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Research Report

Ion Conductive Organic-inorganic Hybrid Electrolyte with Meso-scale
Proton Channels for Fuel Cells
Satoru Fujita, Kazuya Kamazawa, Satoru Yamamoto, Akihiko Koiwai, Shinji Inagaki, Jun Sugiyama
and Masaya Kawasumi
Report received on Nov. 13, 2014

Mesoporous electrolytes construct meso-scale proton-conducting channels by
self-assembly of ionic groups such as sulfonic acids in directional pathways. The behavior of proton
mobility significantly corresponds to the amount of acid groups and adsorbed water in the mesopores,
which play an important role as a proton source and proton carrier under hydrated conditions, respectively.
It is noteworthy that the proton diffusivity in the mesopores is enhanced by the higher densification of
sulfonic acid groups even at very small amounts of adsorbed water (H2O/SO3H = 2). Furthermore, under
dry conditions, the proton conductivity reaches 0.3 mS cm–1 with a surface acid density of up to 3.1 SO3H
molecules nm–2 at 160ºC. This value is higher than that for Nafion by about two orders of magnitude.
Such high proton conductivity is considered to be induced by proton hopping within the hydrogen-bonded
networks formed by neighboring sulfonic acid groups.
Organic-inorganic Hybrid, Self-assembly, Meso-scale Ion-conducting Channel,
Capillary Condensation of Water, Surface Acid Density, Hydrogen Bond Network,
Proton Conductivity

1. Introduction
Fuel cells (FCs) are an important energy conversion
technology and have emerged in the last decade asa keystone for future energy supplies.(1-3) FCs haveattracted much attention as clean energy sources
for numerous applications such as electric vehicles,
portable electronics and residential power generators,
because they exhibit a high power density andefficiency with low emission levels.(4,5)
However, there are a variety of issues such as cost,
durability, heat and water management, that need tobe resolved before FC systems can be commercialized
widely. To this end, many researchers have focused onelectrolytes with high conductivity, electrodes with low
Pt loading and membrane-electrode assembly (MEA)
designs that are suitable for practical FCs. One of themain challenges in current FC research is to develop an
electrolyte that can operate under higher temperatureand lower hydration conditions, as an alternative toperfluorosulfonic acid polymers such as Nafion.(6,7)
Generally, proton exchange membranes (PEMs) withhigh proton conductivity at temperatures between 100
and 200ºC are desirable, because operation at higher
temperatures can increase catalytic activity, simplify
heat and water management, and enhance the tolerance© Toyota Central R&D Labs., Inc. 2014of the Pt catalysts against CO poisoning.(8) The key tofast proton transport in electrolytes at high temperatureand low water content is thought to lie in constructing
the meso-scale morphology of sulfonic acid groups
as a proton source, designed so that protons can passefficiently. However, the continuity of meso-scale
proton pathways in perfluorosulfonic acid polymers
is almost lost above 100ºC and at low water content,
resulting in a concomitant decrease in conductivity.
Organic-inorganic hybrid mesoporous materials
also form meso-scale ion-conducting channels
by self-assembly of ionic groups such as sulfonicacids in directional pathways.(9-11) The most striking
characteristic of mesoporous materials with inorganic
pore walls is their mechanical and thermal durability.
This inorganic wall structure prohibits swellingwhen hydrated. Moreover, desirable water moleculesin the pores are retained by tailoring the sturdy
mesostructured channels. Thus, mesoporous materials
are expected to exhibit high proton conductivity athigher temperature and lower relative humidity (RH),
and allow significant optimization of electrochemical
performance.
In this review, we explain the relationship between
the proton diffusivity and the water sorption process
in uniform meso-scale proton channels of mesoporous
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silica materials. Furthermore, we demonstrate thehigh proton conductivities of mesoporous electrolytes
under dry or low RH conditions, and propose aproton conductivity mechanism for the materials
on the basis of the results of molecular dynamics(MD) simulations and quasielastic neutron scattering(QENS) measurements.
2. Experimental
2. 1 Preparation of Sulfonic Acid-functionalized
Mesoporous Electrolytes (Film and Powder)
Sulfonated mesoporous silica films (thickness ≈ 300 nm)
were coated on a substrate by the evaporation-induced
self-assembly (EISA) approach(12,13) from precursor
mixtures of tetramethoxysilane (TMOS) and3-mercaptopropyltrimethoxysilane (MPTMS) in thepresence of the surfactant alkyltrimethylammonium
chloride [CnH2n+1N(CH3)3Cl, n = 12, 14 and 18] (Fig. 1),
and treated with H2O2 to convert the functionalmoiety -SH in MPTMS into -SO3H. The films were
denoted as MPm-Cn (m is MPTMS content in mol%,and n is alkyl-chain length of surfactant). We also
prepared sulfonic acid-functionalized mesoporous
silica powders (MP10-C18 (p), MP30-C18 (p), andMP50-C18 (p)) with pore structures and sulfonic acidcontents comparable to those of the films (MP10-C18,
MP30-C18, and MP50-C18) in order to determine theproton diffusion by QENS measurements, because thiswas impossible with the thin films.

