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Structure and supercapacitive performance of hierarchical porous carbon obtained by catalyzing microporous carbide-derived carbon
Materials Letters 139 (2015) 340–343
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Structure and supercapacitive performance of hierarchical porous carbon obtained by catalyzing microporous carbide-derived carbon Pengtao Yan a, Jiang Xu a, Chao Wu a,b, Ruijun Zhang a,n, Jianglong Jin a a b
State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China Hebei United University, Tangshan 063009, China
art ic l e i nf o
a b s t r a c t
Article history: Received 27 June 2014 Accepted 11 October 2014 Available online 23 October 2014
Microporous carbide-derived carbon (CDC) with both high SSA and extremely narrow pore size distribution is synthesized by chlorination of niobium carbide powder. The produced microporous CDC is catalyzed at 1000 1C by using nickel nitrate as the catalyst. This treatment leads to the formation of a small amount of mesopores and slight decrease in the SSA. Electrochemical investigations show that the specific capacitance of the CDC catalyzed by nickel nitrate is almost as high as that of the pristine CDC in 6M KOH electrolyte. Furthermore, its cyclic voltammogram curves can keep a rectangular-like shape even at a scan rate of 500 mV s 1, a significant improvement compared with that of the pristine CDC, indicating that the catalyzed CDC as an electrode material for supercapacitor exhibits superior specific capacitance and rate performance. Therefore, catalyzing CDC may be regarded as a facile and effective strategy to tune the CDC pore structure to match the applications of supercapacitor or some others. & 2014 Elsevier B.V. All rights reserved.
Keywords: Carbon materials Porous materials Catalysis Supercapacitive performance
1. Introduction Carbide-derived carbon (CDC) is a type of carbon produced by selective removal the metal or metalloid atoms from carbides [1]. It shows several outstanding advantages over traditional carbon materials, such as high specific surface area (SSA) and tunable pore size with a narrow distribution [2]. Because of the unique microstructure, the CDC exhibits potential application in the fields of electric double-layer capacitors (EDLCs) [3,4], hydrogen and methane storage [5], catalyst supports [6] and so on. It has been recognized that the CDC structure can be influenced by the catalyst incorporated during the CDC formation process. Kormann et al. [7] found that the introduction of transition metal catalysts during chlorination led to the increase of the degree of graphitization. Some other carbon structures (e.g. carbon onions [8], barrel-like carbon [9]) can also be formed due to the effect of catalyst. Besides, Käärik et al. [10] and Xu et al. [11] reported that, during the chlorination, the presence of catalyst caused the formation of a large amount of mesopores and consequently a great decrease in SSA. However, up to now, few work concerns the effect of catalyst on the produced CDC. In this work, we investigated the structural evolution of a microporous CDC due to the introduction of nickel nitrate as
n
Corresponding author. Tel.: þ 86 335 8387598. E-mail address: [email protected] (R. Zhang).
http://dx.doi.org/10.1016/j.matlet.2014.10.063 0167-577X/& 2014 Elsevier B.V. All rights reserved.
catalyst and the effect of incorporated catalyst on the pore characteristics and electrochemical properties of the CDC.
