Publicado en Electrochimica Acta 54 (2009) 2239–2245.
Ruthenium oxide/carbon composites having a microporous carbon or a mesoporous
carbon as support. A comparative study as supercapacitor electrodes.
F. Picoa, E. Morales b, J.A. Fernandez, T.A. Centenoc, J. Ibánezd, R.M. Rojasa, J.M.
Amarillaa, J.M. Rojoa
a. Instituto de Ciencia de Materiales de Madrid (ICMM), Consejo Superior de
Investigaciones Científicas (CSIC), Sor Juana Inés de la Cruz, Cantoblanco, 28049Madrid, Spain.
b. Instituto Nacional del Carbon (INCAR), CSIC, Francisco Pintado Fe, 33011-Oviedo,
Spain.
c. Instituto de Ciencia y Tecnología de Polímeros (ICTP), CSIC, Juan de la Cierva 3,
28006-Madrid, Spain.
d. Centro Nacional de Investigaciones Metalúrgicas (CENIM), CSIC, Avda. Gregorio
del Amo 8, E-28040-Madrid, Spain
0
Abstract
Composites have been prepared by depositing nanoparticles of RuO2.xH2O (1-5 nm) on
two carbons: a microporous carbon (1.3 nm of pore size) and a mesoporous carbon (11
nm of pore size). The composites have been obtained by two ways: (i) way A consisting
of an accumulative impregnation treatment of the carbons with RuCl3.0.5H2O solution,
and (ii) way B consisting of a impregnation of the carbons with Ru(acac)3 vapour. The
way B leads to supported RuO2.xH2O particles that appear more crystalline and more
heterogeneous in size than those obtained by way A. Specific surface area and specific
capacitance of the composites have been measured. The two magnitudes, which are
analysed as a function of the RuO2 content, show very different dependences for the
composites derived from the two carbons. They are discussed on the basis of the size of
the supported RuO2.xH2O particles in comparison to the size of the carbon pores.
Key words: ruthenium oxide, microporous carbon, mesoporous carbon, electrodes,
supercapacitors.
1
1. Introduction
Composites made from particles of ruthenium oxide (usually named
RuO2.xH2O) deposited on a carbon have been prepared since the pioneer work by Miller
et al. [1], in order to combine the high pseudocapacitance (also called redox-type
capacitance) of RuO2.xH2O with the double-layer capacitance of the carbon. By this
way electrodes showing specific capacitances higher than those of bare carbons have
been prepared. The electrodes have been prepared from: (i) carbons with different
porosity and different specific surface areas, e.g. carbon aerogel [--], activated carbons
[--], mesopore-templated carbon [--], carbon black [--], carbon nanotubes [--], carbon
nanofibres [--], etc., (ii) different reagents as sources of RuO2.xH2O, e.g. RuCl3.0.5H2O
or Ru(acac)3, and hence different procedures: a sol-gel followed of neutralization in the
case of RuCl3.0.5H2O and an electrochemical oxidation in the case of Ru(acac)3, and
(iii) different contents (loadings) of RuO2.xH2O in the composite. These three points
have raised a great difficulty in comparing the composites already reported, and as a
consequence of the lack of comparison some questions remain opened. For instance,
what is the carbon and the procedure that lead to a better dispersion of the RuO2.xH2O
particles, or how varies the capacitance of the RuO2.xH2O/carbon composites for
RuO2.xH2O particles of different sizes. The later point is of particular importance
because the pseudocapacitance of RuO2.xH2O comes mainly from the outer part of its
particles [--]. In some ruthenium oxide/carbon composites a specific capacitance for
RuO2.xH2O as high as 1000 F/g, i.e. even higher than that of bare RuO2.xH2O (720 F/g)
2
[27], has been reported [7,9,10,15,19,22]. Then small particles of RuO2.xH2O seem to
show a higher specific capacitance and hence its contribution to the specific capacitance
of the composites can be higher. Other point to be considered is the porosity and
specific surface area of the carbon acting as support. Porosity and surface area account
for the specific capacitance of the carbons. Because they can change with the
progressive deposition of the RuO2.xH2O particles, the contribution of the carbon to the
specific capacitance of the composite can change with the loading of RuO2.xH2O.