2. 2 Characterizations
2. 2. 1 Characterizations of Film
Transmission electron microscope (TEM) images
were recorded with a JEOL JEM-2000EX instrument
at an accelerated voltage of 200 kV. Krypton
adsorption-desorption isotherms at –186ºC wereobtained using a Quantachrome AUTOSORB-1. The
ion exchange capacity (IEC) in each electrolyte wasconfirmed by acid-base titrations. The surface aciddensity (SO3H molecules nm–2) in each electrolyte
was calculated from IEC and specific surface area
obtained by krypton adsorption. The water vapor
adsorption-desorption isotherms (water uptakes) of
the mesoporous electrolytes was measured using a
Quartz Crystal Microbalance (QCM) chip. In-plane
proton conductivity of the mesoporous electrolyte on asubstrate was measured by electrochemical impedance
spectroscopy using a Hioki 3532-50 LCR Hitester
instrument. The conductivity was calculated using thefollowing Eq. (1):σ = d / (SR) ,					

(1)where σ is the conductivity, d is the film thickness,
S is the area of cross section, and R is the resistancedetermined by the intersection of the semicircle inCole-Cole plots.
MD simulations were carried out to investigate theproton conductive mechanism for the model system

Evaporation Induced
Self-Assembly (EISA)
Removal of
surfactant
Surfactant

Pt electrodes

Fig. 1

substrate

Propyl-sulfonated mesoporous electrolyte
on Si substrate with Pt electrodes

Procedure of propyl-sulfonated mesoporous silica electrolyte obteined by Evaporation Induced Self-Assembly (EISA)
process.

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of mesoporous silica electrolyte corresponding to theexperimental materials. They were performed usinga Forcite module in Materials Studio (Accelrys, Inc.)
with a COMPASS forcefield and a Ewald summation
method.
2. 2. 2 Characterizations of Powder
A high-flux backscattering spectrometer (HFBS) at
NIST Center for Neutron Research (NCNR)(14) was
employed to measure proton diffusion in the powder
samples by QENS. A self-diffusion coefficient wascalculated by fitting a quasielastic broadening signal at
the elastic peak. The line broadening can be modeledin our system with a scattering function S(Q,ω) given
by Eq. (2):,						 (2)where Q is a momentum transfer, ω is a frequency, andu2 is an atomic displacement. In the above equation,
R(Q,ω) is an instrumental resolution function, δ(ω)
is a delta function representing an elastic peak, BG
is a background due to atomic vibrations, and L(Q,ω)
is a Lorentzian function that measures a quasielastic
broadening with the peak width Γ(Q) as given in
Eq. (3). We used a vanadium standard for instrumental
resolution.
			

(3)

3-2(h) and (i)). These results indicate that thesemesoporous electrolytes have well-defined andaligned 2D hexagonal mesostructures. On the contrary,
the structures of MP50-C18 film and MP50-C18 (p)powder showed a disordered phase with a worm-hole
structure (Figs. 3-1(g) and 3-2(j)). Table 1 lists IEC
for the mesoporous electrolytes. The IEC ranges
from 0.78 to 2.30 mmol g-1. These values are almost
comparable to the amounts of sulfonate groups in themesoporous films assuming 100% conversion of SH to
SO3H groups (theoretical IEC = 0.6 – 2.9 mmol g–1).
The IEC of MP50-C12 (2.3 mmol g-1) is significantly
higher compared to Nafion 112 membrane(0.9 mmol g-1).
3. 2 Proton Conductivity under Hydrated
Conditions
Figures 4(a) and (b) show the water uptake
λ = [H2O] / [-SO3H] (25ºC) for different RHs of thesulfonated mesoporous silica films. As a comparison,
Nafion 112 membrane and Nafion thin film for theadsorption process are also shown. Nafion thin film
(thickness: 200 nm) were coated on a substrate using
Nafion solution. According to increase in RH, theisotherms of the mesoporous films showed a gentle
increase at low RH, a steep increase at medium RH,
and almost a plateau at high RH. The gentle increaseat low RH is due to the adsorption of water on thepore surface and the clustering around the sulfonicacid groups. The steep increase and the plateau

