edited by
Mathieu Marrony
ProtonConducting
Ceramics
From Fundamentals
to Applied Research
ProtonConducting
Ceramics
ProtonConducting
Ceramics
From Fundamentals
to Applied Research
editors
Preben Maegaard
Anna Krenz
Wolfgang Palz
edited by
Mathieu Marrony
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Proton-Conducting Ceramics:
From Fundamentals to Applied Research
Copyright © 2016 by Pan Stanford Publishing Pte. Ltd.
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ISBN 978-981-4613-84-2 (Hardcover)
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Printed in the USA
Contents
Foreword
Preface
1. Proton Hydration and Transport Properties in ProtonConducting Ceramics: Fundamentals and Highlights
P. Berger, F. Mauvy, J.-C. Grenier, N. Sata, A. Magrasó,
R. Haugsrud, and P. R. Slater
1.1
Thermodynamics of Hydration 1.1.1 Formation of Protonic Defects:
Generalities
1.1.2 Thermodynamic Parameters
1.1.3 Correlation of Thermodynamic and
Physicochemical Parameters 1.2
Proton Transport Mechanisms 1.2.1 Principles
1.2.2 Grain Boundary Resistance and
Space Charge Layer Effects 1.2.2.1 The brick-layer model
1.2.2.2 Space charge layer: The theory
1.2.2.3 Space charge layer model
applied to proton conductors
1.3
Characterization Tools
1.3.1 Electrochemical Impedance
Spectroscopy
1.3.1.1 Principles
3.2.3.2 Examples
3.2.3.3 Analysis
1.3.2 Nuclear Microprobe
1.3.2.1 Principles and apparatus
1.3.2.2 Formal hydrogen diffusion
measurements 1.3.2.3 Hydrogen transport within
ceramic microstructure
1.3.3 Neutron Scattering
1.3.3.1 Interaction between proton
and neutron
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6
9
9
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27
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Contents
1.3.4
1.3.5
1.3.6
1.3.7
1.3.3.2 Neutron diffraction
1.3.3.3 Inelastic neutron scattering
1.3.3.4 Quasi-elastic neutron
scattering
Thermogravimetric Analysis
1.3.4.1 Thermogravimetric analysis
of proton-conducting
ceramics as electrolyte
1.3.4.2 Thermogravimetric analysis
of electrode materials
Infrared Spectroscopy
1.3.5.1 Infrared absorption
1.3.5.2 Transmission spectroscopy 1.3.5.3 Reflection spectroscopy Raman Investigation of Proton
Insertion in Oxide Ceramics
Electronic and Local Structure with
X-Ray Spectroscopic Techniques
1.3.7.1 Background methodology
1.3.7.2 Examples of uses
2. Proton-Conducting Oxide Materials
G. Taillades, J. Rozière, J. Dailly, N. Fukatsu,
A. Magrasó, R. Haugsrud, and P. R. Slater
2.1
Perovskites and Derivatives
2.1.1 Structural Characteristics and
Stability of ABO3-Based Simple
Perovskite
2.1.1.1 Structural properties
2.1.1.2 Formation of proton defects
and proton mobility through
ABO3-based perovskite
2.1.1.3 Proton conductivity and
stability of materials:
BaZrO3 against BaCeO3
2.1.2 Mixed Ce, Zr-Based, and Complex
Perovskite Materials
2.1.3 Brownmillerite A2B2O5-Based
Materials
2.1.3.1 Structural properties
32
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37
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47
51
55
55
58
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74
77
82
88
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Contents
2.2
2.3
2.4
2.5
2.1.3.2 Hydration properties
2.1.3.3 Conductivity properties
2.1.3.4 Stability against CO2
Ortho-Phosphates, Ortho-Niobates, and
Ortho-Tantalates LnBO4
Rare-Earth Tungstates: Proton Conductors
with Fluorite-Related Structures
2.3.1 Stoichiometry and Crystal Structure 2.3.2 Conducting Properties and Doping
Strategies
2.3.3 Chemical Stability and Mechanical
Properties of Lanthanum Tungstate
(Other) Fluorite- and Pyrochlore-Related
High-Temperature Proton Conductors Other Components
2.5.1 Acceptor-Doped Corundum (Alumina)
2.5.1.1 Proton conduction in
acceptor-doped alumina:
a short history
2.5.1.2 Location of movable
proton in crystal lattice
2.5.1.3 Drift mobility of proton
2.5.1.4 Electrochemical properties
2.5.2 Composite Oxides/Oxyacid Salts: The
“Intermediate” Proton Conductors
2.5.3 Mixed Protonic Electronic Conductors
2.5.3.1 Introduction
2.5.3.2 Trivalent doped perovskites
2.5.3.3 New class of proton
conductors
2.5.3.4 Multivalent component–
doped proton conductors
2.5.3.5 Ni–X cermet materials
3. Synthesis and Processing Methods: Low Cost
and Easy Industrial?
