A Facile Strategy to Low-Cost Synthesis of Hierarchically Porous

Research Article Cite This: ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

www.acsami.org

Facile Strategy to Low-Cost Synthesis of Hierarchically Porous, Active Carbon of High Graphitization for Energy Storage Xiang Deng,† Wenxiang Shi,† Yijun Zhong,§ Wei Zhou,† Meilin Liu,*,‡ and Zongping Shao*,§,† †

Downloaded via UNIV OF CALIFORNIA SANTA BARBARA on June 23, 2018 at 10:19:01 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemical Engineering, Nanjing Tech University, Nanjing 210009, China ‡ School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245, United States § Department of Chemical Engineering, Curtin University, Perth, WA 6845, Australia S Supporting Information *

ABSTRACT: To achieve high energy/power output, long serving life, and low cost of carbon-based electrodes for energy storage, we have developed a unique synthesis method for the fabrication of hierarchically porous carbon of high graphitization (HPCHG), derived from pyrolysis of an iron-containing organometallic precursor in a molten ZnCl2 media at relatively low temperatures. The as-prepared HPCHG has a large specific surface area (>1200 m2 g−1), abundant micro/mesopores, and plenty of surface defects. When tested in a supercapacitor (SC), the HPCHG electrode delivers 248 F g−1 at 0.5 A g−1 and a high capacitance retention of 52.4% (130 F g−1) at 50 A g−1. When tested in a sodium-ion battery (SIB), the HPCHG electrode exhibits a reversible capacity of 322 mA h g−1 at 100 mA g−1 while maintaining ∼75% of the initial stable capacity after 2000 cycles with the applied current density as high as 5000 mA g−1, implying that the HPCHG electrode is very promising for energy storage. KEYWORDS: carbon, graphitization, electrode, supercapacitor, sodium-ion battery

■

highly promising for SIBs.13 When carbon is used as an anode for an electrochemical double-layer capacitor (EDLC), high specific surface area is required since energy storage is realized through surface ion adsorption. Therefore, activated carbon with high specific surface area (SSA) is typically used as the electrode in SCs.14−16 Under optimal conditions, a volumetric capacitance of ∼60 F cm−3 and a gravimetric capacitance of ∼200 F g−1 have been reported for activated carbon materials.17 A significant challenge for the development of activated carbon materials for SCs is that an increase in the SSA is usually accompanied by a decrease in graphitization, resulting in poorer conductivity and thus lower rate capability. On the other hand, Na+ (0.95 Å) has a larger cation size compared with Li+ (0.68 Å), and if the classic intercalation−detercalation mechanism is applied on the electrode, theoretical calculation shows the average interlayer spacing in carbon should be larger than 0.37 nm, allowing easy intercalation of Na+ for energy storage.18,19 A complicated synthesis process is needed to create such expanded hard carbon materials, which could be expensive and energy intensive. In addition, due to the large cation size of Na+, the diffusion of Na+ in carbon interlayers is difficult, resulting in poor cycling rates.13,20,21 Therefore, the researchers are intensively focusing on the development of novel electrode materials with new Na+ storage mechanisms.

INTRODUCTION The rapid development of personal electronic devices, hybrid/ pure electric vehicles, as well as renewable energy utilization has stimulated a large demand for advanced energy storage systems which have the features of low cost, good safety, long life, high energy, and/or power density. To date, several types of electrochemical devices have been extensively investigated, including lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and supercapacitors (SCs).1−4 In particular, SIBs have attracted much attention in the past few years5−7 and are considered an ideal alternative to LIBs for large-scale, stationary energy storage.8 On the other hand, SCs are considered to be an important part in clean energy technologies because they fill the gap in energy and power density between conventional capacitors and batteries. The combination of SCs and SIBs may provide an ideal solution to the energy storage for smart grids that allows the direct input of intermittent renewable energies, which significantly contribute toward a sustainable future.5,9,10 Electrodes are the key components of these electrochemical storage devices and largely determine their performance. Thus, broad commercialization of SIBs and SCs requires the successful development of high-performance electrode materials with low cost. Typically, carbon plays a critical role in electrochemical energy storage devices due to its abundance, low cost, as well as good stability. Actually, graphite represents the most widely used anode materials in commercial LIBs,11 and activated carbon is the main electrode material in commercial SCs.12 Additionally, hard carbon is found to be © XXXX American Chemical Society

Received: March 23, 2018 Accepted: June 4, 2018 Published: June 4, 2018 A

DOI: 10.1021/acsami.8b04733 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces

Figure 1. Schematic illustration of the preparation method for the hierarchically porous carbon of high graphitization.

Figure 2. (a−c) Field-emission scanning electron microscopy (FE-SEM) image of the HPCHG sample with different magnifications. (d, e) Transmission electron microscopy (TEM) image and (f) nitrogen adsorption−desorption isotherm plots of the HPCHG sample. The inset is the related BJH pore size distribution (PSD) plot.

battery application, a capacitance as high as 322 mAh g−1 was attained at 0.1 A g−1, suggesting that it is a very promising carbon-based electrode for SIBs. In addition, a reversible capacity of 101 mAh g−1 was retained after 2000 cycles at 5 A g−1, which is among the highest reports for carbon electrodes in SIBs.