3. Results and Discussion
3. 1 Characterization of Mesoporous Electrolytes
Figure 2 shows a TEM image of microtome-cut
MP40-C18 film embedded in epoxy resin. The
cross-sectional image showed a clear hexagonalarrangement of uniform mesopores with a large
single crystal-like domain size (at least 500 nm in
width), which indicates a highly aligned structure ofmesochannels parallel to the substrate surface. The
other mesoporous films (MP10-C18, MP30-C18,
MP40-C18, -C14, -C12 and MP50-C12) andpowders (MP10-C18(p) and MP30-C18 (p)) also
showed clear TEM images of hexagonal structure
and one-dimensional channels (Figs. 3-1(a)-(f) and© Toyota Central R&D Labs., Inc. 2014

MP40-C18
Si substrate

Propyl sulfonated mesoporous
silica electrolyte

50nm
Fig. 2
		TEM image of microtome-cut sample forMP40-C18 electrolyte on Si substrate.
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correspond to the capillary condensation into themesopores, and adsorption on the outer surface of themesoporous films, respectively. At medium RH, thewater uptake of the sulfonated mesoporous silica films
was significantly higher, by a factor of two, than thatof Nafion 112 membrane and Nafion thin film. The
onset of capillary condensation shifted to lower RH
upon decreasing pore size or increasing IEC of thesulfonated mesoporous film. The RH shift could be
explained reasonably by the following Kelvin Eq. (4):ln(P/P0) = –2γVm cosθ /(rRT ) ,		

(4)

where P/P0 is a relative vapor pressure at capillary

condensation, γ and Vm are a surface tension and amolecular molar volume of water, respectively, r
is a pore radius, R and T are a gas constant and an
absolute temperature, respectively, and θ is a contact
angle between the pore surface and water molecule.
According to the Kelvin equation, P/P0 becomes small
with decreases in r and θ. The increase in IEC in themesopore surface decreases θ due to the hydrophilic
property of the sulfonic acid group and r due to thebulkiness. Therefore the increase in IEC causes thecapillary condensation at lower RH. Figure 4(c) shows
proton conductivity of the sulfonated mesoporous
films as a function of RH. The proton conductivities
were very high (6.0 × 10–3 – 3.4 × 10–2 S cm–1) at(d) MP40-C14(b) MP30-C18

50nm

50nm

(e) MP40-C12

Fig. 3-1 TEM images of propyl-sulfonated mesoporous silica films; (a) MP10-C18, (b) MP30-C18, (c) MP40-C18,
		 (d) MP40-C14, (e) MP40-C12, (f) MP50-C12 and (g) MP50-C18.

(h) MP10-C18(p)20nm(i) MP30-C18(p)(j) MP50-C18(p)

20nm

20nm

Fig. 3-2 TEM images of propyl-sulfonated mesoporous silica powders; (h) MP10-C18 (p),(i) MP30-C18 (p) and (j) MP50-C18 (p).
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high RH where the mesopores were filled with watercompletely. The proton conductivity jumped anddropped 2-3 orders of magnitude at medium RH in
accordance with the steep increase and decrease inadsorption of water, respectively. RH at the steep
change in proton conductivity shifted lower withthe decrease in pore size and increase in IEC,
which corresponded well with the water vapor
adsorption-desorption isotherms. Thus, the RH
position at the steep change can be controlled by thepore size and the IEC of mesoporous silica according
to the Kelvin equation. Figure 5 shows the relationshipbetween proton diffusion coefficient (Dσ) and water
filling ratio (Fp ) in the mesopores. The Dσ were
calculated using the Nernst-Einstein Eq. (5):Table 1Dσ = kTσ/NHe2 ,				

(5)

NH = (ρIEC/1000)NA ,				

(6)

where k is a Boltzmann’s constant, T is an absolutetemperature, σ is a proton conductivity, NH (Eq. (6)) is aconcentration of the protonic volume calculated fromthe IEC value, e is an electric charge, NA is Avogadro’s
constant, and ρ is a density of the film calculated fromthe weight and the thickness of the film on the substrate.
The Fp were calculated by the following Eq. (7):Fp = Vw /Vp ,					

(7)where Vw and Vp are a volume of adsorbed water andPhysicochemical properties of sulfonic acid mesoporous silica.