G. Taillades, P. Briois, J. Dailly, M. Marrony, and N. Sata
3.1
Synthesis Methods
3.1.1 Solid Route
3.1.1.1 Solid-state reaction
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Contents
3.2
3.1.1.2 Solid-state reactive sintering
3.1.1.3 Mechanosynthesis of
nanopowders of protonconducting electrolyte
materials
3.1.2 Sol–Gel Methods
3.1.2.1 The Pechini method
3.1.2.2 Hydrogelation of acrylates
3.1.3 Coprecipitation
3.1.3.1 Oxalate precipitation route
3.1.3.2 Carbonates and hydroxide as
precipitants
3.1.4 Combustion Synthesis
3.1.4.1 Glycine or urea solution
combustion
3.1.4.2 Citrate–nitrate
autocombustion
3.1.5 Other Wet-Chemical Routes
3.1.5.1 Reverse micelle method
3.1.5.2 Spray pyrolysis
Processing Routes
3.2.1 Pressing/Copressing Methods
3.2.1.1 Principle
3.2.1.2 Compaction defects
3.2.1.3 Isostatic compaction
3.2.1.4 Mechanics of pressing
3.2.1.5 Sintering step
3.2.2 Plasma Techniques
3.2.2.1 Magnetron sputtering
3.2.2.2 Thermal spraying
3.2.3 Humid Routes
3.2.3.1 Tape-casting method
3.2.3.2 Screen-printing method
3.2.3.3 Case of coating methods
on an anode tubular support
3.2.4 Other Routes
3.2.4.1 Single crystal
3.2.4.2 Pulsed laser deposition
3.2.4.3 Epitaxial growth
3.2.4.4 Super lattice and multilayers
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270
Contents
4. Typical Applications of Protonic Ceramic Cells:
A Way to Market?
M. Marrony, H. Matsumoto, N. Fukatsu, and M. Stoukides
4.1
Proton-Conducting Material: An
Electromotive Force 4.1.1 Components in Fuel Cell Devices 4.1.1.1 Electrochemical
performance 4.1.1.2 Influence of parameter keys
on protonic ceramic cell
performance: fuel quality
and operating conditions
4.1.1.3 Reliability assessment
4.1.1.4 Toward the protonic
ceramic cell scaling-up
4.1.2 Membrane Signals (Hydrogen
Sensors) 4.1.2.1 Open-circuit voltage of
galvanic cell based on
proton-conducting ceramics
4.1.2.2 Design of hydrogen sensor
considering the use and the
properties of materials
4.1.2.3 Performance and reliability
of hydrogen sensor for
practical use
4.2
Proton-Conducting Material:
An Electrochemical Hydrogen Transport
4.2.1 Membrane Separators 4.2.1.1 Type of materials and
mechanisms for hydrogen
separation
4.2.1.2 Hydrogen pumps
4.2.1.3 Electrode materials and
activity correlating with
electrolyte
4.2.1.4 Mixed conducting membrane
4.2.2 Electrolyte in Steam Electrolysis
4.2.2.1 Basic principle
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337
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343
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352
ix
x
Contents
4.3
4.4
4.2.2.2 Performance and reliability
of proton-conducting
ceramic cell in steam
electrolysis
Proton-Conducting Material as Membrane
Reactors
4.3.1 Introduction, Operation Modes,
and Designs of a PCCR
4.3.2 Applications of PCCR: Methods and
Techniques Used
4.3.2.1 Selective conduction of ions
4.3.2.2 Electrochemical promotion
of catalytic reactions
4.3.2.3 Chemical cogeneration
4.3.2.4 Methane conversion to C2
hydrocarbons
4.3.2.5 Other reactions of methane
activation 4.3.2.6 Decomposition of alcohols 4.3.2.7 Reactions of alkanes and
alkenes 4.3.2.8 Forward and reverse water
gas shift 4.3.2.9 Decomposition and
reduction of NOx 4.3.2.10 Reactions of sulfur
compounds Proton-Conducting Material as
Electrocatalyst in Solid-State Ammonia
Synthesis 4.4.1 Introduction: Catalytic vs.
