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Hierarchical porous biochar derived from cotinus coggygria flower by using a novel composite activator for supercapacitors
Chemical Physics Letters 747 (2020) 137325
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Research paper
Hierarchical porous biochar derived from cotinus coggygria flower by using a novel composite activator for supercapacitors ⁎
Yanhong Lia, Xin Zhangb, , Jiaying Denga, Xiaheng Yanga, Jinlong Wanga, Yanzhi Wanga,
T
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a Hebei Key Laboratory of Applied Chemistry, Hebei Key Laboratory of Heavy Metal Deep-remediation in Water and Resource Reuse, School of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao, Hebei 066004, China b Hubei Key Laboratory of Low Dimensional Optoelectronic Materials and Devices, Hubei University of Arts and Science, Xiangyang 441053, China
H I GH L IG H T S
hierarchical porous biochar has been prepared from cotinus coggygria flower. • The composite activator has been developed to synthesize the biochar. • AThenovel delivers the high specific capacitance in 1 M H2SO4 electrolyte. • The biochar • biochar exhibits the stable cycling performance in 6 M KOH electrolyte.
A R T I C LE I N FO
A B S T R A C T
Keywords: Energy storage and conversion Biomaterials Hierarchical porous Cotinus coggygria flowers Composite activator
Hierarchical porous biochar with large BET surface area of 959.04 cm2 g−1 was synthesized by using a novel composite activator from cotinus coggygria flowers. The biochar delivers excellent specific capacitance of 413.5 F g−1 at current density of 0.5 A g−1 in 1 M H2SO4 electrolyte and a well reversible capacitance of 279.9 F g−1 at current density of 5 A g−1 in 6 M KOH electrolyte after 36,000 cycles. The excellent specific capacitance and the stable cycling performance benefit from the synergism of the composite activator. This provides a meaningful reference for the synthesis of supercapacitor biomaterials.
1. Introduction In recent years, a growing number of research workers are jioning the rush to research supercapacitors. Compared with batteries, supercapacitors possess high power density, superior cycling performance and short charging time [1]. Biochar materials are promising become electrode materials for supercapacitors because of their low costs, good safeties and high electrical conductivities [2–4]. The methods for preparing such materials include direct carbonization method, hydrothermal method, and activation method. Activation methods are classified into physical activation and chemical activation [5,6]. KOH [7,8], NaOH [9], ZnCl2 [10], KCl [11], HNO3 [3] and H3PO4 [12] are commonly used as chemical activation reagents. Many researchers have a higher evaluation of KOH because electrode materials prepared with KOH as an activator tend to have higher specific capacitance. For instance, Yu et al. [13] reported a porous carbon material derived from phoenix seeds, which showed 376 F g−1 specific capacitance in 2 M H2SO4 aqueous solution at 0.5 A g−1. Xie et al. [14] fabricated a porous carbon microtube by willow catkins with activation of KOH, which ⁎
presented 292 F g−1 specific capacitance at 1 A g−1. Although KOHactivated biomass carbon delivers a high specific capacity, KOH acts as a base and inevitably pollutes the environment during post-treatment. It is well known that biomass as a carbon source has been widely used in the study of electrode materials. Biomass is a low-cost, renewable raw material, which can be turned into a treasure after a series of experimental treatments [3]. Biochar is an emerging carbon material formed from biomass raw materials through a series of processes [15]. Meanwhile, biochar has the advantages of high specific surface area, abundant pores, and well electrical conductivity [4]. Many biomass have been used to make biomass charcoal, such as fruit peels [16], peanut shell [17], walnut shell [11], barley straw [6], animal waste [18,19], rice husk [20], and so on. Cotinus coggygria, normally known as the “Smoke Tree”, is distributed in southern Europe, central Asia, from the Himalaya to northern China. Wild cotinus coggygria is a resource plant with great utilization value. Cotinus coggygria is widely used in medicine due to its antibacterial, anti-inflammatory and anti-bleeding properties [21]. Yellow industrial dyes can be extraced from its yellow wood, and its
Corresponding authors. E-mail addresses: [email protected] (X. Zhang), [email protected] (Y. Wang).
https://doi.org/10.1016/j.cplett.2020.137325 Received 18 December 2019; Received in revised form 6 March 2020; Accepted 7 March 2020 Available online 09 March 2020 0009-2614/ © 2020 Elsevier B.V. All rights reserved.