SampleMeso
struct.

SBET,
m2·g-1

Pore
Volume,cc·g-1

Pore
Diameter,nm

IEC*,
mmol·g-1

Surface aciddensity,molecules·nm-2

MP10-C18
MP10-C18(p)MP30-C18
MP30-C18(p)MP40-C18
MP40-C14
MP40-C12MP50-C12MP50-C18
MP50-C18(P)

2d-hex2d-hex2d-hex2d-hex2d-hex2d-hex2d-hex2d-hexWormhole
Wormhole

620
1087
756
941
810
910
830
980
390
531

0.51
1.27
0.40
0.78
0.36
0.27
0.26
0.30
0.15
0.61

3.9
3.1
3.4
2.1
3.2
3.0
2.7
2.2
1.7
2.0

0.78 (0.6)
0.47(0.6)
1.52 (1.7)
1.52 (1.7)
1.80 (2.3)
1.82 (2.3)
1.80 (2.3)
2.30 (2.9)
2.25 (2.9)
2.21 (2.9)

0.75
0.22
1.18
0.96
1.34
1.20
1.31
1.41
3.10
2.51

*( ) theoretical IEC

MP30-C18
MP40-C18
MP40-C14
MP40-C14
MP50-C12

Nafion112

5
Nafion thin film

00

Fig. 420
40
60
80
Relative humidity, %

100

0.1

(b)

30
25

Conductivity, S/cm

10

35

(a)
λ = [H2O] / [-SO3H]

λ = [H2O] / [-SO3H]

15

MP10-C18

20
15
10
5
0

Nafion112

0

20
40
60
80
Relative humidity, %

100

(c)

0.01
Nafion112

0.001

MP10-C18
MP30-C18
MP40-C18
MP40-C14
MP40-C12MP50-C120.00010.00001

0

20
40
60
80
Relative humidity, %100

Water uptakes (a), (b) and proton conductivities (c) of propyl-sulfonated mesoporous silica films at 25ºC various
different RH values. Solid and open circles show water adsorption and desorption processes, respectively. Nafion112
and Nafion thin film only water uptakes for adsorption process are shown ((a), (b)).

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R&D Review of Toyota CRDL, Vol.45 No.4 (2014) 59-69

Proton diffusion coeffi. / m2 s-1

MP10-C18
MP30-C18
MP40-C18
MP40-C14
MP40-C12MP50-C12

10-9
10-10
10-11
10-12
10-13

0

0.2

0.4

0.6

0.8

1

Water filling ratio in mesoporesFig. 5(a)Fig. 6(b) Desorption

10-8

MP10-C18
MP30-C18
MP40-C18
MP40-C14
MP40-C12MP50-C12

10-9
10-10
10-11
10-12
10-13

0

0.2

0.4

0.6

0.8

1

Water filling ratio in mesopores

The relationship between proton diffusion coefficient and water filling ratio inmesopores for propyl-sulfonated mesoporous silica films.

a pore volume, respectively. Dσ steeply increased ataround Fp = 0.4 and reached the maxima at Fp = 1
for the mesoporous films except for MP50-C12 andMP10-C18. This indicates that more than 40% fillingof mesopores with water is necessary for exhibiting
high diffusion of protons for mesoporous films withmoderate IEC and pore sizes. Surprisingly, MP50-C12
showed a steep increase in Dσ at around Fp = 0.2. Only
20% filling of mesopores is enough for exhibiting
high proton diffusion. This is mainly attributed to thehigh IEC (2.3 mmol g-1, Table 1). The high IEC canmake proton channels effectives with a smaller amountof water (Fig. 6(a)). MP10-C18 with low IEC(0.78 mmol g-1, Table 1) showed an increase in Dσ
at around Fp = 0.7 because a large amount wateris necessary to make the proton channels effective(Fig. 6(b)).
Figure 7 shows proton conductivities of MP50-C12
at various RHs (90, 50, and 20%) above 25ºC, andArrhenius plots of the conductivities and activationenergies (Ea). The proton conductivities increased
with increasing temperature, and indicated high proton(a)Proton diffusion coeffi. / m2 s-1(a) Adsorption

10-8

(b)

(b)

Water sorption at (a) high and (b) low acid density
at low RH and proton channel formation.