Electrocatalytic NH3 Synthesis 4.4.2 Solid-State Ammonia Synthesis in
Proton-Conducting Cell Reactor:
Methods and Materials Tested 4.4.3 Electrochemical Promotion during
SSAS
General Conclusion
Index
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361
364
364
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373
374
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374
375
377
377
378
383
405
413
Contents
Foreword
Three Decades of Ceramic
Proton Conductors: The Road to
Commercialization
Two pivotal events took place in 1981 forever shaping the future
of the field of protonic conduction in solids. In that year, the first
conference on Solid State Protonic Conductors was organized by
Philippe Colomban, and convened in Paris as a joint Danish–French
working group. By this time there was sufficient interest in solid
proton conductors to warrant such a meeting. In that same year,
Hiroyasu Iwahara and colleagues1 published a paper in the journal
Solid State Ionics entitled “Proton Conduction in Sintered Oxides and
its Application to Steam Electrolysis for Hydrogen Production”. The
significance of the discovery of high-temperature ceramic proton
conductors by Iwahara cannot be overstated, but the paper went
largely unnoticed for years. The Danish–French workshop, now
referred to as SSPC-I,2 was focused broadly on proton conduction
in solids, and the connection to proton transport in perovskite
ceramics at elevated temperature was not fully appreciated at that
time. The proceedings of SSPC-I, II, and III were published by the
Odense University Press, and beginning with SSPC-4 (1988), the
proceedings were published in the journal Solid State Ionics.3 This
meeting in Exeter, Great Britain, was the first SSPC Conference
attended by Dr. Iwahara. Even as late as 1989, Robert Slade,
1Iwahara, H., Eska, T., Uchida, H., and Maeda, N. (1981). Proton conduction in sintered
oxides and its application to steam electrolysis for hydrogen production, Solid State
Ionics, 3/4, pp. 359–433.
2Thomas J.O., SSPC-12 Chairman (2005). Preface to the Special Proceedings of the
12th International Conference on Solid State Proton Conductors, Solid State Ionics,
176, p. 2837.
3Slade R.T., SSPC-4 Chairman (1989), Preface to the Special Proceedings of the 4th
International Conference on Solid State Proton Conductors, Solid State Ionics 35, pp.
1–2.
xi
xii
Foreword
chairman of SSPC-4, mentioned “the relatively new field” of protonic
electrolytes and commented in the proceedings preface, “The
development of create protonic conductors for high temperatures
was both a major step forward and also contrary to the accepted
wisdom that ceramic processing precludes protonic conductivity”.
This statement expresses the skepticism that existed for nearly 10
years after Iwahara’s discovery.