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a few drops of N-methyl-2-pyrrolidone to obtain a black paste, and then coating it onto the working electrode and baked all day in a vacuum at 80 °C. Finally, the working electrode was obtained by pressing at 10 MPa for half a minute. The loaded mass of the active material is between 2.0 and 2.5 mg cm−2. In 1 M H2SO4 electrolyte, the threeelectrode system at 0–1 V voltage range was assembled using working electrode of the platinum mesh loaded with active material, counter electrode of platinum sheet, reference electrodes of saturated calomel electrode. In 6 M KOH electrolyte, the voltage range of the three-electrode system was −1–0 V and the working electrode, auxiliary electrode and reference electrode were nickel foam loaded with active material, Platinum sheet and mercuric/mercuric oxide electrode, respectively. The electrochemical properties of the biochar materials were evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) using CHI660E workstation. A galvanostatic current charge and discharge (GCD) curves were performed using a Xinwei tester. According to Eq. (1), the actual specific capacitance of the electrode material can be calculated. [11,24]:
C= Fig. 1. Simplified diagram of the synthesis process for the porous biochar materials.
I Δt mΔV
(1)
here, I refers to the discharge current, Δt the discharge time, m the mass of active material in the working electrode, and ΔV the total corresponding potential change.
bark and leaves can also be used to extract tanning extracts. It has been reported that the extracts of leaves and flowers of cotinus coggygria own cytotoxicity and antioxidant properties [22]. However, the research on the utilization of its flowers has not been found yet. Therefore, we tried to use it as a biomass material to prepare electrode materials for supercapacitor. In our work, a novel composite activator was explored, which was composed of potassium hydroxide and lithium carbonate. The hierarchical porous biochar was prepared from cotinus coggygria flower in two steps of direct carbonization and chemical activation (Fig. 1) by composite activator. The biochar possesses large specific surface area with hierarchical porous structure. The biochar electrode presents a high specific capacitance in 1 M H2SO4 electrolyte and stable cycling performance in 6 M KOH electrolyte.
3. Results analysis and discussion 3.1. Morphology and structural characterization Fig. 2 reveals FE-SEM images and the element mappings of the biochar. Obviously, the biochar is etched into many holes, in which some carbon, oxygen and a small amount of nitrogen are evenly distributed. The XRD pattern of the biochar is displayed in Fig. 3a, the wider peak at about 22.8° and the sharp peak at 43.9° are indexed as the reflections of (1 2 0) crystal planes of the disordered carbon and (1 1 1) planes of the graphite lattice, separately [23]. The peak at 18.1° is considered as (1 1 0) reflection of C70. As can be seen from the Raman spectrum in Fig. 3b, the two distinct peaks, at 1337 cm−1 and 1589 cm−1, separately represent D band and G band. The peak at 1337 cm−1 refers to the degree of chaos and imperfect structure in the biochar material, and the peak at 1589 cm−1 is related to the vibration of the sp2 hybrid carbon in the graphite crystallite [11,24]. The intensity ratio (ID/IG) of D-band to G-band is an indicator of the degree of graphitization. The ratio of ID/IG is 1.09, demonstrating that the degree of graphitization is not very high. Fig. 3c reveals BET N2 adsorption–desorption isotherms of the biochar. It shows a H4 hysteresis loop after capillary condensation [25,26], which displays a typical characteristic of I + IV isotherm. When the relative pressure p/p0 is close to 0, the curve rises obviously. The