The facile synthesis of nanostructured carbon materials with well-tailored properties is the key to their practical use in both SCs and SIBs. Furthermore, a new energy storage mechanism is important to overcome the poor rate capability of intercalationtype hard carbon in SIBs. In addition to the intercalation of Na+ in the expanded interlayers of graphitic domains in carbon, it was reported that Na+ can also be stored by absorption at surface defects, edges, and nanovoids and by reaction with surface groups attached to carbon, thus creating capacitive charge storage (CCS).22−24 Such a CCS mechanism may provide a new alternative method to overcome the problems associated with low sodium-ion diffusion and serious structural damage during the Na+ intercalation/deintercalation cycles. Herein, we report a facile strategy to low-cost synthesis of hierarchically porous, active carbon of high graphitization (HPCHG), which demonstrated superior performance as the electrode in both SCs and SIBs. An iron-containing organometallic coordination compound was used as the carbon precursor, and the iron in the molecular framework also functioned as a catalyst to promote the carbonization at low temperatures. In combination with molten salt activation, a low pyrolysis temperature of 600 °C was required, and the asobtained carbon material showed high specific area (>1200 m2 g−1), increased density of surface defects, yet high graphitization. The electrochemical measurements show that a high gravimetric capacitance of 250 F g−1 was reached as the EDLCtype electrode for SCs. Besides, when used as an anode in

■

RESULTS AND DISCUSSION The strategy for facile synthesis of hierarchically porous carbon of high graphitization (HPCHG) is schematically presented in Figure 1. The carbon precursor, iron(III) acetylacetonate (Fe(acac)3), is an organometallic coordination compound with unique structural features: every Fe atom in the structure is coordinated by three acetylacetone ligands. As reported previously, Fe is a favorable catalyst for carbonization and graphitization of organic substances.25−29 Accordingly, the iron in the Fe(acac)3 structure acted as a catalyst to promote the carbonization of the organic ligands and graphitization of the resulting carbon at relatively low temperatures. On the other hand, molten zinc chloride (ZnCl2) played several roles during the process. First, it acted as a heating media of large thermal capacity (typical heat capacity of ZnCl2 is 80.79 J/mol at 600 °C)30 to provide homogeneous heating of the carbon precursor to the desired temperature for the endothermic carbonization reaction. Second, the molten salt acted as a soft template to introduce pores to the in situ formed carbon, as confirmed in our previous studies.31−33 Third, the molten salt acted as a B


Research Article


Figure 3. (a) X-ray diffraction (XRD) result of the HPCHG sample. The inset is the TEM picture showing the selected area electron diffraction (SAED) pattern. (b) Raman spectra of the HPCHG sample. (c) X-ray photoelectron spectroscopy (XPS) and (d) high resolution of the C 1s spectrum of HPCHG.

molten ZnCl2 activation shows a morphology similar to that of HPCHG (Figure S2); however, the degree of graphitization was much lower. No obvious lattice fringes are found in the HR-TEM image of the HPC sample (Figure S3), which suggests that the nanoporous structure of the carbon is attributed to the templating effect of the molten salt, whereas the high degree of graphitization is due to the catalytic effect of the Fe ions. Next, the microstructural features of the various samples were investigated by nitrogen adsorption/desorption isotherms shown in Figure 2f and Figure S4. The high intercept of HPCHG at P/Po is close to 0, which suggests the presence of abundant micropores in its structure, and the high rise at high P/Po indicates the presence of rich meso- or macropores. The specific surface area for the HPCHG sample, calculated from the isotherms, is ∼1134 m2 g−1. According to the BJH plot in the inset of Figure 2f, the total pore volume (VTotal) of the sample is ∼1.99 cm3 g−1, and the average pore diameter (DAverage) is about 7.0 nm. These structural features allow easy penetration of the liquid electrolyte for fast interface reaction when used as an electrode for SC and SIB. Interestingly, the HPC sample shows an even higher specific surface area of 1430 m2 g−1 compared to the HPCHG sample (Figure S4a), providing an indirect support that iron is a good catalyst for graphitization of carbon. Instead, the carbon of high graphitization (CHG) shows a much lower specific surface area (377 m2 g−1), implying the importance of molten salt activation to increasing the specific surface area. Both soft templating and surface corrosion effects from the molten salt likely contributed to the improved specific surface area of the HPCHG and HPC samples compared with the CHG.31,37−39 The phase structure of the as-prepared HPCHG sample was investigated by X-ray diffraction (XRD) characterization. The

corrosive medium to create surface defects over the as-formed carbon material. Finally, the molten salt also functioned as an inhibitor to suppress aggregation of carbon during calcination. Thus, the combined catalytic effect of Fe ions and the other effects of the molten salt resulted in hierarchically porous carbon of high graphitization. The typical yield of the porous carbon material is ∼23 wt % (after washing away all the metal residues) calculated by the total mass of the raw material iron(III) acetylacetonate. It will be ∼39 wt % if we calculate the yield relying on only the total carbon atoms in the synthesis process. Compared to the typical carbon yield of 28−40% as reported in the literature,34−36 our yields are sufficient for the large-scale production of hierarchical porous carbon materials. The morphologies of the as-synthesized carbon samples were first examined under SEM in Figure 2a−c. The HPCHG sample is made up of loosely packed particles with diameters ranging from 0.3 to 1.0 μm. A closer look at these fine particles reveals that they were mainly constructed from randomly crosslinked carbon frameworks with abundant nanopores. Such a morphological structure resembles a foam-like porous carbon structure. The corresponding transmission electron microscopy (TEM) images in Figure 2d present that the foam-like carbon was constructed from carbon filaments with diameters of 3−8 nm, which were severely entangled to create plenty of nanopores. Lattice fringes in the curved carbon are clearly seen in the high-resolution TEM (HR-TEM) image shown in Figure 2e, suggesting the existence of graphitic carbon domains in the as-synthesized products. In contrast, the graphitized carbon prepared without ZnCl2 activation (SEM image shown in Figure S1) is composed of thick and curved carbon rods with a diameter of several hundred nanometers. The hierarchically porous carbon (HPC) sample prepared using zinc(II) acetylacetonate as the carbon precursor in combination with C