The story of Iwahara’s discovery of ceramic proton conductors
actually dates back considerably further. The first suggestion
of proton conduction in lanthanum aluminate ceramics was by
the Frenchman Francis Forrat and coworkers in 1964.4 Shortly
thereafter, the possibility of high-temperature hydration by filling
oxygen ion vacancies in ceramic oxides with hydroxyl ions was
formally proposed by Stotz and Wagner in 1966.5 Forrat mistakenly
attributed proton transport to cation vacancies in what was thought
to be AlLa(1–x)HxO3. Iwahara later showed, however, that the correct
formulation for doped lanthanum aluminate is La(1–x)MxAlO3-d,
and that the conductivity observed by Forrat was probably due to
oxygen ions on the anion sublattice. Nonetheless, the possibility of
proton conduction in ceramics at elevated temperatures was out in
the open. Armed with practical experimental techniques in hightemperature solid-state electrochemistry, Iwahara and Takahashi
carried out the first systematic investigation of ionic conduction in
perovskite ceramics, published in 1971.6 Throughout the seventies,
they improved their experimental techniques and recognized the
unusual emf behavior in certain perovskites that could only be
explained by proton transport. Iwahara and Takahashi published
their original paper on proton conductivity of lanthanum–yttrium
oxide and strontium zirconate in 1980 in a rather obscure French
journal,7 which had almost no impact on the field for many years.
4Forrat F., Dauge G., Trevoux P., Danner G., and Christen M. (1964). Electrolyte solide
à base de AlLaO3. Application aux piles à combustible, Comptes Rendus de l’Académie
des Sciences, 259, p. 2813–2816.
5Stotz V.S. and Wagner C. (1966). Die Löslichkeit von Wasserdampf und Wasserstoff
in festen Oxiden, Berichte der Bunsengesellschaft für physikalische Chemie, 70, pp.
781–788.
6Takahashi T. and Iwahara H. (1971). Ionic conduction in perovskite-type oxide solid
solutions and its application to the solid electrolte fuel cell, Energy Conversion, 11,
pp. 105–111.
7Takahashi T. and Iwahara H. (1980). Solid state ionics: Proton conduction in
perovskite type oxide solid solutions, Revue de Chimie Minerale, 17, p. 243.
Foreword
In the introduction it is claimed that, “The present authors have
found that the solid solutions based on lanthanum–yttrium trioxide
(LaYO3) and strontium–zirconium trioxide (SrZrO3) could show a
proton conduction in hydrogen gas. The proton conduction in these
solid solutions has been confirmed by an electrochemical method.”
It is this paper that properly marks the invention of ceramic proton
conductors, and it is surprising today that this historic discovery
went virtually unknown for years. John Goodenough did not
mention Iwahara’s work in his review of the status of ceramic proton
conductors presented at SSPC-II in 1982.8
Notwithstanding the slow start, Iwahara envisioned hydrogen–
air fuel cells, steam electrolysis cells, hydrogen separation
membranes and hydrogen sensors from the very beginning. The
steam concentration cell was proposed as a way to “recover energy
from exhaust gas . . . in industrial plants” in 1982.9 An important
new branch of protonic ceramic applications in membranes for
hydrogenation and dehydrogenation of hydrocarbon gases was
first demonstrated by Iwahara in 1988.10 This paved the way for
the important commercial applications as membrane reactors
demonstrated by Hamakawa’s group11 and the advent of methane
dehydroaromatization as a method for converting natural gas to
liquids by a non-oxidative route. In a review paper in 1992,12 Iwahara
identified 12 diverse applications for ceramic proton conductors,
which he had demonstrated in his lab that provided compelling
evidence for the utility of the technology. These were broadly
classified as (1) sensors, (2) fuel cells, (3) hydrogen separation,
(4) electrolyzers, and (5) membrane reactors. In a presentation
in Schwäbisch, Germany, at SSPC-7 in 1995, Iwahara described 15
8Goodenough J.B. (1982), Solid state ionic conductors, Proceedings of SSPC-II,
Hindsgavl Castle, Denmark, Odense University Press, pp. 123–142.
9Uchida H., Maeda N. and Iwahara H. (1982). Steam concentration cell using a
high-temperature type proton conductive solid electrolyte, Journal of Applied
Electrochemistry, 12, pp. 645–651.
10Iwahara H. (1988). High-temperature proton-conducting oxides and their
applications to solid electrolyte fuel cells and steam electrolyzer for hydrogen
production, Solid State Ionics, 28–30, pp. 573–578.
11Hamakawa S., Hibino T., and Iwahara, H. (1993). Electrochemical methane coupling
using protonic ceramics, Journal of the American Ceramic Society, 140(2), pp. 459–
462.
