Mesoporous

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Effect of Mesopore Ordering in Otherwise Similar Micro/Mesoporous Carbons on the High-Rate Performance of Electric Double-Layer Capacitors Karthik Mani, Edurne Redondo, Eider Goikolea, Vladimir V. Roddatis, Stefania Doppiu, and Roman Mysyk J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/jp508581x • Publication Date (Web): 12 Nov 2014 Downloaded from http://pubs.acs.org on November 21, 2014

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The Journal of Physical Chemistry

Effect of Mesopore Ordering in Otherwise Similar Micro/Mesoporous Carbons on the High-Rate Performance of Electric Double-Layer Capacitors Mani Karthik, Edurne Redondo, Eider Goikolea, Vladimir Roddatis, Stefania Doppiu, Roman Mysyk* CIC Energigune, C/Albert Einstein 48, 01510 Miñano, Spain

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ABSTRACT We probed the effect of structural mesopore ordering on the rate performance of supercapacitors using two carbon materials differing mainly in the ordering of mesopores, but displaying the same micropore size distributions, similar mesopore size distributions, and similar electrical conductivity. The material with ordered mesopores shows an excellent rate capability of ~ 80 % capacitance retention at a very high current density of 50 A g-1, whereas its disordered counterpart exhibits a capacitance retention of ~ 60 % at the same current density. On account of the similarities between the two carbons, the enhanced rate capability of highly ordered mesoporous carbon can be attributed to the straight channels of long-range highly ordered 2D hexagonal mesopores. This provides favorable conditions for ultrafast ion transport, suggesting the role of mesopores in high-rate operation to be more important than being an electrolyte reservoir only.

KEYWORDS: supercapacitors, rate performance, micropores, ordered mesopores.

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1.

Introduction

Electrochemical energy storage systems represent one of the viable solutions to reducing the world’s dependence on fossil energy sources. Among these systems, electrochemical doublelayer capacitors occupy a specific niche between batteries and electrolytic capacitors in terms of the “energy-to-power” relationship, delivering energy within a few seconds and featuring much higher cycling ability than batteries. This originates inherently from their operating principle, which is the electrosorption of ions from electrolyte onto high-surface-area electrodes without making and breaking chemical bonds. Nanoporous activated carbon (AC) electrode materials provide the best trade-off between performance and cost, although carbons in more fashionable forms such as template carbons,1 carbon onions,2 and very recently graphene3 have also been extensively investigated, providing in some cases significant improvements in performance over activated carbons. However, the availability of nanoporous carbons makes them the most ubiquitous electrode material in a foreseeable future, and their textural properties are one of the most critical factors impacting the specific energy and power of electrochemical capacitors (ECs). More specifically, the capacitance and the rate performance of ECs are greatly dependent on electrolyte access into electrode pores.4,5 Thus, favorable conditions for rapid ion transport should be provided, which requires minimizing the tortuosity of pore networks and adapting the size and shape of pores in carbon materials to those of electrolyte ions6. However, these parameters are relatively difficult to control in conventional preparation methods such as physical or chemical activation. However, the capacitance and especially the rate capability of ECs can presumably be greatly enhanced by using ordered carbons, which enables better control over pore size and shape, leading to the effectively accessible electrode/electrolyte interface area being maintained at high charge/discharge rate.1 Several studies underline the beneficial effect of

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pore ordering on the rate performance of supercapacitors.1,

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However, ordered carbons are

often contrasted with conventional activated carbons, greatly differing from their ordered counterparts in properties such as electrical conductivity, pore size distribution, specific surface area, etc, which are not accounted for in such kind of comparative work, but play a nonnegligible role in the rate performance of supercapacitors. For instance, Kyotani et al.1 demonstrated a noticeable difference in the rate capability of two ordered microporous template carbons with similarly-sized pores, but different electrical conductivities. Thus, a single property of otherwise similar nanoporous carbon materials can be of decisive importance to the rate performance of ECs. In this study, we focus on another parameter, which is mesopore ordering and its effect on the high-rate performance of supercapacitors, intentionally keeping all other carbon properties as similar as possible. This specific question arises because the capacitance and rate performance of ECs are commonly believed to depend greatly on micropore features such as specific surface area, pore size, length and tortuosity, whereas mesopores, being significantly larger than ions, are considered to act mostly as an electrolyte supply to micropores.10 To achieve fair comparison, we consider the rate performance of two mesoporous carbons prepared by the hydrothermal low-temperature autoclaving method using resorcinol and formaldehyde as the carbon precursors and Pluronic F127 as the structure-directing template.11 The order and disorder of mesopores are induced by adjusting the F/R molar ratio.