Research Article


Figure 4. (a) Cyclic voltammetry (CV) plot of HPCHG at 5−200 mV s−1. (b) CV plots of different samples at 100 mV s−1. (c) Galvanostatic charge/discharge curves of HPCHG at different current densities. (d) Galvanostatic charge/discharge curves of different samples at a high current density of 30 A g−1. The inset picture reveals the current−resistance (I−R) drop during the charge/discharge cycles. (e) Rate performances of different carbon samples at various current densities (0.5−50 A g−1). (f) Long-term test of the HPCHG electrode for 10 000 cycles at a current density of 8 A g−1.

Fe2O3 further reacted with ZnO to form a more stable ZnFe2O4 spinel phase. Thus, mixed phases of ZnFe2O4 and ZnO were observed in Figure S5a.42,43 Interestingly, the iron was further converted to metallic iron and Fe3C in the CHG sample (Figure S5e), which implies the critical role of molten ZnCl2 in the formation of the oxide phases. It is likely that without the application of molten ZnCl2 the oxygen-contained gaseous intermediates from the thermal decomposition of organic ligands quickly escaped to the surrounding atmosphere, whereas by applying molten ZnCl2, the oxygen was well confined in the molten salt media and immediately reacted with surrounding ZnCl2 to form ZnO.39 As a result, different compositions of iron-based products were observed in the HPCHG, HPC, and CHG samples in Figure S5a, c, and e. The XRD patterns of the HPCHG, HPC, and CHG samples after acid washing exhibit a position shift of the (002) diffraction plane. The average interlayer distance of HPCHG (0.354 nm) is larger than the graphite-like CHG sample (daverage = 0.337 nm). As demonstrated by HR-TEM in Figure 2e, the graphitic domain already appeared in the HPCHG sample even at a low pyrolysis temperature of 600 °C. The graphitization degree of the related samples was further characterized by Raman spectroscopy with the results shown in Figure 3b and Figure

XRD pattern of HPCHG in Figure 3 demonstrated two broad peaks at 2-theta of approximately 25.3° and 43.4°, which can be assigned to the (002) and (100) crystallographic planes in a disordered carbon structure, indicating the formation of a pure carbon material. No trace of iron residues was detected, which suggests the successful elimination of the iron catalyst after the acid wash. The corresponding selected area electron diffraction (SAED) pattern also provides the concentric rings of the (002) and (100) lattice planes. To understand the carbonization mechanism during the molten-salt-assisted calcination process, XRD patterns of HPCHG, CHG, and HPC before and after the acid wash process are comparatively studied with the results presented in Figure S5. Before the acid wash, the HPCHG sample demonstrated a mixture of crystalline phases of ZnFe2O4 (PDF 089-7412) and ZnO (PDF 079-0207). The HPC sample showed mainly the crystalline phase of ZnO, whereas the CHG sample demonstrated the main compositions of metallic Fe (PDF 065-4899) and Fe3C (PDF 034-0001). Before acid washing, the oxygen in ZnO/ZnFe2O4 in the HPCHG and HPC samples originates from the acetylacetonate ligands since only the acetylacetonate ligands contain oxygen atoms. The taking up of oxygen from the acac ligands with the formation of Fe2O3 and ZnO then promoted the formation of graphitic carbon material.39−41 In HPCHG, the as-produced D


Research Article


an aqueous electrolyte of 6 M KOH. For comparison, both HPC and CHG were evaluated. Figure 4a presents cyclic voltammetry (CV) curves of the HPCHG electrode at scan rates that range from 5 to 200 mV s−1. The quasi-rectangular shape of all the CV curves and stable high current density response indicate excellent electrochemical behavior and high stability of its unique porous structure, surface defects, and surface functional groups. In Figure 4b, HPCHG had the largest I−V response area among the three electrodes of HPCHG, HPC, and CHG in their CVs at a scan rate of 100 mV s−1. From Figure 4c, the quasi-triangular shape of the curves with distinct distortion suggests that, in addition to the main capacitance from EDLC, a certain amount of pseudocapacitance also appeared, which could be ascribed to surface reactions that involve functional O-containing groups.54,55 According to Figure 4d, the HPCHG electrode demonstrated the largest charge storage capacity and the smallest IR drops among the three electrodes at 30 A g−1. Here, the specific capacitances in SCs were calculated by the following equation