© Toyota Central R&D Labs., Inc. 2014

conductivities of 0.16, 0.11, and 0.0041 S cm–1 for
RH 90, 50, and 20%, respectively at 100°C. The Ea
was obtained by linear regression of an Arrhenius
Eq. (8):σ = σ0exp(–Ea / kbT) ,				

(8)

where σ0 is a pre-exponential parameter and k b is
Boltzmann’s constant. The values of Ea at RH 20, 50,
and 90% were estimated to be 0.26, 0.20, and 0.19 eV,
respectively. These values indicate a Grotthuss
mechanism for the proton conduction. Activationenergy values typically attributed to Grotthuss transfer
via water molecules are in the range of 0.14 – 0.40 eV.(14)The magnitude of Ea decreased with increasing RH,
because water molecules as mobile species wereintroduced.
3. 3 Proton Conductivity under Dry Condition
Figure 8(a) shows proton conductivities of
MP30-C18 and MP50-C18 films with different IEC
above 100ºC, and under dry (RH 0%) or low RH
condition. In Fig. 8, the data for Nafion 112(IEC = 0.9 mmol g-1) and sulfonated polystyrene (SPS)(IEC = 5.37 mmol g-1) measured under dry condition
are shown for comparison. Under dry condition,
proton conductivities of both MP30-C18 and
MP50-C18 increased with increase in temperature.
Comparing the data obtained under dry condition, it
is very clear that proton conductivity of MP50-C18
with high IEC (2.25 mmol g-1) was higher than thatof MP30-C18 (1.52 mmol g-1). Consequently, proton
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R&D Review of Toyota CRDL, Vol.45 No.4 (2014) 59-69

are estimated to be 0.47 and 0.45 eV, respectively,
under dry condition (Fig. 8(b)). This demonstrates
that the increase in the surface acid density in pores
reduce Ea for anhydrous proton transfer. This showsthat the increase in IEC reduces Ea for anhydrous
proton transfer. This also agrees with the results ofthe energy barrier of proton transfer calculated by
the MD simulation.(15) In order to consider the actual
proton transfer in pores, “surface acid density” is more
appropriate than IEC, because the former includes
pore information and the latter does not. Therefore thesurface acid density is used instead of IEC hereafter.
Figure 9 shows detailed atomistic surface models of
the silica walls with various surface acid densities.

conductivity is found to be enhanced by the high IEC
by about two orders of magnitude compared with thatof MP30-C18. Furthermore, the proton conductivityof MP50-C18 was higher than that of Nafion by one
order of magnitude. It is worth noting that MP50-C18
has conductivity comparable to that of SPS, although
the IEC in MP50-C18 is lower than that of SPS(5.37 mmol g-1). This indicates that the continuityof proton pathways for mesoporous electrolyte
is sustained by inorganic pore walls even at hightemperature and low water content allowing for a highproton conductivity, in the case of Nafion and SPS, theproton pathways is almost lost.
The values of Ea for MP30-C18 and MP50-C18

-1

(a)

RH90%

0.1

0.001

40

60

-5

RH20%
Ea=0.26eV
Ea = 0.26eV-70.000120

RH50%
Ea = 0.20eV
Ea=0.20eV

-4
-6

RH20%

0

RH90%
E
Ea=0.19eV
a = 0.19eV

-3

RH50%

0.01

(b)

-2

ln (σ）

Conductivity(σ), S/cm

1

80 100 120

-8
2.5

2.7

Temperature, ºC
Fig. 7
		

(a)

10-3

10-5

-5
RH10%
RH5%

RH0%

SPS (RH 0%)
Nafion (RH 0%)

10-6
10-7

RH0%

100

120

140

Temperature, ºC

Fig. 83.3

3.5(a) Proton conductivities of MP50-C12 at various RH (90, 50, and 20%) above 25ºC and(b) Arrhenius plots of the conductivities and activation energies (Ea) of MP50-C12.

MP50-C18

10-4

3.1

103·T-1, K-1ln(σ, S/cm)

Proton conductivity, S/cm

10-2

2.9

MP30-C18

160

(b)

-7

0.41eV-90.45eV

-11
-13
-15

0.39eV

MP50-C18
SPS (RH0%:0.50eV)

MP30-C18

Nafion (RH0%:0.48eV)

0.47eV

2.2

2.3

2.4

2.5

2.6

2.7

103·T-1, K-1(a) Proton conductivities of various electrolytes under different RH conditions above 100ºC, (b) Arrhenius plots of the
conductivities and activation energies (Ea) of various electrolytes. Ea was estimated from the slope.