2. Experimental 2.1. Sample preparation The NbC powder (99.5%, 2 mm, Changsha Xinlan Cemented Carbide Co. Ltd, P.R. China) was placed in a horizontal quartz tube furnace and heated to 800 1C under argon at atmospheric pressure. The argon flow was stopped when the temperature reached 800 1C, and the pure chlorine was passed through the quartz tube at a flow rate of 20 ml min 1. The chlorination lasted for 2.5 h. The produced chloride gas was blown away by the chlorine flow immediately during the chlorination. At last, the quartz tube was purged with argon for 10 min at a rate of 1.5 L min 1 and cooled down to room temperature. The waste chlorine and chloride gas were adsorbed by 1 M NaOH solution. The produced CDC (denoted as NbC-CDC) and nickel nitrate (1:0.3 in weight) were added in ethanol, thoroughly mixed by ultrasonic stirring for 10 min, and dried in an oven at 50 1C overnight. Thereafter, the dried mixture was placed in a horizontal quartz tube furnace and heated to 1000 1C at a rate of 15 1C min 1 under argon at atmospheric pressure. The treatment lasted for 4 h and cooled down to room temperature at argon atmosphere. The catalyzed sample (denoted as NbC-CDC/Ni) was washed by
P. Yan et al. / Materials Letters 139 (2015) 340–343
hydrochloric acid and then deionized water to pH ¼7 to ensure the sufficient removal of residual metals. 2.2. Characterization The microstructure of the samples was observed using a JEM2010 transmission electron microscopy (TEM) at 200 kV. X-ray
341
diffraction (XRD) patterns between 10 (2θ) and 70 (2θ) degrees were collected using Rigaku D/MAX-2500 powder diffractometer with Cu-Kα radiation (λ ¼0.154 nm) operated at 40 kV and 200 mA. Gas adsorption/desorption analysis was done in the VSorb 2800TP surface area and pore distribution analyzer (Gold APP Instruments Corporation, China) with N2 as adsorbent at 77 K. Prior to analysis, samples were degassed in vacuum at 200 oC for
Fig. 1. The HRTEM images (a, b) and XRD patterns (c, d) of both NbC-CDC and NbC-CDC/Ni.
Fig. 2. Low-temperature N2 adsorption/desorption isotherms (a) and pore size distributions (b) of both NbC-CDC and NbC-CDC/Ni. The inset in (b) is the mesopore size distribution.
342
P. Yan et al. / Materials Letters 139 (2015) 340–343
8 h. The SSA, according to BET (Brunauer, Emmet and Teller) theory and nanopore volume, was calculated by using t-plots based on the N2 sorption isotherm. Pore size distributions were calculated using the Horvath–Kawazoe method and assuming a slit-pore model. 2.3. Preparation of electrode and electrochemical measurement The electrochemical investigations were carried out in a threeelectrode system using platinum as counter electrode and Hg/HgO as a reference electrode. The working electrodes were prepared as follows: A slurry consisting of 80 wt.% CDC, 10 wt.% carbon black and 10 wt.% polytetrafluoroethylene (PTFE, 60 wt.% suspension in water) binder was smeared into nickel foam and dried in vacuum at 120 1C for 10 h. Thereafter, the electrode was pressed at a pressure of 10 MPa. A 6 M KOH solution was used as electrolyte. The active area of the electrode is 1 cm2. Before each measurement, the working electrode was impregnated with electrolyte to ensure thoroughly wetted by electrolyte. Cyclic voltammograms (CVs) were collected on CHI650D electrochemical workstation in a potential range of 0.9 0.1 V. The scan speeds for all CV tests were in the range of 5 500 mV s 1.