2. Experimental sections The hierarchical porous biochar is prepared as follows, the washed and dried cotinus coggygria flowers were ball milled into powder. The powder was calcined at 600 °C for two hours under N2 protective gas for pre-carbonization. The pre-carbonized biochar was impregnated in the composite activator solution according to the mass ratio 1:3 of the precarbonized biochar to the composite activator. Among them, the composite activator was composed of equal mass of potassium hydroxide and lithium carbonate. The mixture was stirred magnetically for 6 h, followed by dring overnight at 80 °C in an oven, and then was heated to 700 °C for 2 h in N2 protective gas with 5 °C min−1 heating rate, and then naturally droped to 25 °C. The resulted product was acid-washed with 1 M HCl solution for 12 h under magnetic stirring, and then repeatedly washed with impurity-free water, and eventually filtered and evaporated moisture overnight in a vacuum at 80 °C. The sample morphology and elemental analysis were characterized by field-emission scanning electron microscope (FE-SEM) and energydispersive spectrum (EDS). The phase constituents were determined on X-ray diffraction (XRD). Raman spectrum was performed to characterize the graphitization degree of the biochar. The specific surface areas were measured by N2 adsorption–desorption isotherms. The sample was measured using X-ray photoelectron spectrum (XPS). The three-electrode systems were employed to determine the electrochemical properties of the obtained materials. A mixture containing 80 wt% the obtained material, 10 wt% acetylene black and 10 wt% polyvinylidene fluoride was thoroughly ground in an agate mortar with
Fig. 2. (a, b) FESEM images and (c) the corresponding EDS elementary mappings of the biochar. 2
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Fig. 3. (a) XRD pattern, (b) Raman spectra, (c) N2 adsorption–desorption isotherm, and (d) pores size distribution curve.
Fig. 4. (a) X-ray photoelectron spectra, high-resolution (b) C 1s, (c) N 1s, and (d) O 1s spectra of the biochar.
3
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Fig. 5. In 1 M H2SO4 electrolyte, (a) CV plots, (b) GCD curves, (c) Graph of specific capacitance as a function of current density, and (d) EIS spectra of the biochar electrode. Table 1 A comparison of specific capacitances of porous carbons derived from various biomass sources. Biomass
Activator
Capacitance (F g−1)
Current density (A g−1)
Electrolyte
Ref.
Willow catkins Phoenix seeds Corn straw
KOH KOH KOH KOH KOH KOH KOH + Li2CO3
1 0.5 0.2 0.3 − − 1 mA cm−2 0.5 0.5
6 2 6 1 1 6 6 1 6
[13] [14] [29]
Coffee endocarp Waste paper Lignocellulosic Cotinus coggygria flowers
292 376 327 259 176 180 161 413 279
M M M M M M M M M
KOH H2SO4 KOH H2SO4 H2SO4 KOH KOH H2SO4 KOH
[37] [38] [39] This work
provides a low resistance channel for ion and electron transport by shortening the transport distance [29]. The presence of abundant micropores facilitates charge storage at the electrode and electrolyte interfaces [25,30,31]. This multi-stage channel provides a fast transport path for electrolyte ions. The prevailing view of the mechanisms for KOH activation is that between 400 °C and 600 °C, the redox reaction between carbon precursor and molten KOH starts and forms K2CO3, resulting in abundant micro/mesopores. When the temperature reaches 600 °C, the generated K2CO3 decomposes to produce CO2. The water vapor and CO2 can vaporize carbon atoms and further increase the porosity of porous materials [32], which is a physical activation process. As the temperature exceeds 700 °C, potassium compounds (K2CO3, K2O) are reduced by carbon to generate elemental potassium vapor, which can be effectively inserted into the carbon layer and cause the carbon layer to expand, leading to a highly porous structure [13,14].