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Below 1.5 SO3H molecules nm–2, the sulfonic acidgroups formed hydrogen bonds only to the OH groups
on the silica surface. Above 2.0 SO3H molecules nm–2,
the hydrogen bonds constructed a continuous network
even at 25ºC. This means that the proton conduction
pathways are connected throughout the entire surface
by a hydrogen bond network, resulting in the
suppression of Ea for the proton jumping from one
sulfonic acid site to the nearest neighboring sulfonicacid site even under dry condition. On the other

hand, the values of Ea for Nafion and SPS under dry
condition are 0.48 and 0.50 eV, respectively. These
values are higher than the values for MP30-C18 and
MP50-C18. These data show the importance of proton
channel continuity in the electrolytes. The mesoporous
electrolyte has a rigid silica mesopore backbonethat supports the presence of sulfonic acid groups
at high density within the pores. This construction
allows proton channel continuity in the pores evenunder dry condition, and permits proton transfer with

0.25 SO3H molecules nm–2

0.5 SO3H molecules nm–2

1.0 SO3H molecules nm–2

1.5 SO3H molecules nm–2

2.0 SO3H molecules nm–2

2.5 SO3H molecules nm–2

3.0 SO3H molecules nm–2

4.0 SO3H molecules nm–2

Fig. 9 Atomic surface models on the silica walls with various acid density (0.25-4.0 SO3H molecules nm–2).
© Toyota Central R&D Labs., Inc. 2014

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R&D Review of Toyota CRDL, Vol.45 No.4 (2014) 59-69(≈ 0.4 nm for 2.5 – 3.0 SO3H molecules nm–2) obtainedby the present MD simulations. Based on the resultsof macroscopic proton conductivities for MP50-C18(3.1 SO3H molecules nm–2), the following model is
proposed. Under anhydrous condition, the continuityof the hydrogen bond network is maintained by highdensification of sulfonic acid groups. As for protontransport, proton conduction seems to be related(a)Intensity (arb. units)

lower Ea compared with Nafion and SPS electrolytes.
Based on MD simulations, proton conduction takes
place predominantly via the hydrogen bonds of thesulfonic acid groups. Furthermore, this high proton
conductivity of mesoporous materials is strongly
related to a high density of SO3H groups. Under asmall amount of water, i.e., 5 and 10% RH, proton
conductivity of MP50-C18 was drastically enhanced
compared with the dry condition (Fig. 8). In fact,
proton conductivity was 2 mS/cm at 160˚C in the caseof 10% RH. The magnitude of Ea also decreased withincreasing humidity (0.41 and 0.39 eV for RH 5 and10%), due to added water molecules as proton carriers.
The mesoporous electrolytes loaded with sulfonic acidgroups at high surface acid density are, therefore,
found to promote efficient proton transport even under
low RH conditions.

© Toyota Central R&D Labs., Inc. 2014

0.0012

MP50-pMP50-C18(p)MP30-pMP30-C18(p)MP10-C18(p)MP10-pMSMS

T = 300 K
Q = 0.74673 A−1

Resolution

0.00060

3. 4 Quasielastic Neutron Scattering

-2 0

-10

0

Energy (µeV)

10

20

(b)
Intensity (arb. units)

Figure 10(a) shows the variation of the QENS
spectra with various surface acid densities, namely,
the spectra for MP10 -C18(p), MP30 -C18 (p),MP50-C18(p) and mesoporous silica (MS) without
SO3H groups at 27ºC. It is clear that the QENS
spectrum becomes broad with increasing surfaced aciddensity. From this, we can conclude that broadened
spectra are due to hydrogen motions in sulfonic acid.
The spectrum of MP50-C18(p) with high surface aciddensity of 2.5 SO3H molecules nm-2 at 97ºC is shownin Fig. 10(b) as compared with that at 27ºC. The
QENS spectrum also becomes broad with increasing
temperature. The quasielastic scattering is fitted wellby delta and Lorentz functions (Eq. (2)) convoluted
with instrumental resolution. The Q dependence ofthe obtained full width at half maximum (FWHM)(ΓFWHM (Q)) of the Lorentzian (Eq. (3)) for MP50-C18(p)at 97ºC is shown in Fig. 10(c). The curve is fitted wellby a jump diffusion model. This indicates that the
proton of a sulfonic acid group can self-diffuse even in
the absence of water, as in the case for superprotonic
conductors.(16) A numerical values of proton
self-diffusion coefficient (D), an average diffusion
length (ℓ) and a residence times (τ) obtained from thefitting curve of Fig. 10(c) are 9.11 × 10–6 cm2 sec–1,
0.43 nm and 3.5 × 10–9 sec, respectively. The diffusion
length of proton self-diffusion obtained by QENS
measurements is 0.43 nm, which is consistent with
distance to the nearest neighboring sulfonic acid site0.00180.0016