12Iwahara H. (1992). High-temperature protonic conductors and their applications,
Solid State Ionics, 178(7–10), pp. 575–586.
xiii
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Foreword
commercial applications for ceramic proton conductors, which
he claimed were “positively verified to work”. This paper entitled
“Technological Challenges in the Application of Proton-Conducting
Ceramics”,13 provides a virtual road map for commercialization
of the technology. The only significant application for ceramic
proton conductors that Iwahara did not mention—solid state
ammonia synthesis and the corresponding ammonia fuel cell—
were demonstrated for the first time by Marnellos and Stoukides
in 1998.14 These electrochemical applications and a host of nongalvanic devices using mixed ionic/electronic protonic conductors,
cermets, and cercers were widely considered to be commercially
viable by 2000. How is it possible, then, that as of 2014 there is still
no successful commercial product except a small sensor initiative?
By contrast, the transistor was discovered in 1947, and already
by 1956 Sony had transistor radios on the market. The technical
feasibility of ceramic proton conductors for many applications had
been demonstrated by 2000, but unlike early germanium transistors,
commercial viability was lacking. The problem was one of finding
suitable materials. By happy coincidence, germanium crystals of
sufficient purity were already available in 1947, so that transistors
could be fabricated that worked well enough for early commercial
applications. This gave impetus to semiconductor development
through relatively short product development cycles that led to silicon
and the proliferation of devices enabled by it. No such development
was possible for ceramic proton conductors, because there was no
material that worked well enough for commercialization. The first
successful commercial application for ceramic proton conductors
was for a hydrogen sensor based on In-doped calcium zirconate
at TYK Corp., and is sold today under the tradename “Notorp”. The
first commercialization initiative for protonic ceramic fuel cells
was Protonetics International, Inc., in 2000. The leading candidate
material at the time was yttrium-doped barium cerate, BCY, but
when it became apparent that BCY was chemically unstable in carbon
dioxide and steam under the operating conditions, the company was
13Iwahara H. (1995), Technological challenges in the application of proton-conducting
ceramics, Solid State Ionics, 77, pp. 289–298.
14Marnellos G. and Stoukides M. (1998), Ammonia synthesis at atmospheric pressure,
Science, 282, pp. 95–98.
Foreword
folded shortly thereafter, and it was “back to the drawing board” to
find a more suitable material.
Once it became widely recognized that pure perovskite cerates
would probably never be useful for widespread commercial
application, attention was focused on developing more stable ceramic
proton conductors. Yttrium-doped barium zirconate (BZY) was a
leading contender, championed most notably by Klaus Dieter Kreuer
during the 1990s,15 but the material proved almost impossible to
sinter using solid state reaction to prepare the precursor powders
followed by tradition ceramic sintering. This necessitated the use
of more exotic sintering methods not well suited for commercial
production. Furthermore, the ceramic materials tended to have small
grains with high grain boundary resistance to proton transport. The
critical breakthrough came in 2004 by the discovery of solid state
reactive sintering by Babilo and Haile.16 They demonstrated that
dense, large-grained BZY could be fabricated in a single processing
step from precursor powders, BaCO3, ZrO2, and Y2O3, with the
addition of a small amount of sintering additive such as ZnO. The
process is generally now called solid-state reactive sintering. The
impact of this discovery on commercial development of ceramic
proton conductors cannot be overstated. It may be compared to the
discovery of zone refining in semiconductor technology, which made
it possible to grow silicon crystals with sufficient intrinsic purity to
allow p- and n-type doping for manufacturing practical transistors.
With solid state reactive sintering (SSRS), it became possible to
fabricate practical ceramic proton conductors over the full range
of BCY to BZY. BaCexZr(0.9–x)Y0.1O3–d, BCZY, is an acceptor-doped
cubic ABO3 perovskite proton-conducting ceramic constituting a
complete solid solution between the end members, barium cerate,
and barium zirconate, for 0 ≤ x ≤ 0.9. The series has been recognized
for many years as, perhaps, the ideal ceramic proton conductor, but
compositions containing more than a few mol% Zr proved almost
impossible to sinter into a dense polycrystalline ceramic until the
discovery of solid-state reactive sintering. With SSRS, making dense
15Kreuer, K.D. (1999). Aspects of the formation and mobility of protonic charge carriers
and the stability of perovskite-type oxides, Solid State Ionics, 125, pp. 285–302.
