Graphitic Mesoporous Carbons with Embedded Prussian Blue

Subscriber access provided by The Open University

Article

Graphitic mesoporous carbons with embedded Prussian blue-derived iron oxide nanoparticles synthesized by soft-templating and low temperature graphitization Nilantha P Wickramaratne, Vindya S Perera, Byung-Wook Park, Min Gao, Grant W McGimpsey, Songping D. Huang, and Mietek Jaroniec Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/cm401124d • Publication Date (Web): 19 Jun 2013 Downloaded from http://pubs.acs.org on June 19, 2013

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Chemistry of Materials is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 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 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Chemistry of Materials

Graphitic mesoporous carbons with embedded Prussian blue-derived iron oxide nanoparticles synthesized by soft-templating and low temperature graphitization Nilantha P. Wickramaratne,† Vindya S. Perera,† Byung-Wook Park,† Min Gao,‡ Grant W. McGimpsey,† Songping D. Huang,† and Mietek Jaroniec∗,†

†

Department of Chemistry, Kent State University, Kent, Ohio 44242, USA. ‡

Liquid Crystal Institute, Kent State University, Kent, OH,44242,USA. E-mail: [email protected]

RECEIVED DATE: ABSTRACT A series of highly graphitized mesoporous carbons was synthesized by self-assembly of polymeric carbon precursors and block copolymer template in the presence of poly(vinylpyrrolidone) (PVP) coated Prussian blue (PB) nanoparticles used as a graphitization catalyst. Resorcinol and formaldehyde were used as carbon precursors, poly(ethylene oxide) – poly(propylene oxide) – poly(ethylene oxide) triblock copolymer (Pluronic F127) was employed as a soft template. The carbon precursors were polymerized in hydrophilic domains of block copolymer along with PVP-coated PB nanoparticles, followed by

∗

Corresponding [email protected].

author:

(Jaroniec)

Phone:

330-672-3790;

ACS Paragon Plus Environment

Fax:

330-672-3816;

E-mail:

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 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 22

carbonization. This recipe gave carbons with cylindrical mesopores created by thermal decomposition of the soft template, and with PB-derived iron oxide nanoparticles. In addition, the presence of iron species catalyzed graphitization at relatively low temperature. The XRD and TEM measurements revealed that the resulting carbons obtained with smaller amounts of PB exhibited ordered mesostructures with relatively high degree of graphitization; however, exceedingly graphitic carbons with disordered mesopores were obtained with higher amounts of PB. Further, wide angle XRD measurements and TGA analysis provided evidence that graphitization took place at 600 oC, which is considered as a very low temperature for graphitization process. N2 adsorption and TGA analysis showed that the aforementioned carbons exhibited high surface area (reaching 621 m2/g) and extremely high percentage of graphitic domains (approaching 87 %). Interestingly, the carbon prepared with larger amount of PB showed magnetic properties. Electrochemical measurements performed on these carbons for double layer capacitors showed somewhat rectangular shape of cyclic voltammetry (CV) curves with a large capacitance of 211 F/g in 1M H2SO4 electrolyte. KEYWORDS: Low temperature graphitization, Magnetic carbon, Supercapacitors, Graphitic carbons, ordered mesoporous carbons

TOC GRAPHICS


2

Page 3 of 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 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION The versatility of mesoporous graphitic carbons makes them very attractive for a number of applications including lithium-ion batteries,1 fuel cells,2,3 supercapacitors,4 adsorption5,6

as well as catalyst

supports.7,8 In terms of adsorption applications, it is essential to synthesize carbon materials with high surface area, well developed microporosity and mesoporosity. In the last few years, magnetically separable mesoporous graphitic carbons are vastly studied for adsorption of various dyes, phenols, and heavy metals.5,9,10 The advantage of a magnetically separable carbon is in its easy isolation from the solution with a magnet. However, other applications require carbons that are electric conductive, thermally stable, possess high specific surface area, well developed microporosity and mesoporosity. Recently, mesoporous graphitic carbons attracted much attention as supercapacitor electrode materials due to a unique combination of chemical and physical properties, namely: high conductivity, high surface area, good corrosion resistance, excellent thermal stability in inert atmosphere, controlled pore structure, and most importantly, low cost.11 The presence of large volume of both micropores and mesopores in the carbon material is critical for the development of high power supercapacitors. The energy storage in supercapacitors is based on the storage and release of charges between double-layer formed at the electrode/electrolyte interface. Thus, the energy storage is strongly dependent on the surface area, derived mainly from micropores of the electrode materials. There are two well-known methods that have been mainly used for the preparation of carbons with a large fraction of micropores; namely activation12,13