S6. For comparison, the commercial graphite and activated carbon (XFP01, XF NANO) with surface areas of 1800 m2 g−1 were also measured. All three samples showed two characteristic peaks at ∼1340 and ∼1580 cm−1, which are typically recognized as the D and G band for carbon materials.44,45 To be specific, the D band originated from defected and disordered carbon, whereas the G band is related to the graphitic part inside the carbon. The graphitization of the sample can be revealed by the intensity ratio value of the D and G peak (ID/ IG), which was obtained from the Raman spectra by applying the Lorentz fitting method.33,45,46 For the graphite sample, an ID/IG value of 0.16 was demonstrated, which is in good agreement with the numbers reported in the literature,47,48 whereas the value for the activated carbon was found to be 1.26. ID/IG values of 0.88, 0.73, and 1.02 were calculated from the Raman spectra of the HPCHG, CHG, and HPC samples, respectively. The above results clearly suggest a high graphitization of HPCHG and CHG samples despite a low pyrolysis temperature of 600 °C, which is even lower than previous reports for iron catalysts (700−850 °C).26,27,29,49 We believe that a better catalytic effect was provided by the atom level dispersion of Fe in the carbon precursor (iron(III) acetylacetonate) to result in a more efficient carbonization process. The smaller ID/IG value of CHG compared with HPCHG is an indicator of increased surface defects from molten ZnCl2 etching, whereas the larger ID/IG value of the HPC sample compared with the HPCHG sample implies that Fe is a much better atom catalyst than Zn for the graphitization of carbon. The surface functional group of carbon can contribute to capacitive energy storage; however, its stability is a large concern. X-ray photoelectron spectroscopy (XPS) was also carried out to reveal the surface composition and chemical bond of the HPCHG sample in Figure 3c. The results confirm that HPCHG is a pure carbon material without any metal residues. In addition, the sample demonstrated low surface oxygen content of only 5.4 wt %, which is lower than most of the hard carbon materials that are synthesized at 0.370 nm is required for the successful intercalation of Na+ into the graphite interlayers,19 the capacitive energy storage maintains a critical role for the Na+ storage in HPCHG anodes. Further investigation on the series of CV curves shown in Figure 5a provides information regarding the Na+ storage mechanism (by

through 10 000 cycles, which shows highly stable cycling performance. The HPCHG sample was further tested for its performance as an anode in SIBs. A cyclic voltammogram (CV) of the sodium-ion coin cell with a HPCHG anode was first investigated, and the results are presented as an inset in Figure S8. Two irreversible peaks at 0.95 and 0.24 V appeared in the CV curves from the initial cathodic process, which is related to the decomposition of the PC-based electrolyte on the active surfaces with the formation of a stable solid−electrolyte interphase (SEI) and irreversible sodium insertion into the F


Research Article


oxygen-containing surface groups during repeated Na+ storage and release. Figure 6d displays the EIS plots of HPCHG which were obtained at various discharging potentials. The charge transfer resistance as indicated by the diameter of the impedance loop in the plot decreases at lower voltages. The decrease in charge transfer resistance suggests that improved sodium-ion transfer kinetics was achieved by adsorption of Na+ onto the active surfaces of the HPCHG electrode. The sodium-ion diffusion coefficient of the electrode is also calculated based on the EIS results according to the equations listed in the Supporting Information, and the calculated Warburg factor (σ) and sodium-ion diffusion coefficient (DNa) at different stages of discharge are listed in Table S3. The results show that the Na+ diffusion coefficient of HPCHG electrode attains 3.45 × 10−10 cm2 s−1 at a fully discharged state of 0.01 V, which is higher than other newly synthesized carbon materials reported in the literatures (Table S4) and further supports the superior rate performance presented in Figure 6b. Moreover, the long-term cycling performance provided in Figure 6e at a high current density of 5000 mA g−1 indicates that the Na+ storage in HPCHG is highly reversible. The capacity remains to be 98.6 mA h g−1 even after 2000 cycles with almost 100% Coulombic efficiency of every cycle after the initial several cycles of activation. These data further confirm that HPCHG has efficient Na+ diffusion kinetics, robust frameworks, and high Na+ storage capacity, which is promising as an electrode for fast energy storage and conversion.

Faradaic sodium insertion/extraction or by capacitive sodium storage), which is related to the following equation:24,61,62 i = avb

(2)

In this equation, a and b represent the kinetic-related coefficient values. To be specific, the linear correlation of i and ν (b = 1) implies an ideal capacitive process, and a proportional correlation between i and ν0.5 (b = 0.5) indicates a diffusiondominant process and can be assigned to Faradaic Na+ insertion/extraction. In Figure 5b, the b value of the HPCHG sample is calculated to be 0.81 at 0.01 V, which confirms that the capacitive sodium storage makes the biggest contributions on the whole capacity. In addition, the contribution source of the total charge (Q) from CV results can be further considered to be two parts:24,63 Q = Qd + Qs

(3)

Qd is the charge resulting from the diffusion-dominant process, and Qs is the charge from the surface capacitive storage. If the semi-infinite linear diffusion model is applied, the relationship between ν and Qd is described in the following equation

Q = cv−1/2 + Q s

(4)