material adsorbs a large amount of nitrogen, suggesting the existence of a large amount of micropores in the biochar [20,27]. In the region where the relative pressure p/p0 is 0.02–0.97, the curve rises more gently, approximately reaching the horizontal platform, and a hysteresis loop occurs when the p/p0 of 0.45–0.85, implying the formation of mesopores within the biochar. The curve turned upwards in the range of p/p0 of 0.97–1, which denotes the presence of macropores within the biochar. As exhibited in Fig. 3d, the biochar possesses BET surface area of 959.04 cm2 g−1, including micropore surface area of 735.64 cm2 g−1. Total pore volume and micropore volume are 0.42 cm3 g−1 and 0.28 cm3 g−1, respectively. The average pore size is 1.73 nm. These results show that the biochar contains a large number of micropores and a certain amount of mesopores, in addition to a few large holes. A small number of large pores provide sufficient space to buffer the ions, making them more accessible to the inner surface of the active substance [28]. At the same time, an appropriate amount of mesopores 4
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Fig. 6. In 6 M KOH electrolyte, (a) CV plots, (b) GCD curves, (c) Graph of specific capacitance as a function of current density, (d) EIS spectra and (e) long cycle performance of the biochar electrode.
However, there was less research on the mechanism of carbonate activation. Some researchers had proposed that the reaction mechanism of potassium carbonate was as the reports in the Refs. [33,34]: when the temperature exceeds 800 °C, K2CO3 becomes oxidized by carbon to CO and forms the element K in vapor. It is well known that the melting point of lithium carbonate (723 °C) is lower than that of potassium carbonate (891 °C). In our work, lithium carbonate and potassium hydroxide synergistically reduce the activation energy of the reaction during the activation process. It is deduced that when the activation temperature is below 600 °C, the carbon material fully impregnated with the activator reacts with potassium hydroxide. In the process of heating to 700 °C, lithium carbonate and the produced potassium carbonate are decomposed to produce CO2, and the compounds of Li and K (Li2O, Li2CO3, K2O and K2CO3) are reduced by carbon to produce CO [34], resulting in a large amount of micropores. With the etching of alkaline substances (Li2CO3
and K2CO3), some micropores are transformed into mesopores. In addition, some lithium carbonate may begin to melt and damage the carbon skeleton, forming some large pores, and no large-scale collapse occurred. Post-activation washing of the biochar is generally required to remove residual alkaline substances and other inorganic residue. The activation process of complex activators is more complicated, and its mechanism needs to be further studied. The surface functional groups of the biochar have a certain influence on the electrochemical properties. The XPS analysis of the biochar is carried out here (Fig. 4). As shown in Fig. 4a, it has three key peaks, C1s (280.8 eV), weak N1s (395.7 eV) and O1s (529.1 eV) and C, N and O contents are about 87.5 at%, 0.3 at% and 12.1 at%, respectively. The C1s spectra (Fig. 4b) exhibits four peaks, consisting two stronger peaks sp2-bonded carbon (284.4 eV) and sp3-bonded carbon (285.5 eV) in aromatic rings, and the other two weaker peaks CeO (286.9 eV, epoxy and alkoxy) and C]O (289.2 eV, carbonyl) [29,35]. Fig. 4c shows the 5
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coggygria flower in two steps of direct carbonization and chemical activation by composite activator. The biochar possesses high BET surface-area with hierarchical porous structure. The biochar performs excellent specific capacitance in acid electrolyte at 0.5 A g−1 and superior cycle stability in alkaline electrolyte at 5 A g−1. The hierarchical porous biochar exhibits some advantages such as easy to prepare, low in price and excellent in performance. It is expected to become a new breakthrough point in the choice of activator for the synthesis of highefficiency biochar materials and is also expected to be widely used as an electrode material for supercapacitors.