and tetraethyl orthosilicate (TEOS)-assisted generation of micropores .14,15

Further, it was also shown that mesopores ensure fast ion transport to micropores and active sites, and facilitate the formation of double layer, which is essential for the development of high power supercapacitors.16-18In addition to those factors, the electrical conductivity of carbon is indispensable for high power supercapacitors. Conductivity of carbon materials increases with the degree of


3


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 4 of 22

graphitization. Therefore, the carbon electrode materials with high degree of graphitization and suitable porous structure are needed for achieving high energy storage capacity. There are three major methods for the synthesis of mesoporous graphitic carbons: (1) high temperature chemical vapor deposition (CVD),1 (2) high temperature or/and high pressure treatment of carbon precursors,19-21 and (3) catalytic graphitization .22 Among them, catalytic graphitization processes gained much attention because they can be carried out at lower temperatures, about 900 oC, which reduces the cost of graphitic carbon materials. So far, the hard templating catalytic graphitization has been employed for the synthesis of mesoporous graphitic carbons in the presence of various catalysts such as Fe, Co, Mn, and Ni.4,22-24 Numerous hard templates such as colloidal silica,7 mesoporous metal oxides,25 SBA-15,26 CaCO3 nanospheres, polymer nanospheres4 and porous zeolites along with graphitization catalysts were studied to obtain mesoporous graphitic carbons. A typical synthesis includes the preparation of a hard template, filling it with carbon precursors and catalysts, thermal treatment at high temperatures, and finally removal of the template by dissolution or thermal treatment. The aforementioned nanocasting method is time consuming, expensive, and complicated; thus, it is unfeasible from industrial viewpoint. In contrast, soft templating combined with catalytic graphitization simplifies the synthesis of mesoporous graphitic carbons.27 Wenjun et al. 28 reported the synthesis of mesoporous graphitic carbons in the presence of Fe(NO3)3·9H2O salt, which acts as a graphitization catalyst. Also, Li et al. 29 reported the synthesis of partially graphitic mesoporous carbon using the soft templating strategy. However, these ordered mesoporous carbons possessed smaller percentage of graphitic domains (3 nm; w – mesopore width at the maximum of PSD.

Thermogravimetric analysis. TGA was used to analyze the amount of incorporated Fe species (TG residue at 800 oC) and to estimate the degree of graphitization in the carbons studied. It was shown that graphitized carbon shows higher thermal stability in air than amorphous carbons. Therefore, the percentages of amorphous and graphitic forms of carbon can be estimated by TG analysis in flowing air. As can be seen in Figure 2, the TG profiles show two distinct weight losses at 400-500 and 500-600 oC. The corresponding DTG peaks to the aforementioned weight losses can be assigned to the oxidation of amorphous and graphitic carbon, respectively. The percentage of graphitic carbon in the sample can be simply measured by using the weight loss percentage obtained from the TG profile: ACS Paragon Plus Environment

9


%

graphitic carbon weight loss % x 100 graphitic + amorphous carbon weight loss %

As shown in Figure 2A and Table 1, the graphitic carbon percentage (GC %) can be simply tuned by varying the amount of PB in the synthesis mixture. These data show that the carbon samples obtained at higher concentration of PB (60 mM solution) exhibited very high graphitization degrees, about 87 %. Simply, by increasing the volume of PB solution from 1 to 2, and 3 mL one can vary the GC % from 13 to 48, and 83 for the carbons obtained at 900 oC. However, the GC % did not change much when the PB volume increased from 3 to 5mL; for instance, compare the values of GC % for CPB*4-9 and CPB*5-9 with that for CPB*3-9. These data suggest that there is an optimal amount of PB that assures the maximum GC % (about 87 %); this means that the further increase in the amount of PB in the synthesis mixture does not change GC %. 100

60

8 4

40

0 450

500

550

600

Temperature (o C)

20

CPB3-9 CPB4-9 CPB5-9

8

60 4

40 0 400

A

450

500

550

Temperature (o C)

600

20

B

0 0

200

400

600

80

W eight (% )

12

80

W eight (% )

o

CPB*1-9 CPB*2-9 CPB*3-9 CPB*4-9 CPB*5-9

16

-Derivative weight (% / o C )

100

-Derivative weight (%/ C)

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 10 of 22

0 0

200

400

600

Temperature (oC)

Temperature (oC)

Figure 2. Weight change (TG) and differential weight change (DTG, inset) profiles for CPB* (A) and CPB (B) carbons obtained at 900 oC.