As a note, c represents a constant related to diffusion coefficient. As a result, the capacitive contribution can be estimated by extrapolating the relationship between the normalized capacities (Q) against v−1/2. From Figure 5c, the extrapolated y-intercept can be calculated as ∼52.2%, which shows the critical contribution of capacitive storage to the HPCHG sample.24 The charge/discharge curves of the HPCHG anode at various current densities and the corresponding rate performances were further studied with the results shown in Figure 6a,b. The electrode delivered favorable specific capacities of 322, 207, 171, 156, 150, 131, and 118 mA h g−1 with the constant current densities of 100, 200, 500, 800, 1000, 2000, and 3000 mA g−1, respectively. Even at a very large current density of 5000 mA g−1, a specific capacity of 101 mA h g−1 was still achieved, which is higher than that of most of the previous carbonaceous anodes for SIBs that were discharged at similar discharge current density (Table S2). The advantageous feature of capacitive Na+ storage was further demonstrated. It is wellknown that the capacitive process contains a double-layer capacitance with fast ion diffusion and superior structural stability, and the surface-induced Na+ storage can promote fast charge/discharge abilities by facilitating the adsorption of Na+ onto nanovoids as well as surface defects/functional groups. On the other hand, the controlled HPC sample had similar specific capacities at low rates but with a serious capacity decay at higher charge−discharge current densities, which proves a critical effect in graphitization degree on the rate performance and shows the instability of excess oxygen-containing functional groups during the Na+ absorption/desorption. Moreover, the CHG sample exhibited a lower sodium storage capability, which could be due to the lack of sufficient active sites that result from lower surface areas. In Figure 6c, after full activation by the initial ten cycles, the HPCHG electrode demonstrated a stable specific capacity of 170 mA h g−1 at 500 mA g−1 during the following 270 cycles. However, for the HPC sample, the capacity started to fade after approximately 70 cycles, which possibly resulted from the unstable surface reaction with rich

■

CONCLUSIONS In conclusion, hierarchical porous carbon of high graphitization was successfully fabricated at a low pyrolysis temperature of 600 °C by taking the advantages of an Fe-containing carbon precursor in a molten-salt-assisted carbonization process. The obtained HPCHG material exhibited promising electrochemical performance when used as the electrode in an SC and a rechargeable SIB, provided by the effective pathways for rapid ion and electron transport from the well-tailored microstructure. When tested in a supercapacitor, the HPCHG displayed a specific capacitance of 248 F g−1 at 0.5 A g−1 and minimal capacity decay after 10 000 cycles at 8 A g−1. When tested in a SIB, the HPCHG electrode showed excellent rate performance with a reversible capacity of 322 mA h g−1 at 100 mA g−1 and a superior capacity of 101 mA h g−1 even at 5000 mA g−1. In addition, it displayed a stable cycling performance for 2000 cycles, suggesting that HPCHG has the potential to be one of the most promising electrode materials for highperformance energy storage devices.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b04733. The experimental method, additional material characterization results, additional TEM, XPS, SEM, BET, and XRD results of as-synthesized materials, electrode fabrication and electrochemical test methods, cyclic voltammetry, cycling stability and Galvanostatic charge/ discharge plot of HPCHG sample, tables listing the comparison of HPCHG material with the performances of the other recently reported anodes, and detailed G