3. Results and discussion TEM is an effective technology that can be used to reveal the microstructure of materials at the atomic scale. Fig. 1 shows the high-resolution TEM (HRTEM) of NbC-CDC and NbC-CDC/Ni. It can be seen that the NbC-CDC is composed of a large amount of disordered graphite flakes, which contribute the micropores (the slit-pore among these flakes, Fig. 1a). For the NbC-CDC/Ni, shown in Fig. 1b, the structure observed near the catalyst (elliptical marker) is mainly composed of highly curved graphenes, where the degree of order of the CDC is a little higher than other parts. Furthermore, some larger pores (4 2 nm, mesopore) can be detected among these highly curved graphenes. The scanning Table 1 Porosity characteristics of NbC-CDC and NbC-CDC/Ni. Sample
SBET (m2 g 1)
Vmicro (cm3 g-1)
Vmeso (cm3 g 1)
Average micropore size (nm)
Average micropore size (nm)
NbC-CDC NbC-CDC/Ni
2029 1822
0.82 0.73
0.11 0.38
0.86 0.85
3.8
electron microscopy observations of the samples NbC-CDC and NbC-CDC/Ni exhibit no obvious change in morphology (Figure S1, supporting information), indicating that the nickel nitrate as catalyst has no significant effect on the CDC morphology.Therefore, it can be concluded that catalysis can change the microstructure and consequently the pore structure of the CDC. XRD patterns of the two produced CDC samples are shown in Fig. 1c and d. A slight obvious peak at 26 1 (2θ) in the pattern of NbC-CDC/Ni (Fig. 1d) may suggest more graphite structures with interlayer spacing of 0.34 nm. The weak peaks at 2θ ¼ 37 1 and 63 1, corresponding to the peaks of NiO (refer to PDF no. 47– 1049), are observed in the XRD pattern (Fig. 1d). Thermal gravimetric analysis shows that only trace of residual NiO (nearly cannot be detected) exists in NbC-CDC/Ni. To probe into the effect of catalyst on the CDC pore structure, the low-temperature N2 adsorption/desorption isotherms and pore size distributions of NbC-CDC and NbC-CDC/Ni are shown in Fig. 2. It can be observed from Fig. 2a that both NbC-CDC and NbC-CDC/Ni adsorb N2 at low pressure (P/P0) largely, indicating the microporous property of these two samples. In addition, a notable hysteresis loop is observed in the adsorption/desorption isotherm of NbC-CDC/Ni, suggesting the existence of mesopores. From the inset of Fig. 2b, it can be estimated that the mesopore size distribution is 3.8 nm. To further investigate the pore properties, more detailed porosity characteristics of NbC-CDC and NbCCDC/Ni are listed in Table 1. The SSA of NbC-CDC and NbC-CDC/Ni are 2029 m2 g 1 and 1822 m2 g 1, respectively. Obviously, the decrease in the SSA of NbC-CDC/Ni should be attributed to the formation of mesopores caused by the catalyst. As the catalyzing only leads to the formation of a small amount of mesopores and the structural evolution in the neighboring CDC regions, and therefore, most of the pristine CDC structure can be maintained, there occurs no significant change between the average micropore size of NbC-CDC (0.86 nm) and NbC-CDC/Ni (0.85 nm). The CVs of the CDCs with and without catalyzing are measured and shown in Fig. 3, aiming to disclose the effect of catalysis on the electrochemical properties. It can be seen that both NbC-CDC/Ni and NbC-CDC show a comparable specific capacitance. But, the rate performance for the NbC-CDC/Ni exhibits a significant improvement compared with that for the NbC-CDC, which can be identified by the rectangular-like shape CV curves of NbC-CDC/Ni even at a scan rate of 500 mV s 1. For the EDLCs, micro/mesoporous carbon structure has been widely accepted to be beneficial for the achievement of good electrochemical properties, as the micropores are useful for accumulation of charges to obtain high capacitance, and the mesopores can provide favorable channels for electrolyte fast transport to acquire good rate performance. As mentioned above,
Fig. 3. Cyclic voltammograms of NbC-CDC (a) and NbC-CDC/Ni (b) at different scan rates.
P. Yan et al. / Materials Letters 139 (2015) 340–343
the NbC-CDC and the NbC-CDC/Ni have a comparable specific volume of micropores, thereby showing no obvious difference in the specific capacitance. However, the specific volume of mesopores for the NbC-CDC/Ni is almost three times higher than that for the NbC-CDC, which undoubtedly contributes to the significant improvement in rate performance. Therefore, catalyzing microporous CDC is an effective method to achieve good rate performance and keep high specific capacitance.
343
Acknowledgment Financial support of this work by National Science Foundation of China (NSFC) (No. 50975247) and Hebei Natural Science Foundation (No. E2014203204) is acknowledged. Appendix A. Supporting information Supplementary material related to this article can be found online at http://dx.doi.org/10.1016/j.matlet.2014.10.063.