2. Experimental Section 2.1. Preparation of carbons. Resorcinol (4.125 g) and Pluronic F127 (6.25 g) were dissolved in a 1:1 mixture of water and ethanol (~100 mL) and the mixture was stirred for 15 min. 37 wt. % hydrochloric acid (0.5 g) was added to the mixture and stirred for 1 h. 37 wt. % formaldehyde solution (3.125 g or 6.25 g) was added dropwise under stirring, and the reaction mixture was

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stirred for another hour until a homogeneous solution was obtained. The solution was transferred into a polypropylene bottle kept in a hot air oven at 50 ºC for 4 days. After hydrothermal treatment, polymeric monoliths were collected by filtration and dried in an oven at 50 ºC for 12 h and subsequently at 80 °C for another 12 h. After the two-step heating process, the color of the polymeric monoliths changed into dark reddish. Finally, mesoporous carbon monoliths were obtained by carbonization of the polymeric monoliths at 1000 oC for 1h under N2 stream in a tubular furnace at a heating rate of 1ºC min-1. The resulting mesoporous carbon material was denoted as MC-x (x represents the F/R ratio: 1 or 2).

2.2. Characterization of samples. For all the carbon samples, N2 adsorption-desorption isotherms were measured at 77 K using a surface area analyzer (Micromeritics, ASAP 2020). Prior to the measurements, the carbons were degassed at 350 ºC under vacuum (10-3 mbar) for 6 h. The specific surface area (SSA) was calculated by the Brunauer-Emmett-Teller method (BET) and the 2D Non-Local Density Functional Theory (2D NLDFT). The last was also used to derive the pore size distribution using data reduction software SAEIUS.12 The average pore size was calculated from the DFT data separately for the microporous and mesoporous regions according to the formula:

V max

L0 =

∫

V min

LdV (1)

Vmax −Vmin

where L0 is the average pore size, L is the pore size at the current value of pore volume, Vmin and Vmax are correspondingly the maximum and the minimum values of the cumulative pore volume in the studied pore size region. Transmission electron microscopy (TEM) and high resolution

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transmission electron microscopy (HRTEM) measurements were carried out by using a FEI Tecnai F20 electron microscope operating at 200 keV and equipped with a High Angle Annular Dark Field (HAADF) detector and Energy Dispersive X-ray (EDX) spectrometer. For the TEM measurements, all carbon samples were ground with acetone and the resulting sample dispersions of the powder carbon samples were transferred onto a holey carbon film fixed on a 3 mm copper grid (200 mesh). Electron diffraction patterns were collected using the selected area electron diffraction (SAED) technique. Small-angle X-ray scattering (SAXS) patterns of all the samples were recorded in the 2θ range of 0-5° by using a Nanostar small-angle X-ray scattering instrument (Bruker) with Cu Kr radiation (40 kV, 35 mA). The electrical conductivity of carbons was measured in air at room temperature by the Van der Pauw four-probe technique. Electrical contacts were made using Pt wires and Ag paste placed over whole end faces ensuring a homogeneous current flow. The conductivity (σ) was determined from a set of V–I values by taking σ = 1/ρ = l/A × dI/dV, where l is the distance between voltage contacts and A is the sample cross section. A current load of 25–100 mA was applied with a Keithley 6221 DC and AC current source. The corresponding voltage drop was recorded with a 2182A nanovoltimeter. The electrical conductivities of the highly ordered and disordered mesoporous carbon monoliths present no substantial difference and are 21.03 S cm-1 and 17.96 S cm-1, respectively. 2.3. Electrochemical performance. Electrodes were prepared by mixing a carbon material (95 wt. %) and a polytetrafluorethylene (PTFE) binder (5 wt. %, from a 60 wt. % aqueous dispersion). The mixture was homogenized by adding a few milliliters of ethanol and then worked out until plasticity. The plastic composite was then rolled to a thickness of ~200 µm and dried under vacuum at 120 oC overnight. Disk-shaped electrodes of 11 mm in diameter were then

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cut out, weighted and their thickness was measured again. The final thickness of the electrodes was 190 ± 10 µm while the mass loading was 10.5 mg cm-2. Figure 1 shows a schematic of the cell configuration used in this study. Briefly, two-electrode supercapacitor cells were assembled within a Teflon Swagelok® airtight system using two identical carbon electrodes, two stainless steel current collectors, a porous glass fibre membrane separator (Whatman GFB). 6M KOH or 1M H2SO4 were used as electrolyte solution. A mercury/mercury oxide reference electrode (Hg/HgO in 0.1M KOH) was introduced into the alkali-based two-electrode cells for discriminating between the potential evolution of each of the two electrodes with the scan rate and the cut-off voltage being imposed between the positive and negative electrodes.