N1s peak which can be divided into two peaks such as pyrrole nitrogen (400.1 eV) and pyridine-N-oxide (403.1 eV) [36]. The type of nitrogen has a significant effect on electrochemical performance, such as pyrrole nitrogen contributing to pseudo-capacitance [11]. There are also two mutation peaks centered at 532.7 eV and 534.0 eV in the O1s spectrum (Fig. 4b), corresponding to two types of oxygen functional group, namely C]O and OeC]O bonds, which contribute to increased redox capacitance and wettability [26]. 3.2. Electrochemical performance evaluation
CRediT authorship contribution statement
In 1 M H2SO4 electrolyte, CV curves (Fig. 5a) are all approximately rectangular. We can observe the presences of the slight humps near 0.4 V, which may be caused by electrochemically active functional groups [7]. Considering the low nitrogen content in the biochar, the humps may be mainly attributed to the pseudo-capacitance reaction by the oxygen-containing group [29]. Fig. 5b shows GCD curves, it can be seen that all the curves at 1–5 A g−1 current densities are almost linear and symmetrical, indicating an electric double-layer capacitance with good reversibility. In addition, at 0.5 A g−1, the GCD curves are asymmetrical, which may be attributed to pseudo-capacitance. The supercapacitor (Fig. 5c) delivers the high specific capacitance of 413.5 F g−1 at 0.5 A g−1 and 254.8 F g−1 when the current density reaches 5 A g−1, respectively. Electrochemical performance of this work was compared with porous carbons derived from various biomass sources (Table 1). It can be clearly seen that 413.5 F g−1 specific capacitance at 0.5 A g−1 in our work under acidic electrolyte is much higher than that of corn straw biochar (259 F g−1 at 0.3 A g−1) [29] and coffee endocarp biochar (176 F g−1) [37]. EIS spectra of the biochar electrode is drawn in Fig. 5d. The intercept of the horizontal axis reflects the inner resistance Rs, representing the inherent resistance of the electrode and electrolyte, and the contact resistance of the platinum mesh and the material [40]. The inner resistance Rs is 1.275 Ω, which is small, indicating that the biochar electrode has good electrical conductivity. When the frequency is high, the graphic is a semicircle, which refers to the charge transfer resistance (Rct) [41], low Rct (0.113 Ω) means good electrical conductivity and well wettability, which results in a high specific capacitance. When the frequency is low, the line is nearly 90°, representing the idealized capacitance. In 6 M KOH electrolyte, as can be seen from Fig. 6a, the enclosed pattern is approximately rectangular, and an inconspicuous hump near −0.8 V was observed in all the CV curves, which may be due to pseudocapacitance [42,43]. The reversibility of the biochar electrode is represented by the symmetry line of Fig. 6b. As shown in Fig. 6c, when the current density rises from 0.5 to 5 A g−1, the specific capacitance of the biochar material slightly decreases from 285.9 to 259.9 F g−1, indicating a superior rate performance of the biochar electrode in alkaline electrolyte. EIS spectra of the biochar electrode is revealed in Fig. 6d. The intercept of the horizontal axis reflects the inner resistance Rs is 0.82 Ω, which are small, indicating that the biochar electrode has good electrical conductivity. The Rct is 0.126 Ω, low Rct means high electrical conductivity and good wettability [44]. When the frequency is low, the line is close to 90°, which denotes the idealized capacitance behaviour of the biochar material. As can be seen from Fig. 6e, after 36,000 cycles at 5 A g−1, the biochar electrode exhibits a high reversible capacitance 279.9 F g−1, suggesting superior cycling stability of the biochar electrode. The increased specific capacitance after 36,000 cycles may be thanks to the multi-stage pore structure, and electrolyte ions are more easily reached on the surface of the active material. Furthermore, multiple charge and discharge causes the electrode material to be fully infiltrated and more active sites are excited [45–47].