4. Conclusions In this article, microporous NbC-CDC with high SSA and extremely narrow pore size distribution is catalyzed with nickel nitrate. This treatment results in the formation of highly curved graphenes near the catalyst, which contributes a small amount of mesopores. Compared with the pristine NbC-CDC, the catalyzed NbC-CDC exhibits slightly lower specific volume of micropores but much higher specific volume of mesopores. There is no significant difference in the specific capacitance between the pristine NbCCDC and the catalyzed NbC-CDC. However, an obvious improvement in the rate performance for the catalyzed NbC-CDC has been achieved by comparison to that for the pristine NbC-CDC. Therefore, catalyzing CDC can be used as an effective method to tune the pore structure to improve the capacitor characteristics or match other different applications.
References [1] Gogotsi Y, Yoshimura M. Nature 1994;367:628–30. [2] Gogotsi Y, Nikitin A, Ye H, Zhou W, Fischer JE, Yi B, et al. Nature Materials 2003;2:591–4. [3] Simon P, Gogotsi Y. Nature Materials 2008;7:845–54. [4] Xu J, Zhang R, Wu C, Zhao Y, Ye X, Ge S. Carbon 2014;74:226–36. [5] Dash R, Chmiola J, Yushin G, Gogotsi Y, Laudisio G, Singer J, et al. Carbon 2006;44:2489–97. [6] Ersoy DA, McNallan MJ, Gogotsi Y. Journal of The Electrochemical Society 2001;148:C774–9. [7] Kormann M, Gerhard H, Zollfrank C, Scheel H, Popovska N. Carbon 2009;47:2344–51. [8] Xu J, Zhang R, Wang J, Ge S, Wen F. Materials Letters 2012;88:168–70. [9] Perkson A, Leis J, Arulepp M, Käärik M, Urbonaite S, Svensson G. Carbon 2003;41:1729–35. [10] Käärik M, Arulepp M, Karelson M, Leis J. Carbon 2008;46:1579–87. [11] Xu J, Zhang R, Ge S, Wang J, Liu Y, Chen P. Materials Chemistry and Physics 2013;141:540–8.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Structure and supercapacitive performance of hierarchical porous carbon obtained by catalyzing microporous carbide-derived carbon Pengtao Yan a, Jiang Xu a, Chao Wu a,b, Ruijun Zhang a,n, Jianglong Jin a a b
State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China Hebei United University, Tangshan 063009, China
art ic l e i nf o
a b s t r a c t
Article history: Received 27 June 2014 Accepted 11 October 2014 Available online 23 October 2014
Microporous carbide-derived carbon (CDC) with both high SSA and extremely narrow pore size distribution is synthesized by chlorination of niobium carbide powder. The produced microporous CDC is catalyzed at 1000 1C by using nickel nitrate as the catalyst. This treatment leads to the formation of a small amount of mesopores and slight decrease in the SSA. Electrochemical investigations show that the specific capacitance of the CDC catalyzed by nickel nitrate is almost as high as that of the pristine CDC in 6M KOH electrolyte. Furthermore, its cyclic voltammogram curves can keep a rectangular-like shape even at a scan rate of 500 mV s 1, a significant improvement compared with that of the pristine CDC, indicating that the catalyzed CDC as an electrode material for supercapacitor exhibits superior specific capacitance and rate performance. Therefore, catalyzing CDC may be regarded as a facile and effective strategy to tune the CDC pore structure to match the applications of supercapacitor or some others. & 2014 Elsevier B.V. All rights reserved.