Interestingly, the TG profiles also reveal the presence of high percentage of graphitic domains in the CPB* carbons obtained at lower carbonization temperatures. Namely, the CPB*4-7 and CPB*5-7 samples exhibited ~82% of graphitic carbon (see Figure S1). This value is quite similar to 87% that was obtained for carbons graphitized at higher temperatures, for instance at 900 oC. Analysis of the TG data indicates that for the aforementioned samples a nearly complete catalytic graphitization occurred at 700


10

Page 11 of 22


o

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

C. It appears that the obtained GC percentages are the highest ever reported values for the carbons

graphitized at both 700 and 900 oC. However, somewhat lower GC % was obtained for CPB*3-7 as compared to that evaluated for CPB*3-9. This result indicates that the optimal amount of catalyst is needed for achieving the maximum degree of graphitization. Also, the crystalinity of thermally treated carbons at 600 oC was examined; note that CPB*4-6 and CPB*5-6 possessed comparatively small percentages of graphitic domains, reaching 4 and 13 %, respectively (see Figure S2). Meanwhile, CPB*3-6 did not show any graphitic nature, indicating the amount of the catalyst used was insufficient for graphitization at low temperatures. To the best of our knowledge this is the first report dealing with catalytic graphitization of phenolic resin-based carbons at 600 oC; note that the carbon contribution arising from the PVP used was estimated to be very small (see Figure S3 and provided analysis in supporting information). As shown in Figure 2B, the maximum graphitic carbon percentage obtained for CPB series is about ~43% for CPB-5-9. Unlike in the previous case, this set of carbons exhibited comparatively small percentages of graphitic domains ranging from 31 to 43 %. It is obvious that the CPB* series of the samples was obtained by using twice larger amount of PB catalyst as compared to the amount of PB used in the synthesis of CPB carbons. It is noteworthy that the oxidation temperature ranges reported in this study are slightly lower than the oxidation temperature ranges 450-600 and 600-750 reported for amorphous and graphitic carbons, respectively. 28,34,35 The main reason for the observed lower oxidation temperature ranges for amorphous and graphitic carbons is the presence of potassium in PB. It was found that the potassium containing oxides and silicates act as an catalyst for oxidation of carbons.36 To show the catalytic behavior of potassium for the carbon oxidation, the TG profiles were recorded for assynthesized CPB*4-9 sample as well as for the samples obtained by washing CPB*4-9 with water and 2M HCl. As shown in Figure. S4, the oxidation temperatures for amorphous and graphitic portions of the as-synthesized CPB*4-9 carbon (note that this sample showed the highest potassium content) are 350 and 450 oC, while higher temperatures, 500 and 600 oC, were obtained for the HCl-treated CPB*4-9


11


carbon, respectively. This result shows clearly the catalytic effect of potassium on the decrease of temperature for oxidation of amorphous and graphitic carbons. CPB*1-9 CPB*2-9 CPB*3-9 CPB*4-9 CPB*5-9

intensity (arb.units)

A

0.5

1.0

1.5

2.0

2.5

3.0

Degree (2θ)

B

20

40

C

60


CPB*1-9 CPB*2-9 CPB*3-9 CPB*4-9 CPB*5-9


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 12 of 22

80

20

Degree (2θ)

40

CPB3-9 CPB4-9 CPB5-9

60

80

Degree (2θ)

Figure 3. Small angle XRD measurements for CPB* samples (A), and wide angle XRD measurements for CPB* (B) and CPB (C) carbons obtained at 900 oC.