Yanhong Li: Investigation, Data curation, Writing - original draft. Xin Zhang: Writing - review & editing. Jiaying Deng: Investigation. Xiaheng Yang: Resources. Jinlong Wang: Data curation. Yanzhi Wang: Conceptualization, Project administration. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. References [1] Y.H. Cao, K.L. Wang, X.M. Wang, Z.R. Gu, Q.H. Fan, W. Gibbons, J.D. Hoefelmeyer, P.R. Kharel, M. Shrestha, Electrochim. Acta 212 (2016) 839–847, https://doi.org/ 10.1016/j.electacta.2016.07.069. [2] B. Kirubasankar, V. Murugadoss, J. Lin, T. Ding, M. Dong, H. Liu, J. Zhang, T.X. Li, N. Wang, Z.H. Guo, S. Angaiah, Nanoscale. 10 (2018) 20414–20425, https://doi. org/10.1039/c8nr06345a. [3] S.E.M. Pourhosseinia, O. Norouzia, H.R. Naderi, Biomass Bioenergy 107 (2017) 287–298, https://doi.org/10.1016/j.biombioe.2017.10.025. [4] N.F. He, S. Yoo, J.J. Meng, O. Yildiz, P.D. Bradford, S. Park, W. Gao, Carbon. 120 (2017) 304–312, https://doi.org/10.1016/j.carbon.2017.05.056. [5] X.F. Tan, S.B. Liu, Y.G. Liu, Y.L. Gu, G.M. Zeng, X.J. Hu, X. Wang, S.H. Liu, L.H. Jiang, Bioresour. Technol. 227 (2017) 359–372, https://doi.org/10.1016/j. biortech.2016.12.083. [6] J. Pallarés, A. González-Cencerrado, I. Arauzo, Biomass Bioenergy 115 (2018) 64–73, https://doi.org/10.1016/j.biombioe.2018.04.015. [7] K. Wang, N. Zhao, S.W. Lei, R. Yan, X.D. Tian, J.Z. Wang, Y. Song, D.F. Xu, Q.G. Guo, L. Liu, Electrochim. Acta 166 (2015) 1–11, https://doi.org/10.1016/j. electacta.2015.03.048. [8] A.M. Dehkhoda, E. Gyenge, N. Ellis, Biomass Bioenergy 87 (2016) 107–121, https://doi.org/10.1016/j.biombioe.2016.02.023. [9] Md. AzharulIslam, M.J. Ahmed, W.A. Khanday, M. Asif, B.H. Hameed, Ecotoxicol. Environ. Saf. 138 (2017) 279–285, https://doi.org/10.1016/j.ecoenv.2017.01.010. [10] X. Du, W. Zhao, Y. Wang, C.Y. Wang, M.M. Chen, T. Qi, C. Hua, M.G. Ma, Bioresour. Technol. 149 (2013) 31–37, https://doi.org/10.1016/j.biortech.2013.09.026. [11] Y.H. Cao, X.M. Wang, Z.G. Gua, Q.H. Fan, W. Gibbons, V. Gadhamshettyd, N. Aie, G.N. Zeng, J. Power Sources 384 (2018) 360–366, https://doi.org/10.1016/j. jpowsour.2018.02.079. [12] M. Myglovets, O.I. Poddubnaya, O. Sevastyanova, M.E. Lindstrom, B. Gawdzik, M. Sobiesiak, M.M. Tsyba, V.I. Sapsay, D.O. Klymchuk, A.M. Puziy, Carbon 80 (2014) 771–783, https://doi.org/10.1016/j.carbon.2014.09.032. [13] Dr. Y. Shen, T.T Qu, K. Xiang, Y. Zhang, Prof. Z.F Tian, Prof. M.J. Xie, Prof. X.F. Gu, Chem. Select. 2 (2017) 10704−10708. https://doi.org/10.1002/slct.201702050. [14] L.J. Xie, G.H. Sun, F.Y. Su, X.Q. Guo, Q.Q. Kong, X.M. Li, X.H. Huang, L. Wan, W. song, K.X. Li, C.X. Lv, C.M. Chen, J. Mater. Chem. A. 4 (2016) 1637−1646. https:// doi.org/10.1039/C5TA09043A. [15] K.R. Thines, E.C. Abdullah, N.M. Mubarak, M. Ruthiraan, Renew. Sustain. Energy Rev. 67 (2017) 257–276, https://doi.org/10.1016/j.rser.2016.09.057. [16] G.J. Yang, S.J. Park, J. Alloy. Compd. 741 (2018) 360–367, https://doi.org/10. 1016/j.jallcom.2018.01.108. [17] J. Ding, H.L. Wang, Z. Li, K. Cui, D. Karpuzov, X.H. Tan, A. Kohandehghanab, D. Mitlin, Energy Environ. Sci. 8 (2015) 941–955, https://doi.org/10.1039/ c4ee02986k. [18] J.M. Jung, J.I. Oh, K. Baek, J. Lee, E.E. Kwon, Energy Convers. Manage. 165 (2018) 628–633, https://doi.org/10.1016/j.enconman.2018.03.096. [19] D. Pontirolia, S. Scaravonati, G. Magnani, L. Fornasini, D. Bersani, G. Bertoni,
4. Conclusions The hierarchical porous biochar was prepared from cotinus 6
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Y. Li, et al.