Figure 1. Schematic of the Swagelok cell assembly.

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Cyclic voltammetry (CV) and galvanostatic (GA) charge-discharge cycling measurements were conducted using a multichannel VMP3 generator (Biologic). Electrochemical impedance spectroscopy (EIS) measurements were conducted by applying a low sinusoidal amplitude alternating voltage of 10 mV at frequencies from 1 MHz to 10 mHz using the same instrument. Gravimetric capacitance per electrode was calculated on the basis of the GA measurements from the below formula: C = 2∫Idt/(∆Vmam)

(2)

where C is the gravimetric capacitance per electrode (F g-1), Idt the differential charge (A s), ∆V the cell voltage (V), mam the mass of active material per electrode (g). The capacitance values are reported for the voltage range between 0 V and the maximum voltage of the cell, excluding the Ohmic drop. The differential gravimetric capacitance in the CV experiments was calculated per electrode from the formula: C = 2I/[(dV/dt) mam]

(3)

where C is the gravimetric capacitance per electrode (F g-1), I the current (A), dV/dt the scan rate (V s-1), mam the mass of electrode active material (g). The capacitance of the positive and negative electrodes can be separately calculated from the potential change at the corresponding electrode. For instance, in case of the positive electrode: C+ =

∫ I dt

(4)

∆E + m +

where C+ is the capacitance of the positive electrode (F g-1), ∆E+ its potential range, m+ its mass. The statistical relevance of the results was verified by comparing the electrochemical response of 3 identical cells, i.e. six electrodes per each type of carbon. The variation among parallel measurements did not exceed 5 %.

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3. Results and Discussion 3.1. Texture of carbons with ordered and disordered mesoporous. Textural properties such as SSA (BET), specific pore volume and average pore size derived from N2 adsorptiondesorption measurements are summarized in Table 1.

Table 1. Textural properties of carbon samples Sample

F/R

SBET

SNLDFT (m2/g)

Micropore volume (cm3/g)

Mesopore volume (cm3/g)

(m2/g)

Average micropore size (nm)

Average mesopore size (nm)

MC-1

1

619

718

0.183

0.378

0.77

4.09

MC-2

2

673

616

0.166

0.275

0.78

3.75

As shown in Figure 2a, sample MC-1 clearly exhibits type I and IV isotherms according to the IUPAC classification. 13, 14 The initial portion of the isotherms at low P/Po values (10-7 to 10-5) corresponds to micropore volume filling (type I), which is followed by a narrow step due to N2 capillary condensation within the mesopores (type IV).

13, 14

The isotherms also display clear

hysteresis loops at P/Po values between 0.4 and 0.8 for sample MC-1, which is indicative of the mesoporosity. By contrast, although the N2 adsorption-desorption isotherms of sample MC-2 obtained with an F/R = 2 are also classified as type I and IV, there are noticeable differences in the shape of the capillary hysteresis loops shown in Figure 2. Further analysis of the adsorption isotherms can be provided with the 2D-NLDFT approach for MC-1 and MC-2 samples (Figure 2b). Both materials clearly show a bimodal pore size distribution exhibiting two distinct maxima in the micropores and mesopores regions. Two 9



characteristic features can be discerned: i) the mesopore size distribution lies within ∼ 2 nm

500

3

-1

Adsorbed volume (cm g )

independently of ordering, ii) the micropore size distribution is nearly the same for both carbons.