X-Ray diffraction (XRD) studies. The small-angle and wide-angle XRD measurements were used to examine mesoporosity and crystallinity of the samples studied, respectively. The presence of a distinct peak at 2θ = 0.90-0.95 (small angle range) for the first two carbons of the CPB*-9 series, CPB*1-9 and CPB*2-9, can be associated with uniform mesopores (see Figure 3A); TEM analysis of these samples revealed the presence of ordered mesopores (see next section). For both samples, the d-spacing value corresponding to the aforementioned XRD peak is equal to 10.4 nm. Similarly, the small angle XRD patterns for the CPB5-9, CPB4-9, and CPB3-9 carbons (see Figure S5), which were prepared by using 12 ACS Paragon Plus Environment

Page 13 of 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 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


smaller amount of PB, show a shoulder at 2θ= 0.90-0.95, the analysis of which allowed for assignment of d-spacing values equal to 10.2, 10.4, and 10.8 nm, respectively. However, the remaining samples studied did not exhibit the aforementioned peak or shoulder, indicating deterioration of the mesoporous structure of with increasing amount of the PB used in the synthesis, caused by Fe-catalyzed graphitization (see discussion in previous section). As shown in Figure 3C and D, the wide-angle XRD patterns of the CPB-9 and CPB*-9 carbons, respectively, exhibit several well-resolved diffraction peaks. The peaks observed at 2θ = 26, 43 and 78o can be indexed as (002), (101) and (110) reflections of graphitic carbon, respectively. The (002) diffraction peak observed at 2θ= 26 for CPB*5-6 (see Fig. S6), indicates that graphitization was initiated at ~600 oC. This observation provides further evidence that the CPB*5-6 sample was partially graphitic, which has been also confirmed by TGA estimation of its graphitization degree at 13% level. The stacking crystal thickness of graphitic domains in the sample studied was estimated between 5.4 and 7.7 nm (see Table S1). As can be seen in this table that size and percentage of graphitic domains increases with increasing amount of the PB catalyst and carbonization temperature. The values of d002 for the carbons studied are tabulated in Table S1. These values are ranging from 0.339 to 0.344 nm, and are very close to d002 spacing of graphite (i.e., 0.335nm). Further, the diffraction peaks centered at 2θ of 35.6, 43.5, 53.9, and 62.8o can be assigned as γ-Fe2O3 (see Figure S6). It should be also noted that the broad peak observed around 43-44o can be ascribed to an overlapping of strong (101) reflection (JCPDS No. 75-1621) of the graphitic carbon with (400) reflection (JCPDS No. 89-5892) of γ-Fe2O3. Moreover, a sharp peak observed at 44.7o can be assigned as (110) reflection (JCPDS No. 33-0664) of α-Fe phase. The particle sizes of γ-Fe2O3 in the composite estimated by using Debye-Scherrer’s equation from the XRD peak at 2θ = 35.6o are 30 and 21 nm for CPB4-9 and CPB*5-9, respectively; however, the particle size of α-Fe calculated by using 2θ = 44.7o is ~27nm for CPB*1-9, CPB4-9 and CPB*5-9. These particle sizes are comparable with the values obtained from the TEM images (see Figures 4, S7 and S8). Namely, the sizes of the ferric oxide particles estimated for CPB4-9, CPB*1-9 and CPB*5-9 estimated ACS Paragon Plus Environment

13


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 14 of 22

by TEM analysis were below 50 nm. The graphitic stacking thickness for the aforementioned carbons was estimated to be 4-8, 4-7, and 4-12 nm, respectively. Interestingly, the GC samples exhibited magnetic properties as shown in Figure S9. This figure shows that the water suspended CPB*5-9 sample was easily separated from the solution upon exposure to an external magnet. Thus, these magnetically separable GCs could be used for the liquid-phase adsorptionbased separations such as removal of pollutants from water.34

Figure 4. The high-resolution TEM (HRTEM) images for CPB*5-9 (a-d), CPB*1-9 (e-g) and CPB4-9 (h-i).