Research Article


■

ance Anode Material for Sodium-Ion Batteries. Adv. Energy Mater. 2016, 6, 1600659. (14) Liang, Z.; Qu, C.; Guo, W.; Zou, R.; Xu, Q. Pristine MetalOrganic Frameworks and their Composites for Energy Storage and Conversion. Adv. Mater. 2017, 1702891. (15) Qu, C.; Zhao, B.; Jiao, Y.; Chen, D.; Dai, S.; deglee, B. M.; Chen, Y.; Walton, K. S.; Zou, R.; Liu, M. Functionalized Bimetallic Hydroxides Derived from Metal-Organic Frameworks for HighPerformance Hybrid Supercapacitor with Exceptional Cycling Stability. ACS Energy Letters 2017, 2, 1263−1269. (16) Xia, W.; Qu, C.; Liang, Z.; Zhao, B.; Dai, S.; Qiu, B.; Jiao, Y.; Zhang, Q.; Huang, X.; Guo, W.; Dang, D.; Zou, R.; Xia, D.; Xu, Q.; Liu, M. High-Performance Energy Storage and Conversion Materials Derived from a Single Metal-Organic Framework/Graphene Aerogel Composite. Nano Lett. 2017, 17, 2788−2795. (17) 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.; Su, D.; Stach, E. A.; Ruoff, R. S. Carbon-based Supercapacitors Produced by Activation of Graphene. Science 2011, 332, 1537−1541. (18) Wen, Y.; He, K.; Zhu, Y.; Han, F.; Xu, Y.; Matsuda, I.; Ishii, Y.; Cumings, J.; Wang, C. Expanded Graphite as Superior Anode for Sodium-ion Batteries. Nat. Commun. 2014, 5, 4033. (19) Cao, Y.; Xiao, L.; Sushko, M. L.; Wang, W.; Schwenzer, B.; Xiao, J.; Nie, Z.; Saraf, L. V.; Yang, Z.; Liu, J. Sodium Ion Insertion in Hollow Carbon Nanowires for Battery Applications. Nano Lett. 2012, 12, 3783−3787. (20) Song, H.; Li, N.; Cui, H.; Wang, C. Enhanced Storage Capability and Kinetic Processes by Pores- and Hetero-atoms-riched Carbon Nanobubbles for Lithium-ion and Sodium-ion Batteries Anodes. Nano Energy 2014, 4, 81−87. (21) Xiao, L.; Cao, Y.; Henderson, W. A.; Sushko, M. L.; Shao, Y.; Xiao, J.; Wang, W.; Engelhard, M. H.; Nie, Z.; Liu, J. Hard Carbon Nanoparticles as High-capacity, High-stability Anodic Materials for Na-ion Batteries. Nano Energy 2016, 19, 279−288. (22) Yang, Y.; Tang, D.-M.; Zhang, C.; Zhang, Y.; Liang, Q.; Chen, S.; Weng, Q.; Zhou, M.; Xue, Y.; Liu, J.; Wu, J.; Cui, Q. H.; Lian, C.; Hou, G.; Yuan, F.; Bando, Y.; Golberg, D.; Wang, X. Protrusions” or “Holes” in Graphene: Which is the Better Choice for Sodium Ion Storage? Energy Environ. Sci. 2017, 10, 979−986. (23) Chen, C.; Wen, Y.; Hu, X.; Ji, X.; Yan, M.; Mai, L.; Hu, P.; Shan, B.; Huang, Y. Na(+) Intercalation Pseudocapacitance in Graphenecoupled Titanium Oxide Enabling Ultra-fast Sodium Storage and Long-term Cycling. Nat. Commun. 2015, 6, 6929. (24) Li, S.; Qiu, J.; Lai, C.; Ling, M.; Zhao, H.; Zhang, S. Surface Capacitive Contributions: Towards High Rate Anode Materials for Sodium Ion Batteries. Nano Energy 2015, 12, 224−230. (25) Krivoruchko, O. P.; Zaikovskii, V. I. A New Phenomenon Involving the Formation of Liquid Mobile Metal-carbon Particles in the Low-temperature Catalytic Graphitisation of Amorphous Carbon by Metallic Fe, Co and Ni. Mendeleev Commun. 1998, 3, 97−100. (26) Hoekstra, J.; Beale, A. M.; Soulimani, F.; Versluijs-Helder, M.; Geus, J. W.; Jenneskens, L. W. Base Metal Catalyzed Graphitization of Cellulose: A Combined Raman Spectroscopy, Temperature-Dependent X-ray Diffraction and High-Resolution Transmission Electron Microscopy Study. J. Phys. Chem. C 2015, 119, 10653−10661. (27) Hoekstra, J.; Beale, A. M.; Soulimani, F.; Versluijs-Helder, M.; van de Kleut, D.; Koelewijn, J. M.; Geus, J. W.; Jenneskens, L. W. The Effect of Iron Catalyzed Graphitization on the Textural Properties of Carbonized Cellulose: Magnetically Separable Graphitic Carbon Bodies for Catalysis and Remediation. Carbon 2016, 107, 248−260. (28) Gutiérrez-Pardo, A.; Ramírez-Rico, J.; Cabezas-Rodríguez, R.; Martínez-Fernández, J. Effect of Catalytic Graphitization on the Electrochemical Behavior of Wood Derived Carbons for Use in Supercapacitors. J. Power Sources 2015, 278, 18−26. (29) Suzuki, T.; Matsuzaki, H.; Suzuki, K.; Saito, Y.; Yasui, S.-i.; Okazaki, N.; Yamada, T. High Electroconductivity of Wood Char Obtained by Iron-catalyzed Carbonization. Chem. Lett. 2008, 37, 798− 799.

sodium-ion diffusion coefficient calculation method (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (Zongping Shao). *E-mail: [email protected] (Meilin Liu). ORCID

Wei Zhou: 0000-0003-0322-095X Meilin Liu: 0000-0002-6188-2372 Zongping Shao: 0000-0002-4538-4218 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The work was supported by the Six Talent Peaks Project of Jiangsu Province under contract No. XNY-CXTD-001, the National Nature Science Foundation of China under contract No. 21576135, and the Priority Academic Program Development of Jiangsu Higher Education Institutions, Jiangsu Natural Science Foundation for Distinguished Young Scholars under contract No. BK20170043. Xiang Deng acknowledges the international learning funding from Nanjing Tech University.

■

REFERENCES

(1) Zhao, B.; Ran, R.; Liu, M.; Shao, Z. A Comprehensive Review of Li4Ti5O12-based Electrodes for Lithium-ion Batteries: The Latest Advancements and Future Perspectives. Mater. Sci. Eng., R 2015, 98, 1−71. (2) Xia, G.; Zhang, L.; Fang, F.; Sun, D.; Guo, Z.; Liu, H.; Yu, X. General Synthesis of Transition Metal Oxide Ultrafine Nanoparticles Embedded in Hierarchically Porous Carbon Nanofibers as Advanced Electrodes for Lithium Storage. Adv. Funct. Mater. 2016, 26, 6188− 6196. (3) Yabuuchi, N.; Kubota, K.; Dahbi, M.; Komaba, S. Research Development on Sodium-ion Batteries. Chem. Rev. 2014, 114, 11636− 11682. (4) Wang, Q.; Yan, J.; Fan, Z. Carbon Materials for High Volumetric Performance Supercapacitors: Design, Progress, Challenges and Opportunities. Energy Environ. Sci. 2016, 9, 729−762. (5) Palomares, V.; Serras, P.; Villaluenga, I.; Hueso, K. B.; CarreteroGonzález, J.; Rojo, T. Na-ion Batteries, Recent Advances and Present Challenges to Become Low Cost Energy Storage Systems. Energy Environ. Sci. 2012, 5, 5884−5901. (6) Slater, M. D.; Kim, D.; Lee, E.; Johnson, C. S. Sodium-ion Batteries. Adv. Funct. Mater. 2013, 23, 947−958. (7) Xia, G.; Gao, Q.; Sun, D.; Yu, X. Porous Carbon Nanofibers Encapsulated with Peapod-Like Hematite Nanoparticles for High-Rate and Long-Life Battery Anodes. Small 2017, 13, 1701561. (8) Simon, P.; Gogotsi, Y. Materials for Electrochemical Capacitors. Nat. Mater. 2008, 7, 845−854. (9) Kim, S. W.; Seo, D. H.; Ma, X.; Ceder, G.; Kang, K. Electrode Materials for Rechargeable Sodium-Ion Batteries: Potential Alternatives to Current Lithium-Ion Batteries. Adv. Energy Mater. 2012, 2, 710−721. (10) Dunn, B.; Kamath, H.; Tarascon, J. M. Electrical Energy Storage for the Grid: A Battery of Choices. Science 2011, 334, 928−935. (11) Armand, M.; Tarascon, J. M. Building Better Batteries. Nature 2008, 451, 652−657. (12) Hwang, J. Y.; Li, M.; El-Kady, M. F.; Kaner, R. B. NextGeneration Activated Carbon Supercapacitors: A Simple Step in Electrode Processing Leads to Remarkable Gains in Energy Density. Adv. Funct. Mater. 2017, 27, 1605745. (13) Li, Y.; Hu, Y.-S.; Titirici, M.-M.; Chen, L.; Huang, X. Hard Carbon Microtubes Made from Renewable Cotton as High-PerformH