Keywords: Carbon materials Porous materials Catalysis Supercapacitive performance
1. Introduction Carbide-derived carbon (CDC) is a type of carbon produced by selective removal the metal or metalloid atoms from carbides [1]. It shows several outstanding advantages over traditional carbon materials, such as high specific surface area (SSA) and tunable pore size with a narrow distribution [2]. Because of the unique microstructure, the CDC exhibits potential application in the fields of electric double-layer capacitors (EDLCs) [3,4], hydrogen and methane storage [5], catalyst supports [6] and so on. It has been recognized that the CDC structure can be influenced by the catalyst incorporated during the CDC formation process. Kormann et al. [7] found that the introduction of transition metal catalysts during chlorination led to the increase of the degree of graphitization. Some other carbon structures (e.g. carbon onions [8], barrel-like carbon [9]) can also be formed due to the effect of catalyst. Besides, Käärik et al. [10] and Xu et al. [11] reported that, during the chlorination, the presence of catalyst caused the formation of a large amount of mesopores and consequently a great decrease in SSA. However, up to now, few work concerns the effect of catalyst on the produced CDC. In this work, we investigated the structural evolution of a microporous CDC due to the introduction of nickel nitrate as
n
Corresponding author. Tel.: þ 86 335 8387598. E-mail address: [email protected] (R. Zhang).
http://dx.doi.org/10.1016/j.matlet.2014.10.063 0167-577X/& 2014 Elsevier B.V. All rights reserved.
catalyst and the effect of incorporated catalyst on the pore characteristics and electrochemical properties of the CDC.
2. Experimental 2.1. Sample preparation The NbC powder (99.5%, 2 mm, Changsha Xinlan Cemented Carbide Co. Ltd, P.R. China) was placed in a horizontal quartz tube furnace and heated to 800 1C under argon at atmospheric pressure. The argon flow was stopped when the temperature reached 800 1C, and the pure chlorine was passed through the quartz tube at a flow rate of 20 ml min 1. The chlorination lasted for 2.5 h. The produced chloride gas was blown away by the chlorine flow immediately during the chlorination. At last, the quartz tube was purged with argon for 10 min at a rate of 1.5 L min 1 and cooled down to room temperature. The waste chlorine and chloride gas were adsorbed by 1 M NaOH solution. The produced CDC (denoted as NbC-CDC) and nickel nitrate (1:0.3 in weight) were added in ethanol, thoroughly mixed by ultrasonic stirring for 10 min, and dried in an oven at 50 1C overnight. Thereafter, the dried mixture was placed in a horizontal quartz tube furnace and heated to 1000 1C at a rate of 15 1C min 1 under argon at atmospheric pressure. The treatment lasted for 4 h and cooled down to room temperature at argon atmosphere. The catalyzed sample (denoted as NbC-CDC/Ni) was washed by
P. Yan et al. / Materials Letters 139 (2015) 340–343
hydrochloric acid and then deionized water to pH ¼7 to ensure the sufficient removal of residual metals. 2.2. Characterization The microstructure of the samples was observed using a JEM2010 transmission electron microscopy (TEM) at 200 kV. X-ray
341
diffraction (XRD) patterns between 10 (2θ) and 70 (2θ) degrees were collected using Rigaku D/MAX-2500 powder diffractometer with Cu-Kα radiation (λ ¼0.154 nm) operated at 40 kV and 200 mA. Gas adsorption/desorption analysis was done in the VSorb 2800TP surface area and pore distribution analyzer (Gold APP Instruments Corporation, China) with N2 as adsorbent at 77 K. Prior to analysis, samples were degassed in vacuum at 200 oC for
Fig. 1. The HRTEM images (a, b) and XRD patterns (c, d) of both NbC-CDC and NbC-CDC/Ni.
Fig. 2. Low-temperature N2 adsorption/desorption isotherms (a) and pore size distributions (b) of both NbC-CDC and NbC-CDC/Ni. The inset in (b) is the mesopore size distribution.