MP50-C18(p)

97ºCK
370
27ºCK
300

Q = 0.74673 A−1

Resolution

0.0008

0
-20

-10

0

Energy (µeV)

10

20

(c)

Fig. 10 (a) QENS spectra at 27˚C of MP10-C18(p),MP30-C18(p) and MP50-C18(p). (b) Temperaturedependences of QENS spectra of MP50-C18(p).
(c) FWHM v.s. Q for 97˚C of MP50-C18(p) using
a jump diffusion model.
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R&D Review of Toyota CRDL, Vol.45 No.4 (2014) 59-69

to proton self-diffusion of the sulfonic acid groupwithin the hydrogen bond network. It can therefore
be presumed that the distances of proton transport areelongated by increasing the number of neighbors in
the vicinity of the sulfonic acid site. Thus, the highconcentration of hydrogen bonds, which are formedby highly dense sulfonic acid groups, is necessary toincrease anhydrous proton conductivity efficiently.
4. Conclusion
The mesoporous silica electrolytes are of great
advantage in that a large amount of sulfonic acidgroups can be incorporated in the mesopores with noswelling and dissolution properties while preserving
the uniform pore structure. Under hydrated conditions,the proton conductivity increased steeply at medium
RH according to the capillary condensation of waterin the uniform mesopores. The proton conductivities
are enhanced by the high densification of sulfonic acidgroups even at very small amounts of adsorbed water.
Furthermore, under dry condition, the continuityof a hydrogen bond network is built by the highdensification of sulfonic acid groups, and such networkis thought to induce proton hopping conduction between
the neighboring sulfonic acid groups. Such network
presumably enhanced proton transport through thepore channels, resulting in high proton conductivity
at high temperatures. The information gleaned fromthis study will be useful for further understanding of
proton diffusivity in meso-scale channels.
References(1) Steel, B. C. H. and Heintzel, A., Nature, Vol. 414(2001), pp. 345-352.
(2) Kreuer, K. D., Chem. Mater., Vol. 8 (1996),
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(6) Kreuer, K. D., Paddison, S. J., Spohr, E. andSchuster, M., Chem. Rev., Vol. 104 (2004),
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(8) Li, Q., He, R., Jensen, J. O. and Bjerrum, N. J.,
Chem. Mater., Vol. 15 (2003), pp. 4896-4915.
© Toyota Central R&D Labs., Inc. 2014(9) Marschall, R., Rathouský, J. and Wark, M.,
Chem. Mater. Vol. 19 (2007), pp. 6401-6407.
(10) McKeen, J. C., Yan, Y. S. and Davis, M. E.,
Chem. Mater., Vol. 20 (2008), pp. 5122-5124.
(11) Marschall, R., Tölle, P., Cavalcanti, W. L., Wilhelm, M.,
Köhler, C., Frauenheim, T. and Wark, M.,
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(12) Ogawa, G., Chem. Commun. (1996), pp. 1149-1150.
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(14) Colomban P. and Novak, A., Proton Conductors,(1992), pp. 38-55, Cambridge University.
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Köhler, C., Frauenheim, T. and Wark, M.,
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Tyagi, M. and Matsuo, Y., J. Phys. Soc. Jpn., Vol. 79,
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Figs. 1, 2 and 4-7
Reprinted and modified from Chem. Mater., Vol. 25 (2013),
pp. 1584-1591, Fujita, S., Koiwai, A., Kawasumi, M. andInagaki, S., Enhancement of Proton Transport by HighDensification of Sulfonic Acid Groups in Highly Ordered
Mesoporous Silica, © 2013 ACS, with permission from
American Chemical Society.
Figs. 8-10
Reprinted and modified from J. Phys. Chem. C, Vol. 117(2013), pp. 8727-8736, Fujita, S., Kamazawa, K.,
Yamamoto, S., Tygi, M., Araki, T., Sugiyama, J.,
Hasegawa, N. and Kawasumi, M., Proton Conductivity
under Dry Conditions for Mesoporous Silica with
Highly Dense Sulfonic Acid Groups, © 2013 ACS, withpermission from American Chemical Society.
Sections 3.1 and 3.2
Reprinted from Chem. Mater., Vol. 25 (2013),
pp. 1584-1591, Fujita, S., Koiwai, A., Kawasumi, M. andInagaki, S., Enhancement of Proton Transport by HighDensification of Sulfonic Acid Groups in Highly Ordered
Mesoporous Silica, © 2013 ACS, with permission from
American Chemical Society.
Sections 3.3 and 3.4
Reprinted from J. Phys. Chem. C, Vol. 117 (2013),
pp. 8727-8736, Fujita, S., Kamazawa, K., Yamamoto, S.,
Tygi, M., Araki, T., Sugiyama, J., Hasegawa, N. and
Kawasumi, M., Proton Conductivity under Dry Conditionsfor Mesoporous Silica with Highly Dense Sulfonic Acid
Groups, © 2013 ACS, with permission from American
Chemical Society.