14

Page 15 of 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 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Transmission electron microscopy (TEM) studies. The high-resolution TEM (HRTEM) images for CPB4-9, CPB*1-9 and CPB*5-9 were obtained to study the structural properties of the carbon samples. As shown in Figure 4, both CPB4-9 and CPB*1-9 exhibited ordered mesopores with d-spacing values of 10.2 and 10.4 nm, which are in a good agreement with those obtained by the XRD analysis. However, the CPB*5-9 carbon did not possess of ordered mesostructures, which is in agreement with small-angle XRD pattern. Figure 4 further reveals that the TEM image of CPB*5-9 resembles somewhat images for onion-like graphitic structures with small voids (nanometer size) between graphitic domains. The size of these voids was estimated in micro- and meso-range, and could reach even 21 nm. These voids (pores) created during catalyzed transformation of amorphous carbon to graphitic one are the major reason of broad pore size distributions observed in Figure 1. The contrast images of CPB4-9 and CPB*5-9 (Figures S10 and S11) show that the PB-derived iron oxide particles are well dispersed through the carbon structure. This is caused by a good dispersion of the PVP-stabilized PB nanoparticles in the polymer-templated phenolic resin mesostructure due to favorable interactions between hydrophilic PVP-coated PB nanoparticles and hydrophilic ethylene oxide units of Pluronic F127 block copolymer. The hydrophilic nature of PVP-stabilized PB nanoparticles was confirmed by a simple test, involving their behavior in water (hydrophilic) and octane (hydrophobic) phases. It was shown that the PVP-coated PB nanoparticles are better dispersed in water than octane, indicating their hydrophilic nature. Thus, the PVP-stabilized PB nanoparticles can be accumulated in hydrophilic domains (ethylene oxide region) of ordered mesostructures. Similar observation was also reported by Gao et.al,28 who claimed that hydrophilic interactions between [Fe(H2O)x]3+ and EO groups resulted in a good dispersion of iron particles in the carbon structure. For the system studied, the polymeric template was decomposed during initial thermal treatment (up to ~400 oC) in nitrogen, while the PB-derived Fe- and K-containing nanoparticles were retained in phenolic resin mesostructure. At higher temperatures the Fe-catalyzed graphitization took place, which resulted in the formation of graphitic domains and deterioration of mesostructure. The potassium species trapped inside carbon structure can be removed by excessive


15


washing of the sample with water. Initially, our aim was to obtain the PB-polymer composites by using citrate- or PVP (high loading)-stabilized PB nanoparticles. However, both these experiments gave milky-colored polymeric phase and blue-colored aqueous phase, indicating that the BP particles were not incorporated into the polymeric phase. Therefore, it is essential to use an appropriate amount of PVP for the stabilization of the PB nanoparticles and their efficient incorporation into the polymeric mesophase. To investigate the composition of nanoparticles in the carbon, the energy-dispersive X-ray spectroscopy (EDX) was performed for both CPB4-9 and CPB*5-9. As shown in Figures S10 and S11, the appearance of iron peaks is a clear indication of the presence of iron-containing nanoparticles. It is noteworthy that the EDX spectrum obtained from area B without visible iron particles showed the presence of iron, which could be associated with the nanometer-sized iron particles that could be responsible for catalytic graphitization. The EDX spectra further revealed the presence of very weak potassium peaks, indicating the trace amount of potassium that was responsible for lowering the oxidation temperature of both amorphous and graphitic carbons observed in the TGA analysis. 300

400 5 10 20 50 100

200

CPB*1-9

mV/s mV/s mV/s mV/s mV/s

Specific capacitance (F/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 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 22

100

0

-100

A -0.2

0.0

0.2

0.4

0.6

0.8

5 mV/s 10 mV/s 20 mV/s 50 mV/s 100 mV/s

300

CPB4-9

200 100 0 -100

B

-200 1.0

-0.2

0.0

Potential (V) vs. SCE

0.2

0.4

0.6

0.8

1.0

Potential (V) vs. SCE

Figure 5. The CV curves for CPB*-9 (A) and CPB4-9 (B) electrodes at various scan rates ranging from 5 to 100 mVs-1.

Electrochemical studies. The cyclic voltammetry (CV) curves were obtained for CPB*1-9 and CPB4-9 (both samples possessed almost equal specific surface area) to show their performance as electrodes for supercapacitors. These curves were recorded using a three electrode cell within the potential range from 16 ACS Paragon Plus Environment

Page 17 of 22

-0.2 V to 1.0 V in 1.0 M H2SO4 electrolyte and by varying the scanning rate from 5 to 100 mVs-1 (see Figure S12). As shown in Figures 5 A and B, the CV curves obtained between -0.2 V and 1.0 V are nearly quasirectangular shaped voltammograms at all voltage sweep rates, indicating good ion and charge transportation within the electrodes studied and some pseudocapacitive behavior due to iron containing nanoparticles.37-38 The mesoporous structure and graphitic nature of the carbon studied seem to enhance the ion and current transport, respectively. An increase in the oxidation current at 0.6 V on the CV plots is a clear indication of some pseudocapacitance. Since both materials studied contained very small amounts of iron oxide species (< 4.2%, see Table S1), the overall energy storage of these mesoporous graphitic carbons is a combination of two contributions, the major one representing the double-layer capacitance and a minor Faradaic pseudocapacitance contribution due to the presence of residual iron oxide species. 200