342
P. Yan et al. / Materials Letters 139 (2015) 340–343
8 h. The SSA, according to BET (Brunauer, Emmet and Teller) theory and nanopore volume, was calculated by using t-plots based on the N2 sorption isotherm. Pore size distributions were calculated using the Horvath–Kawazoe method and assuming a slit-pore model. 2.3. Preparation of electrode and electrochemical measurement The electrochemical investigations were carried out in a threeelectrode system using platinum as counter electrode and Hg/HgO as a reference electrode. The working electrodes were prepared as follows: A slurry consisting of 80 wt.% CDC, 10 wt.% carbon black and 10 wt.% polytetrafluoroethylene (PTFE, 60 wt.% suspension in water) binder was smeared into nickel foam and dried in vacuum at 120 1C for 10 h. Thereafter, the electrode was pressed at a pressure of 10 MPa. A 6 M KOH solution was used as electrolyte. The active area of the electrode is 1 cm2. Before each measurement, the working electrode was impregnated with electrolyte to ensure thoroughly wetted by electrolyte. Cyclic voltammograms (CVs) were collected on CHI650D electrochemical workstation in a potential range of 0.9 0.1 V. The scan speeds for all CV tests were in the range of 5 500 mV s 1.
3. Results and discussion TEM is an effective technology that can be used to reveal the microstructure of materials at the atomic scale. Fig. 1 shows the high-resolution TEM (HRTEM) of NbC-CDC and NbC-CDC/Ni. It can be seen that the NbC-CDC is composed of a large amount of disordered graphite flakes, which contribute the micropores (the slit-pore among these flakes, Fig. 1a). For the NbC-CDC/Ni, shown in Fig. 1b, the structure observed near the catalyst (elliptical marker) is mainly composed of highly curved graphenes, where the degree of order of the CDC is a little higher than other parts. Furthermore, some larger pores (4 2 nm, mesopore) can be detected among these highly curved graphenes. The scanning Table 1 Porosity characteristics of NbC-CDC and NbC-CDC/Ni. Sample
SBET (m2 g 1)
Vmicro (cm3 g-1)
Vmeso (cm3 g 1)
Average micropore size (nm)
Average micropore size (nm)
NbC-CDC NbC-CDC/Ni
2029 1822
0.82 0.73
0.11 0.38
0.86 0.85
3.8
electron microscopy observations of the samples NbC-CDC and NbC-CDC/Ni exhibit no obvious change in morphology (Figure S1, supporting information), indicating that the nickel nitrate as catalyst has no significant effect on the CDC morphology.Therefore, it can be concluded that catalysis can change the microstructure and consequently the pore structure of the CDC. XRD patterns of the two produced CDC samples are shown in Fig. 1c and d. A slight obvious peak at 26 1 (2θ) in the pattern of NbC-CDC/Ni (Fig. 1d) may suggest more graphite structures with interlayer spacing of 0.34 nm. The weak peaks at 2θ ¼ 37 1 and 63 1, corresponding to the peaks of NiO (refer to PDF no. 47– 1049), are observed in the XRD pattern (Fig. 1d). Thermal gravimetric analysis shows that only trace of residual NiO (nearly cannot be detected) exists in NbC-CDC/Ni. To probe into the effect of catalyst on the CDC pore structure, the low-temperature N2 adsorption/desorption isotherms and pore size distributions of NbC-CDC and NbC-CDC/Ni are shown in Fig. 2. It can be observed from Fig. 2a that both NbC-CDC and NbC-CDC/Ni adsorb N2 at low pressure (P/P0) largely, indicating the microporous property of these two samples. In addition, a notable hysteresis loop is observed in the adsorption/desorption isotherm of NbC-CDC/Ni, suggesting the existence of mesopores. From the inset of Fig. 2b, it can be estimated that the mesopore size distribution is 3.8 nm. To further investigate the pore properties, more detailed porosity characteristics of NbC-CDC and NbCCDC/Ni are listed in Table 1. The SSA of NbC-CDC and NbC-CDC/Ni are 2029 m2 g 1 and 1822 m2 g 1, respectively. Obviously, the decrease in the SSA of NbC-CDC/Ni should be attributed to the formation of mesopores caused by the catalyst. As the catalyzing only leads to the formation of a small amount of mesopores and the structural evolution in the neighboring CDC regions, and therefore, most of the pristine CDC structure can be maintained, there occurs no significant change between the average micropore size of NbC-CDC (0.86 nm) and NbC-CDC/Ni (0.85 nm). The CVs of the CDCs with and without catalyzing are measured and shown in Fig. 3, aiming to disclose the effect of catalysis on the electrochemical properties. It can be seen that both NbC-CDC/Ni and NbC-CDC show a comparable specific capacitance. But, the rate performance for the NbC-CDC/Ni exhibits a significant improvement compared with that for the NbC-CDC, which can be identified by the rectangular-like shape CV curves of NbC-CDC/Ni even at a scan rate of 500 mV s 1. For the EDLCs, micro/mesoporous carbon structure has been widely accepted to be beneficial for the achievement of good electrochemical properties, as the micropores are useful for accumulation of charges to obtain high capacitance, and the mesopores can provide favorable channels for electrolyte fast transport to acquire good rate performance. As mentioned above,
Fig. 3. Cyclic voltammograms of NbC-CDC (a) and NbC-CDC/Ni (b) at different scan rates.