3

(a)

400 300 MC-1

200 MC-2

100 0 0.0

0.2

0.4

0.6

0.8

1.0

Relative pressure (P/P0) 0.4 (b)

-1

-1

Diff. pore volume (cm nm g )

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MC-1

0.3

MC-2

0.2 0.1 0.0

0

1

2

3

4

5

6

Pore size (nm) Figure 2. Textural characterization of MC-1 (blue) and MC-2 (black) mesoporous carbon materials: (a) nitrogen adsorption-desorption isotherms and (b) 2D-NLDFT pore size distributions. The structural morphology of the mesoporous carbons was further analyzed by TEM. The TEM images of the mesoporous carbon samples are shown in Figure 3, displaying a well ordered longrange hexagonal arrangement of mesostructured material MC-1 viewed along the [001] and

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[110] directions (Figures 3a and 3b, respectively). The TEM images of sample MC-2 (Figures 3c and 3d) reveal the loss of long-range crystallographic order, clearly evidencing the presence of highly disordered mesostructured materials. The results of TEM confirm that the F/R molar ratio exercises a major influence on the ordering of the resulting mesoporous carbons, in agreement with the results of Liu et al.11 This conclusion is supported by the SAXS patterns acquired over a larger fraction of the sample (see Figure S1 and the corresponding description in the Supporting information).

58.7º

Figure 3. TEM images with low (a,c) and high (b,d) magnifications of ordered MC-1 (a,b) and disordered MC-2 (c,d) mesoporous carbons.

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3.2. Electrochemical performance. As evidenced by the adsorption and TEM measurements, the highly ordered MC-1 and disordered MC-2 carbons differ mainly in mesopore ordering, and are therefore good candidates to specifically probe the effect of mesopore ordering on the rate capability of supercapacitors. However, both carbons unavoidably contain some microporosity, which is known to greatly impact the rate performance. Most importantly, the accessibility of electrolyte ions into comparably sized pores is strongly hindered, which adversely affects the capacitance at high current. With the intention of reducing the limitations brought in by a possibly close match between ion size and micropore size, aqueous KOH electrolyte was selected because of the small size of its ions (less than 0.5 nm, see in more detail below) as compared to the average micropore size of about 0.8 nm (see Figure 2) of MC-1 and MC-2. Therefore, the selected electrode material/electrolyte couples should provide the best conditions to specifically study the effect of mesopore organization on the rate performance. Notably, the capacitive performance of the ordered mesoporous material was recently reported for the scan rates up to 100 mV s-1 together with that of derived materials prepared through additional oxidative treatment to increase the capacitance by Faradaic pseudocapacitive contribution.

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However, this work concentrated on increasing capacitance through surface functionalization and the effect of mesopore ordering was not explicitly investigated. Figure 4 shows the CVs of both mesoporous carbons in a broad range of scan rates (5 to 500 mV s-1) in 6M KOH electrolyte. Noteworthy, all the CVs show typical capacitive behavior characterized by a rectangular shape even at 500 mV s-1, and the ordered material exhibits a 30 % higher capacitance, approximately in accordance to the DFT SSA (∼20 % higher SSA for MC-1).

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Capacitance ( F g-1)

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MC-1

100

MC-2

50 0 -50 -100 0.0

0.2

0.4

0.6

0.8

1.0

Cell voltage (V) Figure 4. Cyclic voltammogramms of supercapacitors built with 6M KOH electrolyte and mesoporous carbons, correspondingly ordered MC-1 (blue curves) and disordered MC-2 (black curves) at scan rates of 100, 200 and 500 mV s-1. Arrows point to the direction of increasing scan rate. The behavior of ions in micropores can be elucidated by the electrochemical response of the individual electrodes displayed in Figures 5a and 5b for both carbons at 5 mV s-1, evidencing a larger potential evolution at the positive electrode where charge storage is preferentially associated with electrosorption of hydroxyl anions. The explanation for the slightly unequal potential range can be derived from the equivalence of the charges built up in the positive (Q+) and negative (Q-) electrodes, i.e. Q+ = Q-, which can be rewritten as C+ ∆E+ m+ = C- ∆E- m-

(5)

C+ is the capacitance, ∆E+ the potential range, m+ the mass of the positive electrode, C- , ∆E-, mthe corresponding values for the negative electrode.