A 200

150

100

50

CPB*1-9 CPB4-9


250


B

180

160

140 CPB4-9 CPB*1-9

120

100

0 0

20

40

60

80

0

100

20

40

60

80

100

120

140

Number of charge-discharge cycles

Scan rate (mV/s) 20000 CPB*1-9 CPB4-9

C

10

15000

Z" (Ohm)

8

Z" (Ohm)

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


10000

6 4 2

5000 0 26

28

30

32

34

Z' (Ohm)

0 0

5000

10000

15000

20000

Z' (Ohm)

Figure 6. The CV curves at different scan rates (A), cycling tests at a scan rate of 50mVs-1(B), and Nyquist plots (C) for both CPB*1-9 and CPB4-9.


17


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 18 of 22

Figure 6A recapitulates the specific capacitance for the carbon electrodes studied deduced from the CV measurements at different scan rates. The gravimetric specific capacitance of CPB*1-9 and CPB4-9 decreased from 150 and 211 Fg-1 at 5 mVs-1 to 100 and 171 Fg-1 at 100 mVs-1, respectively. These correspond to the capacitance retention of 67 % and 81 % for CPB*1-9 and CPB4-9, respectively. In spite of similar surface area of both CPB4-9 and CPB*1-9, the former sample showed very high capacitance retention. This superior capacitance retention of CPB4-9 can be attributed to the fast ion transport in the porous structure at high current loads, mainly due to the presence of large fraction of graphitic domains in the carbon (~40%) and large mesopores (7.3 nm). The observed capacitance retention (81%) for CPB4-9 is higher than the corresponding values for many carbons including activated carbons, carbon composites, nanofibers,39 hierarchical carbons and comparable with the values obtained for graphene, carbon nanotubes and graphitic carbons.33 Also, the efficiency of ion-accessible surface area, the areal capacitance, for CPB*1-9 and CPB4-9 was obtained using gravimetric capacitance and the specific surface area of the respective samples. The resulting values for CPB*1-9 and CPB4-9 are 25 and 34 µF cm-2, respectively, which are higher than the areal capacitance values reported so far for the most porous carbons, graphene, and graphitic carbons in aqueous electrolytes40,41(see Table S2). As shown in Fig. 6B, the cycle stability of CPB*1-9 and CPB4-9 was evaluated at scan rate of 50 mVs-1 up to 150 cycles. This evaluation showed that there is no any capacitance loss for both samples during 150 cycles, indicating an excellent stability of the carbons studied as electrodes for supercapacitors. The Nyquist plots of impedance are shown in Figure 6C.The straight lines in the low-frequency region are close to the real impedance axis, indicating better wettability with electrolyte and mass transportation mainly due to the porous structure composed of large mesopores. Also, the galvanostatic charge/discharge curves were recorded for the CPB*1-9 and CPB4-9 samples at a constant current density; these charge/discharge data were used to calculate the specific capacitance as shown in earlier works42,43 (see Figure S13 in supporting information). The


18

Page 19 of 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 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


resulting values at the constant current density = 0.2 A/g are equal to 168 and 209 F/g for the CPB*1-9 and CPB4-9 samples, respectively.

CONCLUSIONS This work shows that mesoporous graphitic carbons can be obtained by a simple one-pot synthesis using resorcinol and formaldehyde as carbon precursors, PVP-stabilized Prussian blue nanoparticles as a graphitization catalyst and block copolymer as a soft template under acidic conditions. Interestingly, mesoporous carbons with 13% of graphitic domains were obtained at 600 oC, which is considered to be a very low temperature for graphitization process. Note that the aforementioned 13% graphitization degree is the highest ever reported value for phenolic resin-based carbons at 600 oC. Furthermore, it was shown that mesoporous carbons with graphitic domains exceeding 80% were obtained at 700 oC. These graphitic carbons possessed relatively high specific surface area and mesoporous structure, which resulted in excellent electrochemical properties such as very high gravimetric capacity, reaching 211 and 150 Fg-1 for CPB4-9 and CPB*1-9, respectively. Moreover, CPB4-9 showed very high areal capacitance, reaching 34.1 µFcm-2 at 5 mVs-1 scan rate, which is higher than those reported for many types of porous carbons. The current study shows that the mesoporous graphitic carbons studied have potential to be used for various energy-related applications. In addition, their magnetic properties make them attractive materials for liquid phase adsorption/separation processes. Further studies are planned to improve the surface area, mesoporosity and capacitance of these carbons without worsening their graphitic structure. ASSOCIATED CONTENT Supporting information Two tables listing XRD, TEM, TG and adsorption data and 13 figures showing the TG/DTG profiles, small and wide angle XRD patterns, picture illustrating magnetic properties, STEM Z-contrast images


