
List of Figures ............................................................................................................. 11
List of Tables .............................................................................................................. 15
1 Introduction ........................................................................................................... 17
1 .1 M o tiv a tio n ........................................................................................................ 17
1.2 The Oxygen Evolution Reaction: Historical Overview ...................................... 18
1.3 Perovskite Oxides as Oxygen Evolution Catalysts........................................ 23
1.4 Scope of this Thesis....................................................................................... 26
2 Experim ental..........................................................................................................29
2.1 Oxide Synthesis and Characterization........................................................... 29
2.2 Electrode Preparation .................................................................................. 31
2.3 Electrochem ical M easurements.......................................................................31
2.4 Characterization of Electrochem ically-Cycled Electrodes.............................. 32
2.5 Density Functional Theory Calculations ...................................................... 34
3 R esults and D iscussion..................................................................................... 35
3.1 M aterial Characterization ............................................................................ 35
3.2 Electrochem ical M easurem ents.......................................................................37
3.3 Transm ission Electron M icroscopy ................................................................. 42
3.4 Raman Spectroscopy and Potential-Dependent Amorphization .................... 48
3.5 Am orphization and Pseudocapacitive Current .............................................. 51
3.6 0 p-band Center: A Descriptor from Density Functional Theory .......... 54
4 Conclusions and Looking Forward ................................................................ 57
5 R e fe re n c e s .............................................................................................................. 6 1
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