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-1

Current density (mA g )

400

Electrode Potential (V vs. Hg/HgO) -0.8 -0.6 -0.4 -0.2 0

Electrode Potential (V vs. Hg/HgO) -0.8 -0.6 -0.4 -0.2 0 0.2

(a)

(c)

200 0 -200 MC-1 -1 5 mV s

-400 0

-2

-1

Current density x10 (mA g )

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200

0.2

0.4 0.6 0.8 Cell Voltage (V)

1

MC-2 -1 5 mV s

0

0.2


1


Electrode Potential (V vs. Hg/HgO) -1 -0.8 -0.6 -0.4 -0.2 0

(b)

(d)

100 0 -100 MC-1 -1 500 mV s

-200 0

0.2


1

MC-2 -1 500 mV s

0

0.2


1

Figure 5. Cell voltage (blue and black lines) vs. potential evolution of individual electrodes at slow and fast charge/discharge: positive electrode in red and negative electrode in green. Cyclic voltammogramms at 5 mv.s-1 (a and c for MC-1 and MC-2, correspondingly) and at 500 mv.s-1 (b and d for MC-1 and MC-2, correspondingly). Considering the equal electrode masses in a symmetric supercapacitor cell, the lower capacitance of the positive electrode becomes evident (C+ = 73 F g-1 vs C- = 108 F g-1 for MC-1 and C+ = 56 F g-1 vs C- = 85 F g-1 for MC-2), which in turn implies a lower portion of the electrode surface

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accessible to OH- ions. Since monovalent K+ cations are electrosorbed in the hydrated state and their effective size lies between 0.362 and 0.420 nm, 16 this indicates that OH- ions are bigger than K+ ions (as also evidenced recently17) and are also electrosorbed in the hydrated state, unlike other monovalent anions such as Cl- or NO3-. 16 It is also noticeable that this effect holds for both the ordered and disordered materials, which points to the similar accessibility of electrolyte ions to the narrowest micropores of both carbons. By contrast, the potential range of both electrodes is very similar at 500 mV s-1, indicating the equal capacitance of the positive and negative electrodes (Figures 5c and 5d). In turn, this infers a similar portion of the surface to be accessible to both cations and anions at high scan rates due to hindered ion access into the narrowest pores. Thus, the minor difference in the capacitance of cations and anions disappears at a practically significant charge/discharge rate, and, most importantly, this effect is common for both ordered and disordered carbons (Figures 5c and 5d). Thus, any possible trend in capacitance decay at high current density should be influenced by the effect of large accessible pores only. This observation can be more rigorously explored from the evolution of the electrochemical capacitance measured in the constant current charge/discharge experiments. In these measurements, the rate performance was additionally probed in 1M H2SO4 electrolyte to ensure that not only is the observed trend specific to KOH, but it can also be extended to a larger range of electrolytes. The data are presented on a normalized scale to make the comparison of rate capabilities meaningful as the absolute values of capacitance depend on the specific surface area according to the well-known formula C=ε0εS/d where ε0 is the dielectric constant, ε the dielectric permittivity, S the effective specific surface area, d the charge separation.

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The value of capacitance retention, C/C0, where C0 is the capacitance at 0.1 A.g-1, is thus used to specifically follow the evolution of capacitance with discharge rate without considering the absolute capacitance values. Figure 6a shows clearly that the capacitance decay is weaker for the ordered mesoporous carbon in both electrolytes, 6M KOH and 1M H2SO4, which is beneficial for the rate capability of ECs and can well be associated with the presence of mesopore ordering, enhancing ion diffusion. Additionally, the higher mesopore volume of MC-1 can also favor its better rate performance. Furthermore, it is remarkable that the ordered mesoporous material is able to maintain ∼ 80 % of its initial capacitance in KOH electrolyte at a very high current density of 50 A g-1 in contrast to the 60 % capacitance retention of the disordered MC-2 sample. Nyquist plots (Figure S3) also show that MC-1 based cells better approach the theoretical vertical line (indicative of an “ideal” capacitor), which is in agreement with the constant current experiments, showing better capacitance retention at high rate, i.e. the electrochemically accessible surface at high rate is higher for MC-1 than for MC-2 based cells. Figure 6b shows the dependence of the capacitance on the discharge time, which can be valuable in assessing the percentage of low-rate capacitance available to a specific high-rate application. Again, one can easily notice that MC-1 keeps up to about 80 % of its initial capacitance in KOH electrolyte at a discharge time of about 1 s, i.e. exactly in the time domain of applications where current and envisioned market demand for supercapacitors is strongest.