In order to get a better understanding on the carbon-supported RuO2 composites,
we have compared in this work composites having two carbons as supports: a
microporous carbon and a mesoporous carbon. The composites have been prepared
from two ruthenium sources (either ruthenium chloride or ruthenium acetylacetonate)
and by two procedures (liquid impregnation followed by neutralization or vapor
impregnation followed by air oxidation). The composites have been checked as
electrodes in two-electrode supercapacitor cells, and their specific capacitance has been
discussed on the basis of the composite surface area, carbon pore size and RuO2.xH2O
particle size.
2. Experimental
The carbons used as supports were two commercial carbons: (i) microporous
M30 carbon from Osaka Gas with average pore size of 1.3 nm, and (ii) mesoporous
Monarch 1400 carbon from Cabot with average pore size of 11 nm. The microporous
carbon and the mesoporous one are hereafter labeled Micro C and Meso C, respectively.
Ruthenium oxide was obtained from two reagents: ruthenium III chloride
(RuCl3.0.5H2O from Aldrich) and ruthenium III acetylacetonate (Ru(acac)3 or Ru(CH3CO-CH-CO-CH3)3 from Aldrich as well).
3
Two ways were followed to obtain the composites:
Way A: 0.5 g of each carbon, either Micro C or Meso C, was dispersed in 50 ml
of an aqueous 0.034 M RuCl3.0.5H2O solution under continuous stirring for 24 h. In
some particular cases, and in order to get impregnations with lower contents in
RuCl3.0.5H2O, lower concentrations of the RuCl3.0.5H2O solution (either 0.0015 or
0.003 M) were used such as other authors did [8]. In all cases the dispersions were
filtered to remove the RuCl3.0.5H2O solution excess and to get carbons impregnated
with RuCl3.0.5H2O. Then the impregnated carbons were added to 50 ml of aqueous 10-4
M NaOH solution and the pH was measured. Drop wise of another 0.01 M NaOH
solution was added to neutralize the dispersion (up to pH=7). Then formation of
RuO2.xH2O happened. The dispersions were filtered and the solids (composites) were
collected. They were washed with distilled water up to negative chloride test. Then the
composites were dried at 80 ºC overnight. Accumulative treatments consisting of
impregnations of both Micro C or Meso C with the 0.034 M RuCl3.0.5H2O solution
followed by filtering and neutralization allowed us obtaining composites with higher
loadings in RuO2.xH2O. All composites were heat-treated at 120 ºC for 90 min.
A sample of bare RuO2.xH2O was also prepared by adding drop wise of 0.01 M
NaOH solution on 50 ml of 0.034 M RuCl3.H2O solution; the added volume of the 0.01
M NaOH solution was that needed to increase the pH solution up to pH=7. The solid
obtained, i.e. RuO2.xH2O, was washed with distilled water and then air-dried at room
temperature. The sample was heat-treated at 120 ºC for 90 min.
Way B: Mixtures of carbon (either Micro C or Meso C) and Ru(acac)3 their
mass being taken in different proportions were heated under vacuum at 190 ºC for 2 h; it
allowed infiltration of Ru(acac)3 into the carbon pores. Subsequent treatment in Ar-flow
at 320 ºC for 2 h allowed transformation of Ru(acac)3 into Ru metal. Then, air-flow
4
treatment at 120 ºC for 90 min transformed the ruthenium metal into ruthenium oxide.
A sample of bare ruthenium oxide could not be prepared by way B; the solid obtained
had in part Ru metal.
We should note that all the composites obtained either by way A or by way B
were heat-treated at the same temperature (120 ºC) for the same time (90 min).
Thermogravimetric (TG) analyses were carried out in air-flow (50 ml/min) at a
heating rate of 5 ºC/min with Stanton STA 781 instrument. In all cases the mass of the
composite was of ca. 10 mg.