19


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 20 of 22

and EDX spectra, CV and galvanostatic charge/discharge curves, and TEM images of the carbons studied. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author Phone 330-672-3790; Fax 330672-672-3816; e-mail [email protected]. ACKNOWLEDGMENT The TEM data were obtained at the (cryo) TEM facility at the Liquid Crystal Institute, Kent State University, supported by the Ohio Research Scholars Program Research Cluster on Surfaces in Advanced Materials. REFERENCES (1) Wu, Z.; Li, W.; Xia, Y.; Webley, P.; Zhao, D. J. Mater. Chem. 2012, 22, 8835-8845. (2) Srinivasu, P.; Islam, A.; Singh, S. P.; Han, L.; Kantam, M. L.; Bhargava, S. K. J. Mater. Chem. 2012, 22, 20866-20869. (3) Qi, J.; Jiang, L.; Tang, Q.; Zhu, S.; Wang, S.; Yi, B.; Sun, G. Carbon 2012, 50, 2824-2831. (4) Huang, C.; Zhang, Q.; Chou, T.; Chen, C.; Su, D. S.; Doong, R. ChemSusChem 2012, 5, 563-571. (5) Dai, M.; Vogt, B. D. J. Colloid Interface Sci. 2012, 387, 127-134. (6) Wickramaratne, N. P.; Jaroniec, M. Carbon 2013, 51, 45-51. (7) He, X.; Zhou, L.; Nesterenko, E. P.; Nesterenko, P. N.; Paull, B.; Omamogho, J. O.; Glennon, J. D.; Luong, J. H. T. Anal. Chem. 2012, 84, 2351-2357. (8) Liang, C.; Xie, H.; Schwartz, V.; Howe, J.; Dai, S.; Overbury, S. H. J. Am. Chem. Soc. 2009, 131, 7735-7737. (9) Li, J.; Lu, R.; Dou, B.; Ma, C.; Hu, Q.; Liang, Y.; Wu, F.; Qiao, S.; Hao, Z. Environ. Sci. Technol. 2012, 46, 12648-12654. (10) Niu, H.; Wang, Y.; Zhang, X.; Meng, Z.; Cai, Y. ACS Appl. Mater. Interfaces 2012, 4, 286-295. (11) Fulvio, P. F.; Mayes, R. T.; Wang, X.; Mahurin, S. M.; Bauer, J. C.; Presser, V.; McDonough, J.; Gogotsi, Y.; Dai, S. Advanced Functional Materials 2011, 21, 2208-2215. (12) Wickramaratne, N. P.; Jaroniec, M. J. Mater. Chem. A 2013, 1, 112-116. (13) Wickramaratne, N. P; Jaroniec, M. ACS Appl. Mater. Interfaces 2013, 5,1849-1855.