16


100 90 80 70 60

MC-1, 6M KOH MC-1, 1M H2SO4

50


(a) 40

10

20

30

40

50

Discharge time (s) Capacitance retention (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Capacitance retention (%)

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100

75

50 MC-4d-1, 6M KOH MC-4d-1, 1M H2SO4

25

MC-4d-2, 6M KOH MC-4d-2, 1M H2SO4

(b) 0 0

10

20

30

40

50

-1

Current density (A g )

Figure 6. Capacitance retention vs current density (a) and discharge time (b) for MC-1 and MC2 samples in aqueous 6M KOH and 1M H2SO4 electrolytes Also from the viewpoint of applications, the cycling performance of MC-1 laboratory cells is nearly perfect, presenting 95 % of capacitance retention in H2SO4 after 10000 cycles and ~ 4 % increase of capacitance in KOH after also 10000 cycles. The latter can result from slightly enhanced electrolyte penetration into the smallest micropores upon cycling and/or an additional minor charge storage capability due to some extra pseudocapacitance.

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4. Conclusions The extremely different mesopore architecture of two carbons prepared by changing the parameters of the same hydrothermal process clearly demonstrated the beneficial effect of mesopore structural ordering on the rate performance of supercapacitors. Rigorous comparison is made possible since the materials were synthesized by the same procedure and from the same parent reactants, which has allowed the rate capability of supercapacitor cells to be minimally influenced by all other factors except for mesopore ordering. The relation between mesopore organization and the rate response of supercapacitors suggests the role of mesopores to be more important than merely being an electrolyte reservoir. This is especially true for high discharge current, i.e. in a practically significant time domain of supercapacitor applications. From the practical point of view, highly ordered mesoporous carbon has shown good rate capability at very high current density of 50 A g-1, which confirms its suitability for those applications where high-rate response is at a premium. AUTHOR INFORMATION

Corresponding Author *E-mail: [email protected]. Tel: +34 945 297 108 ACKNOWLEDGMENT The research leading to these results has received funding from the European Community’s Seventh Framework Programme [FP7/2007-2013] under grant agreement no 296006 and from the Basque Government under the Etortek Energigune'12 Program. The authors thank Dr. Julie Ségalini, Dr. Damien Saurel and Naira Soguero Perez for experimental assistance.

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REFERENCES (1) Itoi, H.; Nishihara, H.; Kogure, T.; Kyotani, T. Three-dimensionally arrayed and mutually connected 1.2-nm nanopores for high-performance electric double layer capacitor. J. Am. Chem. Soc. 2011, 133, 1165-1167. (2) Gao, Y.; Zhou, Y. S.; Qian, M.; He, X. N.; Redepenning, J.; Goodman, P.; Li, H. M.; Jiang, L.; Lu, Y. F. Chemical activation of carbon nano-onions for high-rate supercapacitor electrodes. Carbon 2013, 51, 52-58. (3) Zhu, Y.; Murali, S.; Stoller, M. D.; Ganesh, K. J.; Cai, W.; Ferreira, P. J.; Pirkle, A.; Wallace, R. M.; Cychosz, K. A.; Thommes, M.; et al. Carbon-based supercapacitors produced by activation of graphene, Science 2011, 332, 1537-1541. (4) Conway, B. E. Electrochemical Supercapacitors: Scientific Fundamentals and Technological Applications; Kluwer: Amsterdam, Netherlands, 1999, 411-429. (5) Kötz, R.; Carlen, M. Principles and applications of electrochemical capacitors. Electrochimica Acta 2000, 45, 2483-2498. (6) Bleda-Martínez, M. J.; Lozano-Castelló, D.; Cazorla-Amorós, D.; Morallón, E. Kinetics of double layer formation: influence of porous structure and pore size distribution. Energy Fuels,

2010, 24, 3378-3384. (7) Tsai, W.-Y.; Gao, P.-C.; Daffos, B.; Taberna, P.-L.; Perez, C. R.; Gogotsi, Y.; Favier, F.; Simon, P. Ordered mesoporous silicon carbide-derived carbon for high-power supercapacitors. Electrochem. Comm. 2013, 34, 109–112.