Powder X-ray diffraction (XRD) patterns were recorded at room temperature in
D-8 Bruker diffractometer, with Cu K radiation. The XRD patterns were obtained in
the step scanning mode of 0.02º (2) and 1 s/step counting time, within the range
10270º.
Nitrogen
adsorption/desorption
isotherms
were
recorded
at
77
K
using….CONTINUAR Teresa
Transmission electron micrographs (TEMs) were taken in Jeol JEM 3000 F field
emission microscope operating at acceleration voltage of 300 kV. The samples were
dispersed in n-butyl alcohol, and drops of the dispersions were transferred to carboncoated copper grids.
Supercapacitor electrodes were processed as cylindrical pellets of 13 mm
diameter and ca. 1 mm height. The composites together with the polymer PVDF (20 wt
%) and carbon black (5 wt %) were mixed in a mortar and then compacted under cold
pressure of ???? 150 MPa. Supercapacitors were assembled in two-electrode
SwagelokTM-type cells. The two cylindrical electrodes were separated by a glassy
microfibre paper (Whatman 934 AH). Aqueous 2M H2SO4 solution was chosen as
electrolyte. Two tantalum rods acted as current collectors. Charge and discharge of the
5
supercapacitor cells were tested by galvanostatic measurements at room temperature on
PGSTAT30 Autolab potentiostat/galvanostat.
3. Results and discussion
3.1 Structural and thermal characterization.
XRD patterns of the RuO2.xH2O/Meso C composites obtained by the ways A
and B and then heat-treated at 120 ºC for 90 min are shown as examples in Fig. 1. We
see broad diffractions lines (arrow marked) whose positions coincide with reflections
(002) and (101) of the mesoporous carbon used as support. After heating the composites
at 600 ºC, the XRD pattern shows typical reflections of crystalline RuO 2 (rutile-type
structure). It confirms that RuO2.xH2O had been deposited on the Meso C. In the
patterns of the composites obtained by the ways A and B, and heated at 120 ºC, the lack
of reflections ascribable to crystalline RuO2 indicates that the supported ruthenium
oxide is amorphous (usually named RuO2.xH2O).
Bare ruthenium oxide obtained by way A showed a XRD pattern that is typical
of an amorphous material (pattern not shown). However the sample obtained by way B
showed a XRD pattern (patterns not shown) with some broad peaks ascribable to an
amorphous, presumably ruthenium oxide, together with some peaks ascribable to Ru
metal. So, this sample is in part ruthenium oxide and in part Ru metal.
The air-flow TG curves recorded on two RuO2.xH2O/Meso C composites having
different load in RuO2.xH2O and both obtained by way A are shown in Fig. 2 as
examples. In this figure the TG curves of the Meso C and bare RuO2.xH2O are included
as references. We see a significant weight loss of Meso C at about 600 ºC that is due to
the carbon combustion. The low residue (weight % at the plateau observed between 600
and 800 ºC) accounts for a low ash content of Meso C. In the TG curves of the
6
composites we see a sharp weight loss and a residue. The weight loss is due to the
combustion of Meso C. Moreover, we see that the combustion temperature decreases as
the amount of supported RuO2 increases; it agrees with the fact that RuO2 catalyses
combustion of carbons [12,37]. The residues at the high-temperature plateaus are
ascribed to ash from Meso C plus crystalline RuO2; the presence of RuO2 has been
evidenced by XRD, whose pattern is similar to that shown in Fig. 1 for the composite
heated at 600 ºC. Taking into account the weight of the residue of the starting Meso C
and the weight of the residues of the composites, the RuO2 content in each composite
has been deduced; these contents are outlined in Table 1. In Fig. 2 the TG curve of bare
RuO2.xH2O (obtained by way A) shows: (i) a weight loss up to 150 ºC that is ascribed
to removal of adsorbed water without crystallization of the oxide, (ii) a plateau between
150 and 250 ºC, and (iii) another small weight loss above 250 ºC due to removal of
additional water; this weight loss is accompanied by crystallization of the amorphous
RuO2.xH2O into crystalline RuO2, the latter showing a rutile-type structure [27].