P. and Haile, S.M. (2005). Enhanced sintering of yttrium-doped barium
zirconate by addition of ZnO, Journal of the American Ceramic Society, 88(9), pp.
2362–2368.
16Babilo,
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Foreword
and gas-tight BCZY membranes at a commercial scale became
possible for the first time.
The question of how long it should take between demonstrating
technical feasibility and commercial viability is an important
question for research scientists and engineers, because ultimately
commercial viability determines the availability of the required
investment capital. Is 30 years too long? The silicon semiconductor
story is perhaps misleading and has given unrealistic expectations
about how long commercialization of new technology should actually
take. The more appropriate analogy in semiconductor development
may be found in the III–V semiconductors. It was known almost
from the invention of the transistor that direct bandgap compound
semiconductors like GaAs offered superior properties, such as faster
operation, but making crystals of the materials with sufficient purity
turned out to be a daunting challenge. The first commercial application
did not become widely available until Sony and Phillips brought the
semiconductor laser to market in the form of the compact disc player
in 1978—31 years after the invention of the transistor. Even more
compelling is the story of wide bandgap light-emitting diodes. The
first red LEDs based on GaAs were produced by Monsanto in 1961,
but another 30 years were required before the first blue LEDs based
on GaN were produced—not because scientists did not know what to
look for—but because many materials science challenges had to be
overcome. Another 20 years were required before blue LEDs would
find their way into commercial applications for high-efficiency light
sources by companies like Phillips and Cree. It is easy to think that
commercialization should come quickly for innovations as disruptive
as ceramic proton conductors, but the pacing element with these,
as with semiconductors devices, generally rests with materials
scientists. The pace of commercialization cannot advance any faster
than the understanding of how to prepare the necessary materials
with the pre-requisite properties for the intended applications.
The chapters in this new book constitute the most comprehensive
and most up-to-date compilation of the science and technology of
ceramic proton conductors. The following chapters attest to the
enormous progress that has been made over the past three decades
by many of the leading scientists working in the field today. Although
there is still much to be learned, devices are now being fabricated
Foreword
using ceramic proton conductors that exhibit the necessary
properties for various commercial applications envisioned by Dr.
Iwahara 30 years ago, and I am confident that this technology is now
poised to revolutionize the field of energy sustainability in much
the same way that the transistor has revolutionized the information
age.
W. Grover Coors
Doctor in Materials Science
Research Professor in Metallurgical & Materials Engineering
Department at Colorado School of Mines
Chief Scientist at CoorsTek, Inc.
Golden, Colorado, USA
xvii
Preface
Preface
The worldwide energy demand and the associated increasing
environmental concerns has driven research more and more to find
alternatives for clean energy source. In such context, the hydrogen
economy has continuously grown since 1970s—date of the first
worldwide oil crisis.
Now, the trend is ready to promote the use of hydrogen as an
energy carrier in many strategic fields (transportation, distributed
energy conversion, gas separation . . . ). In particular, the research
of high- performing and reliable ionic-conducting materials likely
to valorize hydrogen source is fundamental. In such matter, two
kinds of ionic conducting material–based technologies coexist in the
research and development:
• The polymer-based technology used at low-temperature
domain below 300°C.
• The ceramic-based technology used at high-temperature
domain above 400°C.
Among the possible cation and anion conduction studied, the
proton is found in many different solid materials, from organic
polymers at room temperature to inorganic oxides (such as ceramics
and solid acids) at higher temperatures beyond 300°C. For more
than 40 years, it has played a very important role in many processes
implying diverse phenomena in biology, chemistry, or physics.
Especially, several studies have been carried out in the field of
proton-conducting membranes as electrolyte in the hydrogen chain
related to energy conversion and storage applications.