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(8) Xing, W.; Qiao, S.Z.; Ding, R.G.; Li, F.; Lu, G.Q.; Yan, Z.F.; Cheng, H.M. Superior electric double layer capacitors using ordered mesoporous carbons. Carbon 2006, 44, 216–224. (9) Wang, J.; Xue, C.; Lv, Y.; Zhang, F. Kilogram-scale synthesis of ordered mesoporous carbons and their electrochemical performance. Carbon 2011, 49, 4580–4588. (10) Vix-Guterl, C.; Frackowiak, E.; Jurewicz, K.; Friebe, M.; Parmentier, J.; Béguin, F. Electrochemical energy storage in ordered porous carbon materials. Carbon 2005, 43, 12931302. (11) Liu, L.; Wang, F.-Y.; Shao, G.-S.; Yuan, Z.-Y. A low-temperature autoclaving route to synthesize monolithic carbon materials with an ordered mesostructure. Carbon 2010, 48, 20892099. (12) Jagiello, J.; Oliver, J. P. 2D-NLDFT adsorption models for carbon slit-shaped pores with surface energetical heterogeneity and geometrical corrugation. Carbon 2013, 55, 70-80. (13) Wang, X. Q.; Liang, C. D.; Dai, S. Facile synthesis of ordered mesoporous carbons with high thermal stability by self-assembly of resorcinol−formaldehyde and block copolymers under highly acidic conditions. Langmuir 2008, 24, 7500-7505. (14) Meng, Y.; Gu, D.; Zhang, F.; Shi, Y.; Cheng, L.; Feng, D.; Wu, Z.; Chen, Z.; Wan, Y.; et al. A family of highly ordered mesoporous polymer resin and carbon structures from organicorganic self-assembly. Chem. Mater. 2006, 18, 4447-4464. (15) Ren, T.-Z.; Liu, L.; Zhang, Y.; Yuan Z.-Y. Nitric acid oxidation of ordered mesoporous carbons for use in electrochemical supercapacitors. J. Solid State Electrochem. 2013, 17, 22232233.

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(16) Eliad, L.; Salitra, G.; Soffer, A.; Aurbach D. Ion sieving effects in the electrical double layer of porous carbon electrodes: estimating effective ion size in electrolytic solutions. J. Phys. Chem. B. 2001, 105, 6880-6887. (17) Garcia-Gomez, A.; Barranco, V.; Moreno-Fernandez, G.; Ibañez, J; Centeno, T. A.; Rojo, J. M. Correlation between capacitance and porosity in microporous carbon monoliths. J. Phys. Chem. C. 2014, 118, 5134-5141.

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Table of Contents (TOC) Image.


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 29

100 75 50 25 0 0

10 20 30 40 Current density (A g-1)

50

22


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


Ref. electrode

Page 23 of 29

Current collector SS plunger

+ Separator Whatman Glass Fiber B soaked in 6M KOH or 1M H2SO4

Electrolyte 6M KOH (aq) or 1M H2SO4 (aq)

Electrodes (95 wt.% Carbon. 5 wt.% PTFE)


3

-1

500

Page 24 of 29

(a)

400 300 MC-1

200 MC-2

100 0 0.0

0.2

0.4

0.6

0.8

1.0

Relative pressure (P/P0) 0.4

3

-1

-1

Diff. pore volume (cm nm g )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

Adsorbed volume (cm g )


(b)

MC-1

0.3

MC-2

0.2 0.1 0.0

0

1

2

3

4

Pore size (nm)


5

6

Page 25 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


58.7º


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

Capacitance ( F g-1)


Page 26 of 29

MC-1

100

MC-2

50 0 -50 -100 0.0

0.2

0.4

0.6

Cell voltage (V)


0.8

1.0

Electrode Potential (V vs. Hg/HgO) -0.8 -0.6 -0.4 -0.2 0 400 (a)

Electrode Potential (V vs. Hg/HgO) -0.8 -0.6 -0.4 -0.2 0 0.2 (c)

200 0 -200 MC-1 -1 5 mV s

-400 0

Current density x10-2 (mA g-1 )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


Current density (mA g -1)

Page 27 of 29

200

0.2


1

MC-2 -1 5 mV s

0

0.2


1


Electrode Potential (V vs. Hg/HgO) -1 -0.8 -0.6 -0.4 -0.2 0

(b)

(d)

100 0 -100 MC-1 -1 500 mV s

-200 0

0.2

MC-2 -1 500 mV s

0.2 0.4 0.6 0.8 0.4 0.6 0.8 1 0 ACS Paragon Plus Environment Cell Voltage (V) Cell Voltage (V)

1

Page 28 of 29

100 90 80 70 60


50


(a) 40

10

20

30

40

50

Discharge time (s)


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42



100

75

50 MC-4d-1, 6M KOH MC-4d-1, 1M H2SO4

25

MC-4d-2, 6M KOH MC-4d-2, 1M H2SO4

(b) 0

0

10

20

30

40 -1

Current density (A g )


50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42



Page 29 of 29

100 75 50 25 0 0

10 20 30 40 Current density (A g-1)


50

Mesoporous

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