3.2 Morphological and textural characterization.
TEM images of two composites obtained by the ways A and B, with Meso C as
support and with the same load in RuO2 (15 wt %), are shown as examples in Fig. 3.
The particle size of the supported RuO2.xH2O is similar in both cases ranging 1-5 nm.
However we see that the RuO2.xH2O particles are more crystalline in the composite
obtained by way B (Fig. 3b) compared with the composite obtained by way A (Fig. 3a).
Indeed, the lattice planes of the RuO2.xH2O particles are better distinguished in Fig. 3b.
The electron diffraction rings and electron diffraction spots, which are ascribed to the
rutile-type RuO2, but not to Ru metal, are better distinguished in the composite obtained
by way B (see the insets in Fig. 3). The composites obtained by way A show all the
RuO2.xH2O particles with sizes in the range 1-5 nm; the average particle size increases
7
in this range as the RuO2 content increases from 2 to 15 wt %. The composites obtained
by way B show together with the RuO2.xH2O particles of 1-5 nm size some other
particles of larger size (10 nm and even more). Therefore, the way B leads to
RuO2.xH2O particles that are more crystalline and more heterogeneous in size compared
to way A.
Nitrogen adsorption/desorption isotherms of Micro C and Meso C as well as of
two composites having these carbons as supports are shown in Fig. 4a. The two
composites were obtained by way A. We see that for Micro C and its derived composite
the isotherm is of type I, which correspond to microporous solids. Moreover, the total
adsorbed nitrogen volume is lower in the composite compared to bare Micro C. For
Meso C and its derived composite the isotherm is of type II. At low relative pressures
(P/P0<0.1) the sharp adsorptions indicate the presence of some micropores. At
intermediate relative pressures (P/P0 = 0.4-0.7) and at high relative pressures (P/P0>0.7)
the hysteresis loops confirm the presence of mesopores. The total adsorbed volume is
lower for the composite compared to bare Meso C. Similar isotherms have been
obtained for the composites prepared by the way B. For the composites obtained by the
two ways we have determined the specific surface area (SBET).
Variation of SBET vs. RuO2 content is shown in Fig. 4b for the composites
obtained from Micro C (triangles) or Meso C (circles) and by way A (open symbols) or
way B (closed symbols). For the Micro C-derived composites (open and closed
triangles) the experimental values depart from the straight line, the latter accounting for
the rule of mixtures according to the equation:
SBET= (100-) (SBET)1/100 + (SBET)2/100
(1)
where  stands for the weight percentage of RuO2, (100-) stands for the weight
percentage of Micro C, (SBET)1 stands for the specific surface area of Micro C, and
8
(SBET)2 stands for the specific surface area of bare RuO2. The lower values of the
experimental SBET (open and closed triangles) compared to the predicted SBET (dashed
line) suggest a significant blocking of the carbon micropores by the deposited
RuO2.xH2O particles. It agrees with the larger size (1-5 nm) of the deposited
RuO2.xH2O particles compared to the average pore size (1.3 nm) of the Micro C.
Regarding the Meso C-derived composites (open and closed circles), their SBET
decreases linearly as the RuO2 content increases (Fig. 4b). This dependence agrees with
an equation similar to eq. (1) and indicates that the decrease in specific surface area of
the composites is a consequence of the lower surface area of RuO2.xH2O compared to
Meso C. In these composites the carbon surface is progressively covered by the
deposited RuO2.xH2O particles but the latter do not block the carbon mesopores because
the RuO2.xH2O particles (1-5 nm) are smaller than the carbon mesopores (11 nm).