Research Article

ACS Applied Materials & Interfaces (30) Cubicciotti, D.; Eding, H. Heat Contents of Molten Zinc Chloride and Bromide and the Molecular Constants of the Gases. J. Chem. Phys. 1964, 40, 978−982. (31) Deng, X.; Zhao, B.; Zhu, L.; Shao, Z. Molten Salt Synthesis of Nitrogen-doped Carbon with Hierarchical Pore Structures for Use as High-performance Electrodes in Supercapacitors. Carbon 2015, 93, 48−58. (32) Deng, X.; Zhao, B.; Sha, Y.; Zhu, Y.; Xu, X.; Shao, Z. Three Strongly Coupled Allotropes in a Functionalized Porous All-Carbon Nanocomposite as a Superior Anode for Lithium-Ion Batteries. ChemElectroChem 2016, 3, 698−703. (33) Deng, X.; Zhao, B.; Zhong, Y.; Zhu, Y.; Shao, Z. Rational Confinement of Molybdenum Based Nanodots in Porous Carbon for Highly Reversible Lithium Storage. J. Mater. Chem. A 2016, 4, 10403− 10408. (34) Ahmadpour, A.; Do, D. D. The Preparation of Activated Carbon from Macadamia Nutshell by Chemical Activation. Carbon 1997, 35, 1723−1732. (35) Salitra, G.; Soffer, A.; Eliad, L.; Cohen, Y.; Aurbach, D. Carbon Electrodes for Double-layer Capacitors - I. Relations Between Ion and Pore Dimensions. J. Electrochem. Soc. 2000, 147, 2486−2493. (36) Kennedy, L. J.; Vijaya, J. J.; Sekaran, G. Effect of Two-stage Process on the Preparation and Characterization of Porous Carbon Composite from Rice Husk by Phosphoric Acid Activation. Ind. Eng. Chem. Res. 2004, 43, 1832−1838. (37) Ouyang, T.; Cheng, K.; Gao, Y.; Kong, S.; Ye, K.; Wang, G.; Cao, D. Molten Salt Synthesis of Nitrogen Doped Porous Carbon: a New Preparation Methodology for High-Volumetric Capacitance Electrode Materials. J. Mater. Chem. A 2016, 4, 9832−9843. (38) Fellinger, T. P.; Thomas, A.; Yuan, J.; Antonietti, M. 25th Anniversary Article: ″Cooking Carbon with Salt″: Carbon Materials and Carbonaceous Frameworks from Ionic Liquids and Poly(ionic liquid)s. Adv. Mater. 2013, 25, 5838−5854. (39) Liu, X. Ionothermal Synthesis of Carbon Nanostructures: Playing with Carbon Chemistry in Inorganic Salt Melt. Nano Adv. 2016, 1, 90−103. (40) Cesano, F.; Scarano, D.; Bertarione, S.; Bonino, F.; Damin, A.; Bordiga, S.; Prestipino, C.; Lamberti, C.; Zecchina, A. Synthesis of ZnO-carbon Composites and Imprinted Carbon by the Pyrolysis of ZnCl2-catalyzed Furfuryl Alcohol Polymers. J. Photochem. Photobiol., A 2008, 196, 143−153. (41) Ahmadpour, A.; Do, D. D. The Preparation of Active Carbons from Coal by Chemical and Physical Activation. Carbon 1996, 34, 471−479. (42) Zou, F.; Hu, X.; Li, Z.; Qie, L.; Hu, C.; Zeng, R.; Jiang, Y.; Huang, Y. MOF-derived Porous ZnO/ZnFe(2)O(4)/C Octahedra with Hollow Interiors for High-rate Lithium-ion Batteries. Adv. Mater. 2014, 26, 6622−6628. (43) McDonald, K. J.; Choi, K.-S. Synthesis and Photoelectrochemical Properties of Fe2O3/ZnFe2O4Composite Photoanodes for Use in Solar Water Oxidation. Chem. Mater. 2011, 23, 4863−4869. (44) Xu, J.; Wang, M.; Wickramaratne, N. P.; Jaroniec, M.; Dou, S.; Dai, L. High-performance Sodium Ion Batteries Based on a 3D Anode from Nitrogen-doped Graphene Foams. Adv. Mater. 2015, 27, 2042− 2048. (45) Zhou, Y.; Candelaria, S. L.; Liu, Q.; Uchaker, E.; Cao, G. Porous Carbon with High Capacitance and Graphitization through Controlled Addition and Removal of Sulfur-containing Compounds. Nano Energy 2015, 12, 567−577. (46) Song, L.-J.; Liu, S.-S.; Yu, B.-J.; Wang, C.-Y.; Li, M.-W. Anode Performance of Mesocarbon Microbeads for Sodium-ion Batteries. Carbon 2015, 95, 972−977. (47) Xing, T.; Li, L. H.; Hou, L.; Hu, X.; Zhou, S.; Peter, R.; Petravic, M.; Chen, Y. Disorder in Ball-milled Graphite Revealed by Raman Spectroscopy. Carbon 2013, 57, 515−519. (48) Pimenta, M. A.; Dresselhaus, G.; Dresselhaus, M. S.; Cancado, L. G.; Jorio, A.; Saito, R. Studying Disorder in Graphite-based Systems by Raman Spectroscopy. Phys. Chem. Chem. Phys. 2007, 9, 1276−1291.