20

Page 21 of 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 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(14) Wickramaratne, N.; Jaroniec, M. RSC Adv. 2012, 2, 1877-1883. (15) You, B.; Zhang, Z.; Zhang, L.; Yang, J.; Zhu, X.; Su, Q. RSC Adv. 2012, 2, 5071-5074. (16) Chmiola, J.; Yushin, G.; Gogotsi, Y.; Portet, C.; Simon, P.; Taberna, P. L. Science 2006, 313, 1760-1763. (17) Simon, P. F.; Gogotsi, Y. Phil. Trans. R. Soc. A 2010, 368, 3457–3467 (18) Pandolfo, A. G.; Hollenkamp, A. F. J. Power Sources 2006, 157, 11-27. (19) Vazquez-Santos, M. B.; Geissler, E.; Laszlo, K.; Rouzaud, J.; Martinez-Alonso, A.; Tascon, J. M. D. Carbon 2012, 50, 2929-2940. (20) Patel, M. N.; Wang, X.; Slanac, D. A.; Ferrer, D. A.; Dai, S.; Johnston, K. P.; Stevenson, K. J. J. Mater. Chem. 2012, 22, 3160-3169. (21) Yoon, S. B.; Chai, G. S.; Kang, S. K.; Yu, J.; Gierszal, K. P.; Jaroniec, M. J. Am. Chem. Soc. 2005, 127, 4188-4189. (22) Su, P.; Jiang, L.; Zhao, J.; Yan, J.; Li, C.; Yang, Q. Chem. Commun. 2012, 48, 8769-8771. (23) Lu, A.; Li, W.; Salabas, E.; Spliethoff, B.; Schuth, F. Chem. Mater. 2006, 18, 2086-2094. (24) Chen, Z.; Weng, D.; Sohn, H.; Cai, M.; Lu, Y. RSC Adv. 2012, 2, 1755-1758. (25) Yuan, D.; Yuan, X.; Zou, W.; Zeng, F.; Huang, X.; Zhou, S. J. Mater. Chem. 2012, 22, 1782017826. (26) Wang, Y.; Li, B.; Zhang, C.; Song, X.; Tao, H.; Kang, S.; Li, X. Carbon 2013, 51, 397-403. (27) Wang, A.; Ren, J.; Shi, B.; Lu, G.; Wang, Y. Microporous and Mesoporous Materials 2012, 151, 287-292. (28) Gao, W.; Wan, Y.; Dou, Y.; Zhao, D. Adv. Energy Mater. 2011, 1, 115-123. (29) Li, J.; Fiset, E.; Yang, J.; Yuan, P.; Ling, X.; Hulicova-Jurcakova, D.; Yu, C.; Wang, L. J. Mater. Chem. 2012, 22, 21472-21480. (30) Brunauer, S.; Emmett, P. H.; Teller, E. J. Am. Chem. Soc. 1938, 60, 309-319. (31) Kruk, M.; Jaroniec, M. Chem. Mater. 2001, 13, 3169-3183. (32) Yao, J.; Li, L.; Song, H.; Liu, C.; Chen, X. Carbon 2009, 47, 436-444. (33) Wang, D.; Li, F.; Liu, M.; Lu, G.; Cheng, H. Angew. Chem., Int. Ed. 2008, 47, 373-376. (34) Huang, C.; Doong, R.; Gu, D.; Zhao, D. Carbon 2011, 49, 3055-3064. (35) Kiciński, W.; Norek, M.; Bystrzejewski, M. Journal of Physics and Chemistry of Solids 2013, 74, 101-109. (36) Ogura, M.; Morozumi, K.; Elangovan, S. P.; Tanada, H.; Ando, H.; Okubo, T. Applied Catalysis B, Environmental 2008, 77, 294-299. (37) Sassin, M. B.; Mansour, A. N.; Pettigrew, K. A.; Rolison, D. R.; Long, J. W. ACS Nano 2010, 4, 4505-4514. ACS Paragon Plus Environment

21


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 22

(38) Zhao, X.; Johnston, C.; Grant, P. S. J. Mater. Chem. 2009, 19, 8755-8760. (39) Wang, K.; Wang, Y.; Wang, Y.; Hosono, E.; Zhou, H. J. Phys. Chem. C 2009, 113, 1093-1097. (40) Wu, Z.; Sun, Y.; Tan, Y.; Yang, S.; Feng, X.; Mullen, K. J. Am. Chem. Soc. 2012, 134, 1953219535. (41) Zhong, M.; Kim, E. K.; McGann, J. P.; Chun, S.; Whitacre, J. F.; Jaroniec, M.; Matyjaszewski, K.; Kowalewski, T. J. Am. Chem. Soc. 2012, 134, 14846-14857. (42) Stoller, M.D.; Park, A.; Zhu, Y.; An, J.; Ruoff, R.S. Nano Lett. 2008, 8 , 3498-3502. (43) Lu, T.; Zhang, Y.; Li, H.; Pan, L.; Li, Y.; Sun, Z. Electrochimica Acta 2010, 55, 4170-4173.


22

Graphitic Mesoporous Carbons with Embedded Prussian Blue

Recommend Documents