3.3 Electrochemical characterization.
Charge/discharge galvanostatic plot (voltage vs. time) obtained at 20 mA/cm2 is
shown as an example in Fig. 5a. At the beginning of the charge and the discharge we
see a sharp change in voltage (V1) from which the equivalent series resistance (ESR) of
the supercapacitor cell can be determined according to V1 =2xIxESR. Capacitance of
the cell has been measured along the discharge process according to C=Ixtd/V2, where
td and V2 stand for the discharge time and voltage decrement, respectively. The
capacitance (Ce) of each electrode is Ce=2C, in accordance with the series arrangement
of the two electrodes within the cell. From Ce and the mass of the active electrode (i.e.
the mass of the Micro C or Meso C, the mass of the composites or the mass of the bare
RuO2.xH2O), the specific capacitance (in F/g) has been calculated. Variation of the
specific capacitance vs. the current density is shown in Fig. 5b. In all samples the
specific capacitance decreases slightly with increasing current density as usual.
9
Moreover we see an increase in the specific capacitance of the composites as the RuO 2
content increases.
The specific capacitance measured at a low current density (1 mA/cm2), i.e. in
nearly steady-state, as a function of the RuO2 content has been plotted in Fig. 6 for the
composites obtained from Micro C (triangles) or Meso C (circles), and prepared by the
way A (open symbols) or way B (closed symbols). For Meso C-derived composites
obtained by way A (open circles) the specific capacitance increases linearly as the RuO2
content increases according to equation:
Csp=(100-) (Csp)1/100 + (Csp)2/100
(2)
where  stands for the RuO2 weight percentage as already mentioned, (100-) stands
for the carbon weight percentage (Meso C), (Csp)1 stands for the specific capacitance of
Meso C, and (Csp)2 stands for the specific capacitance of bare RuO2.xH2O. The fitting
by a straight line indicates that the specific capacitance of the composites holds the rule
of mixtures, i.e. the composites behave like a mixture of two components: Meso C and
RuO2.xH2O. The specific capacitance of the composites obtained by way B (see closed
circles) seems also to follow a linear dependence. The extrapolation of the straight line
at 100 wt% RuO2 leads to a specific capacitance of ca. 350 F/g for bare RuO2.xH2O.
Unfortunately this value could not be experimentally confirmed because the difficulty
of obtaining bare RuO2.xH2O by way B. The value expected for bare RuO2.xH2O
obtained by way B (350 F/g) is clearly lower than the value measured for bare
RuO2.xH2O obtained by way A (650 F/g). The lower specific capacitance of the former
accounts for the lower specific capacitance of the composites obtained by way B, and it
agrees with the fact that the supported RuO2.xH2O particles are more crystalline as
already discussed. The specific capacitance of amorphous RuO2.xH2O decreases as it is
crystallized [-----]. If the contribution of RuO2.xH2O to the specific capacitance of the
10
composites is lower, the composites must show lower specific capacitances as
experimentally found.
For Micro C-derived composites obtained by way A (open triangles) or way B
(closed triangles), the specific capacitance remains nearly constant as the RuO2 content
increases. This fact suggest that the increase in the specific capacitance of the
composites due to the progressive increase in the RuO2 content is compensated by some
anomalous decrease due to the carbon contribution. To check this point we have
calculated the specific capacitance of the composites as the sum of two contributions:
one contribution from Micro C and another one from RuO2.xH2O. The carbon
contribution has been estimated taking into account the capacitance per surface area
(C/SBET ratio) of Micro C that is equal to 8.7 F/cm2, and the specific surface areas
(SBET) of the composites as taken from Fig. 4b. The assumption of taking composite SBET
= Micro C SBET can be accepted because of the larger SBET of Micro C (2300 m2/g)
compared to SBET of bare RuO2.xH2O (69 m2/g). The ruthenium oxide contribution has
been estimated from the specific capacitance of bare RuO2.xH2O (650 F/g), and its
relative content in each composite. The calculated specific capacitance of the
composites (see aterisks in Fig. 6) agree with the experimental values (open and closed
triangles in the same figure). Therefore, the nearly constant specific capacitance of
Micro C-derived composites comes from a compensation between the increase in
specific capacitance due to the contribution of RuO2.xH2O and the decrease in specific
capacitance due the contribution of Micro C, the latter being associated with blocking of
the carbon micropores by the supported RuO2.xH2O particles as already discussed.