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R&D Review of Toyota CRDL, Vol.45 No.4 (2014) 59-69

Satoru Fujita
Research Fields:
		 - Solid State Ionics
		 - Inorganic Chemistry
Academic Degree: Dr.Eng.
Academic Society:		 - The Solid State Ionics Society of Japan

Kazuya Kamazawa
Research Field:
		 - Neutron Scattering Experiments
Academic Degree: Dr.Sci.
Academic Societies:
		 - The Physical Society of Japan		 - The Japanese Society for Neutron Science
Present Affiliation: Comprehensive Research Organization
				for Science and Society

Satoru Yamamoto
Research Fields:
		 - Computational Chemistry for Materials
		 - Rheology of Polymer and Suspension
Academic Degree: Dr.Eng.
Academic Societies:
		 - The Society of Polymer Science, Japan		 - The Society of Rheology Japan
Awards:		 - R&D 100 Award (Fillers Flow), 1999
		 - Research Award of the Soc. of Rheology Japan, 2001
Present Affiliation: Dassault Systemes Biovia K. K.

Akihiko Koiwai
Research Fields:
		 - Materials Science		 - Fuel Cell
Academic Societies:
		 - The Chemical Society of Japan		 - The Society of Polymer Science, Japan

Shinji Inagaki
Research Field:
		 - Synthesis and Applications of		 Mesoporous Materials
Academic Degree: Ph.D.
Academic Societies:
		 - The Chemical Society of Japan		 - Catalysis Society of Japan		 - Japan Association of Zeolite		 - The Japan Society on Adsorption
		 - The Society of Polymer Science, Japan		 - International Mesostructured Materials Association
		 - International Zeolite Association
Awards:		 - The Award of Chemistry on Catalyst Preparation,
		 1994		 - The Promotion Award of the Japan Society on
		 Adsorption, 2001
		 - The Chemical Society of Japan Award for Creative		 Work, 2004
		 - The Minister Award of Education, Culture, Sport,
		 Science and Technology, 2005
		 - The Japan Society on Adsorption Award, 2008

Jun Sugiyama
Research Field:
		 - Materials Analysis using Muons and		 Neutrons
Academic Degree: Dr.Eng.
Academic Societies:
		 - Physical Society of Japan		 - American Physical Society		 - Society of Muon and Meson Science of Japan		 - International Society for mSR Spectroscopy
		 - The Japanese Society for Neutron ScienceAwards:		 - Best Poster Award of International Conference on
		 Neutron Scattering, 2013
		 - World Young Fellow Meeting Presentation Award of
		 The Ceramic Society of Japan, 2004

Masaya Kawasumi
Research Fields:
		 - Fuel Cell
		 - Macromolecular Science		 - Polymer Synthesis
Academic Degree: Ph.D.
Academic Societies:
		 - The Chemical Society of Japan		 - The Society of Polymer Science, Japan		 - The Electrochemical Society of Japan
Awards:		 - The Award of the Society of Polymer Science, Japan,
		 2009		 - The Society of Silicon Chemistry Japan Award, 2007
© Toyota Central R&D Labs., Inc. 2014

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