(49) Thompson, E.; Danks, A. E.; Bourgeois, L.; Schnepp, Z. Ironcatalyzed Graphitization of Biomass. Green Chem. 2015, 17, 551−556. (50) Zhang, P.; Qiao, Z.-A.; Zhang, Z.; Wan, S.; Dai, S. Mesoporous Graphene-like Carbon Sheet: High-power Supercapacitor and Outstanding Catalyst Support. J. Mater. Chem. A 2014, 2, 12262−12269. (51) Liu, X.; Giordano, C.; Antonietti, M. A Facile Molten-salt Route to Graphene Synthesis. Small 2014, 10, 193−200. (52) Zhou, J.-H.; Sui, Z.-J.; Zhu, J.; Li, P.; Chen, D.; Dai, Y.-C.; Yuan, W.-K. Characterization of Surface Oxygen Complexes on Carbon Nanofibers by TPD, XPS and FT-IR. Carbon 2007, 45, 785−796. (53) Zielke, U.; Hüttinger, K.; Hoffman, W. Surface-oxidized Carbon Fibers: I. Surface Structure and Chemistry. Carbon 1996, 34, 983−998. (54) Zhu, K.; Wang, Y.; Tang, J. A.; Guo, S.; Gao, Z.; Wei, Y.; Chen, G.; Gao, Y. A High-performance Supercapacitor Based on Activated Carbon Fibers with An Optimized Pore Structure and Oxygencontaining Functional Groups. Mater. Chem. Front. 2017, 1, 958−966. (55) Yoon, Y.; Lee, K.; Baik, C.; Yoo, H.; Min, M.; Park, Y.; Lee, S. M.; Lee, H. Anti-solvent Derived Non-stacked Reduced Graphene Oxide for High Performance Supercapacitors. Adv. Mater. 2013, 25, 4437−4444. (56) Gogotsi, Y.; Simon, P. True Performance Metrics in Electrochemical Energy Storage. Science 2011, 334, 917−918. (57) Zhu, Y.; Murali, S.; Stoller, M. D.; Ganesh, K.; Cai, W.; Ferreira, P. J.; Pirkle, A.; Wallace, R. M.; Cychosz, K. A.; Thommes, M. Carbonbased Supercapacitors Produced by Activation of Graphene. Science 2011, 332, 1537−1541. (58) Wang, Y.-X.; Chou, S.-L.; Liu, H.-K.; Dou, S.-X. Reduced Graphene Oxide with Superior Cycling Stability and Rate Capability for Sodium Storage. Carbon 2013, 57, 202−208. (59) Tang, K.; Fu, L.; White, R. J.; Yu, L.; Titirici, M.-M.; Antonietti, M.; Maier, J. Hollow Carbon Nanospheres with Superior Rate Capability for Sodium-Based Batteries. Adv. Energy Mater. 2012, 2, 873−877. (60) Wang, H. G.; Wu, Z.; Meng, F. L.; Ma, D. L.; Huang, X. L.; Wang, L. M.; Zhang, X. B. Nitrogen-doped Porous Carbon Nanosheets as Low-cost, High-performance Anode Material for Sodium-ion Batteries. ChemSusChem 2013, 6, 56−60. (61) Wang, J.; Polleux, J.; Lim, J.; Dunn, B. Pseudocapacitive Contributions to Electrochemical Energy Storage in TiO2 (Anatase) Nanoparticles. J. Phys. Chem. C 2007, 111, 14925−14931. (62) Augustyn, V.; Simon, P.; Dunn, B. Pseudocapacitive Oxide Materials for High-rate Electrochemical Energy Storage. Energy Environ. Sci. 2014, 7, 1597−1614. (63) Augustyn, V.; Come, J.; Lowe, M. A.; Kim, J. W.; Taberna, P. L.; Tolbert, S. H.; Abruna, H. D.; Simon, P.; Dunn, B. High-rate Electrochemical Energy Storage Through Li+ Intercalation Pseudocapacitance. Nat. Mater. 2013, 12, 518−522.

I


A Facile Strategy to Low-Cost Synthesis of Hierarchically Porous

Recommend Documents