For the Meso C-derived composites in which the specific capacitance follows
the rule of mixtures according to eq. (2), the specific capacitance of supported
RuO2.xH2O has been deduced from this equation. This magnitude has been plotted as a
11
function of the RuO2 content (Fig. 7) for the composites obtained by way A (open
circles) and way B (closed circles). The plot, which is similar to that reported for
RuO2.xH2O/carbon nanofibres composites [--] shows two regions: region I in which the
RuO2.xH2O specific capacitance decreases as RuO2 content increases, and region II in
which RuO2.xH2O specific capacitance is constant. In region I the decrease in
capacitance can be associated with an increase in the RuO2.xH2O particle size [---].
Indeed we have found by TEM that the particle size increases from 1 nm to 5 nm for the
composites included in this region. In region II the nearly constant specific capacitance
of RuO2.xH2O is associated with an increase in the amount of deposited RuO2.xH2O
particles [---], but the particle size of the supported RuO2.xH2O remains constant (4-5
nm). Comparing the two preparation ways we see that the plateau of region II is higher
for way A (ca. 600 F/g) than for way B (ca. 350 F/g). This indicates a lower specific
capacitance of the RuO2.xH2O particles deposited by way B in agreement with the fact
that the supported RuO2.xH2O particles are more crystalline as already discussed.
Finally, we have checked the cycle life of the composites that is rather high. For
instance, the two-electrode supercapacitor cell having as active electrode material the
composite RuO2.xH2O/Meso C (with 15.4 wt % RuO2 and obtained by way A) was
cycled at a current density of 100 mA/cm2. After 10,000 charge/discharge cycles the
capacitance had only decreased by 11%.
4. Conclusion
Composites consisting of RuO2.xH2O particles deposited on two carbons, one of
them microporous carbon and the other mesoporous carbon, have been prepared by two
ways: (i) way A consisting of an accumulative treatment of impregnation of the carbons
with RuCl3.0.5H2O solution, filtering to remove RuCl3.0.5H2O excess and
12
neutralization with NaOH solution to get RuO2.xH2O, and (ii) way B consisting of
impregnation of the carbons with Ru(acac)3, followed by heating in inert atmosphere to
transform Ru(acac)3 into Ru metal, and then heating in air to oxidize Ru metal to
amorphous RuO2.xH2O. Way B leads to RuO2.xH2O particles that appear more
crystalline and more heterogeneous in size as compared to those obtained by way A.
From the point of view of the specific capacitance RuO2.xH2O deposited by way A is
more efficient as compared to that deposited by way B.
The work shows the importance of the particle size of the deposited RuO2.xH2O
particles in relation to the pore size of the carbons acting as supports. Thus in
RuO2.xH2O/Meso C composites the smaller size of the supported particles compared to
the carbon pores accounts for a decrease in specific surface area of the composites in
agreement with the rule of mixtures. In these composites the specific capacitance
increases as the RuO2.xH2O load increases. However in RuO2.xH2O/Micro C
composites in which the RuO2.xH2O particles block the carbon pores, a significant
decrease in specific surface area has been found. In these composites the specific
capacitance is nearly constant because the increase in capacitance due to the progressive
increase in RuO2.xH2O load is compensated by a decrease in the carbon contribution
due to a decrease in carbon surface area.
Acknowledgement
Financial support through the project of reference MAT2005-01606 is gratefully
acknowledged. F. Pico thanks for a contract associated with that project.
13
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FIGURE CAPTIONS
Figure 1. X-ray diffraction patterns recorded at room temperature on bare mesoporous
carbon (Meso C) and on two derived composites with similar RuO2 contents but
obtained by way A or way B. The pattern of the composite obtained by way A and heattreated at 600 ºC (rutile-type RuO2 pattern) is shown as a reference.
Figure 2. Air-flow thermogravimetric (TG) analyses of two composites derived from
Meso C and obtained by way A. The TG curves recorded on bare Meso C as well as on
bare RuO2.xH2O are shown as references.
Figure 3. TEM images of two composites having Meso C as support and the same RuO2
content (15.4 wt %) but the composites were obtained by way A (a) and way B(b).