Thus, while proton-exchange polymer-based membranes
(commonly named PEM) are commercially used in the lowtemperature domain, proton-conducting ceramic-based materials
(labeled PCC) remain at an early stage of development at higher
temperatures. Notably, PCC technology has come up against the
merging of commercial oxygen ions O2-conducting solid oxide cell
(noted SOC) beyond 700°C.
xx
Preface
However, such high operation temperature implies the use of
costly ceramic materials into complex fabrication and the need for an
important energy input to achieve relevant cell performance. Besides,
it imposes to ceramic-based technology high thermal stresses caused
by thermal expansion mismatch of materials and therefore limited
operation profiles (low start-up kinetics, low thermal cycling).
As we can guess, the performance of such energy systems highly
depends on the properties of their core components, thus requiring
the synthesis and the development of high performing and reliable
ones, in particular, the ionic conducting electrolyte membrane which
constitutes the heart of the electrochemical device.
Thereby, intensive researches are yet being deployed for
appointing advanced generation of ceramic-based materials able
to operate at intermediate temperature between 400 and 700°C
while keeping reasonable performance and reliability. This lower
temperature of operation will allow easier cell construction, enabling
cheaper materials to be used, and will reduce the problem of thermal
stress.
In such quest, the theoretical intrinsic specificities of the proton
element (smallest size, high diffusion kinetics, etc.) brings better
electrical pathway in electrochemical devices versus the oxygen
ions. In particular, below 700°C, the proton-charge carriers become
advantageous for coupling higher kinetic and lower activation energy
needed in a ceramic matrix.
The last two decades revealed the merging of new families of
ceramic oxides on the basis of proton transport, which have the
main advantage of running at intermediate temperatures with better
electrical and mechanical properties than common SOC. They are
considered as promising electrolyte candidates for high-efficiency
electrochemical devices related to energy applications such as fuel
cell, water electrolysis system, hydrogen and humidity sensors,
catalytic membrane reactors, etc.
Many reviews and scientific articles have covered all main
aspects of PCC research starting from proton transport mechanism
principles to their synthesis and cell manufacturing techniques.
However, the refractory nature, the extreme process conditions, the
chemical stability toward carbon dioxide and water or the complex
transport phenomena mechanisms of the currently prevailing
Preface
proton-conducting ceramics remain as some important challenges
to propose their implementation in such devices.
And now, after 20 years of research and development, where are
we? What is the real value of PCC technology? Is it competitive with
conventional solid oxide technology? Can we consider any strategic
R&D pathways to deal with a profitable PCC market?
This book tends to humbly reply to such questions by joining in
the same approach some educational aspects of PCC technology for
the novices and some critical point of views of scientist experts in
the domain by promoting strategic routes for contributing to the
PCC merging market.
In this sense, the current book is based on four sections, dealing
with topics from raw materials to system applications.
Chapter 1 consists of three sections that deal with theories
and principles from the proton hydration process to the transport
properties through the ceramic matrix. It proposes notably some
main characterization tools likely to illustrate the proton presence.
Chapter 2 aims to give us an updated background of the most
promising families of proton-conducting ceramic oxides studied by
assessing their structural characteristics and their main intrinsic
chemical and electrical properties. For that, five types of material
oxides are considered:
•
•
•
•
•
the perovskite structure–based oxides
the acceptor-doped metal oxides
the fluorite structure–based oxides
the pyrochlore structure–based oxides
another more “exotic” type oxides
• the proton-conducting material as an electromotive force
Chapter 3 lists the main conventional and promising techniques
for the elaboration of compound materials of the cell with respect
to technical and structural specifications required for each layer of
cell. A special attention is brought to the industrialization level of
synthesis and manufacturing methods.
The last chapter, Chapter 4, of the book includes four sections,
each of which deals with the use of proton-conducting ceramics
in the most promising applications advised by the expertise of coauthors:
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Preface
• the proton-conducting material as an electrochemical
hydrogen transport
• the proton-conducting cell in solid-state ammonia synthesis
It should be noted that at the end of each section, a short summary
is proposed by including the main key points and recommendations
of co-authors.
Finally, I would like to acknowledge the support of all co-authors
who have expended huge “extra” time beyond their professional
time schedule to write and affine the description of this book. Its
success would also be their success . . .
Mathieu Marrony
Summer 2015