P. Yan et al. / Materials Letters 139 (2015) 340–343
the NbC-CDC and the NbC-CDC/Ni have a comparable specific volume of micropores, thereby showing no obvious difference in the specific capacitance. However, the specific volume of mesopores for the NbC-CDC/Ni is almost three times higher than that for the NbC-CDC, which undoubtedly contributes to the significant improvement in rate performance. Therefore, catalyzing microporous CDC is an effective method to achieve good rate performance and keep high specific capacitance.
343
Acknowledgment Financial support of this work by National Science Foundation of China (NSFC) (No. 50975247) and Hebei Natural Science Foundation (No. E2014203204) is acknowledged. Appendix A. Supporting information Supplementary material related to this article can be found online at http://dx.doi.org/10.1016/j.matlet.2014.10.063.
4. Conclusions In this article, microporous NbC-CDC with high SSA and extremely narrow pore size distribution is catalyzed with nickel nitrate. This treatment results in the formation of highly curved graphenes near the catalyst, which contributes a small amount of mesopores. Compared with the pristine NbC-CDC, the catalyzed NbC-CDC exhibits slightly lower specific volume of micropores but much higher specific volume of mesopores. There is no significant difference in the specific capacitance between the pristine NbCCDC and the catalyzed NbC-CDC. However, an obvious improvement in the rate performance for the catalyzed NbC-CDC has been achieved by comparison to that for the pristine NbC-CDC. Therefore, catalyzing CDC can be used as an effective method to tune the pore structure to improve the capacitor characteristics or match other different applications.
References [1] Gogotsi Y, Yoshimura M. Nature 1994;367:628–30. [2] Gogotsi Y, Nikitin A, Ye H, Zhou W, Fischer JE, Yi B, et al. Nature Materials 2003;2:591–4. [3] Simon P, Gogotsi Y. Nature Materials 2008;7:845–54. [4] Xu J, Zhang R, Wu C, Zhao Y, Ye X, Ge S. Carbon 2014;74:226–36. [5] Dash R, Chmiola J, Yushin G, Gogotsi Y, Laudisio G, Singer J, et al. Carbon 2006;44:2489–97. [6] Ersoy DA, McNallan MJ, Gogotsi Y. Journal of The Electrochemical Society 2001;148:C774–9. [7] Kormann M, Gerhard H, Zollfrank C, Scheel H, Popovska N. Carbon 2009;47:2344–51. [8] Xu J, Zhang R, Wang J, Ge S, Wen F. Materials Letters 2012;88:168–70. [9] Perkson A, Leis J, Arulepp M, Käärik M, Urbonaite S, Svensson G. Carbon 2003;41:1729–35. [10] Käärik M, Arulepp M, Karelson M, Leis J. Carbon 2008;46:1579–87. [11] Xu J, Zhang R, Ge S, Wang J, Liu Y, Chen P. Materials Chemistry and Physics 2013;141:540–8.