Some supported RuO2.xH2O particles are arrow marked. Electron diffractions are
shown in their respective insets.
Figure 4. (a) Nitrogen adsorption/desorption isotherms recorded on the carbons Micro C
and Meso C as well as on two composites using these carbons as supports and prepared
by way A. (b) Dependence of the BET specific surface area of the composites as a
function of the RuO2 content. Dashed lines are the expected dependences according to
eq. (1). Triangles stand for the composites having Micro C as support. Circles stand for
the composites having Meso C as support. Open and closed symbols stand for the
composites prepared by way A and way B, respectively.
17
Figure 5. (a) Galvanostatic charge/discharge plot recorded at 20 mA/cm2 for a
composite having Meso C as support and RuO2 content of 15.4 wt %. (b) Dependence
of the specific capacitance of some composites prepared by way A, having Meso C as
support and the RuO2 contents: 5.8 wt % (open circles), 11.3 wt % (open triangles) and
15.4 wt % (open squares). The dependences found for Meso C (closed circles) and bare
RuO2.xH2O (closed squares) are shown as references.
Figure 6. Specific capacitance of the composites vs. RuO2 content. Circles stand for the
composites having Meso C as support. Triangles stand for the composites having Micro
C as support. Open symbols and closed symbols stand for the composites obtained by
way A and way B, respectively. Asterisks stand for the specific capacitance calculated
as described in the text.
Figure 7. RuO2.xH2O specific capacitance (in Farads per gram of RuO2) vs. RuO2
content for composites having Meso C as support. Open and closed circles stand for the
composites obtained by way A and way B, respectively. Solid lines are guides to the
eye. Dashed line separates region I from region II.
18
(110)
(110)
(101)
(211)
15.4 wt % RuO2
way A, 600 ºC
(200)
(111)
15.0 wt % RuO2
way B, 120ºC
15.4 wt % RuO2
way A, 120 ºC
(002)
(101)
(004)
10
20
30
40
50
2 (degrees)
60
Meso C
120 ºC
70
Figure 1
100
RuO2. xH2O
Mass (%)
80
60
40
15.4 wt % RuO2
20
5.8 wt % RuO2
0
Meso C
0
200
400
600
800
1000
Temperature (ºC)
19
Figure 2
20
Figure 3a
Figure 3b
21
Volume adsorbed (cm STP/g)
1000
Micro C
3
800
Micro C-7.3 wt % RuO2
way A
600
400
Meso C
200
Meso C-15.4 wt % RuO2
way A
0
0.0
0.2
0.4
0.6
0.8
1.0
P/P0
Figure 4a
2500
Way A MON-RuO2
Way B MON-RuO2
Way B Enrique MON-RuO2
Way A M30-RuO2
Way B M30-RuO2
Way B Enrique M30-RuO2
2
Composite's SBET (m /g)
2000
1500
1000
500
0
0
20
40
60
80
100
RuO2 content (wt.%)
Figure 4b
22
1.0
V1
2
20 mA/cm
e
rg
0.6
arg
ch
ch
a
di s
e
Voltage (V)
0.8
V2
0.4
0.2
td
0.0
0
20
40
60
80
100
Time (s)
Figure 5a
Specific capacitance (F/g)
500
400
300
150
100
50
0
0
100
200
300
2
Current density (mA/cm )
Figure 5b
23
Composite's specific capacitance (F/g)
700
WayA M30-RuO2
WayB M30-RuO2
WayA MONARCH-RuO2
WayB MONARCH-RuO2
WayB Enrique MONARCH-RuO2
WayB Enrique M30-RuO2
RuO2 puro 120ºC 90'
600
500
400
300
200
100
0
0
20
40
60
80
100
RuO2 content (wt %)
RuO2.xH2O specific capacitance (F/g)
Figure 6
1000
2Cesp RuO2 en MON wayA
2Cesp RuO2 en MON Enrique
2Cesp RuO2 en MON wayB
800
600
400
200
region I
region II
0
0
20
40
60
80
100
RuO2 content (wt %)
Figure 7
24