[20] [21] [22]
[23] [24] [25] [26] [27] [28] [29]
[30] [31] [32]
[33]
10.15376/biores.12.2.3340-3350. [34] J. Hayashi, T. Horikawa, I. Takeda, K. Muroyama, F.N. Ani, Carbon 40 (2002) 2381–2386. [35] X.H. Zhang, K. Zhang, H.X. Li, Q. Wang, L. Jin, Q. Cao, J. Appl. Electrochem. 48 (2018) 415–426, https://doi.org/10.1007/s10800-018-1170-x. [36] X.L. Su, M.Y. Cheng, L. Fu, J.H. Yang, X.C. Zheng, X.X. Guan, J. Power Sources 362 (2017) 27–38, https://doi.org/10.1016/j.jpowsour.2017.07.021. [37] J.M. Nabais, J.G. Teixeira, I. Almeida, Bioresour. Technol. 102 (2011) 2781–2787, https://doi.org/10.1016/j.biortech.2010.11.083. [38] D. Kalpana, S. Cho, S. Lee, Y. Lee, R. Misra, N. Renganathan, J. Power Sources 190 (2009) 587–591, https://doi.org/10.1016/j.jpowsour.2009.01.058. [39] P. González-García, T.A. Centeno, E. Urones-Garrote, D. Ávila-Brande, L.C. OteroDíaz, Appl. Surf. Sci. 265 (2013) 731–737, https://doi.org/10.1016/j.apsusc.2012. 11.092. [40] C. Liang, J.P. Bao, C.G. Li, H. Huang, C.L. Chen, Y. Lou, H.Y. Lu, H.B. Lin, Z. Shi, S.H. Feng, Micropor. Mesopor. Mater. 251 (2017) 77–82, https://doi.org/10.1016/ j.micromeso.2017.05.044. [41] J.W. Qi, W.D. Zhang, L. Xu, Chem. Eur. J. 24 (2018) 18097–18105, https://doi.org/ 10.1002/chem.201804302. [42] K.S. Xia, Q.M. Gao, J.H. Jiang, J. Hu, Carbon 46 (2008) 1718–1726, https://doi. org/10.1016/j.carbon.2008.07.018. [43] P. Abudu, L.X. Wang, M.J. Xu, D.Z. Jia, X.C. Wang, L.X. Jia, Chem. Phys. Lett. 702 (2018) 1–7, https://doi.org/10.1016/j.cplett.2018.04.055. [44] M. Genovese, H. Wu, A. Virya, J. Li, P.Z. Shen, K. Lian, Electrochim. Acta 273 (2018) 392–401, https://doi.org/10.1016/j.electacta.2018.04.061. [45] O.Y. Yu, R.J. Huang, X.F. Xia, H.T. Ye, X.Y. Jiao, L. Wang, W. Lei, Q.L. Hao, Chem. Eng. J. 355 (2019) 416–427, https://doi.org/10.1016/j.cej.2018.08.142. [46] D.Y. Lei, K.H. Song, X.D. Li, H.Y. Kim, B.S. Kim, J. Mater. Sci. 52 (2017) 2158–2168, https://doi.org/10.1007/s10853-016-0504-5. [47] P.Z. Wang, W.X. Luo, N.N. Guo, L.X. Wang, D.Z. Jia, Z.B. Zhao, S. Zhang, M.J. Xu, Chem. Phys. Lett. 730 (2019) 32–38, https://doi.org/10.1016/j.cplett.2019.05. 032.
C. Milanese, A. Girella, F. Ridi, R. Verucchi, L. Mantovani, A. Malcevschi, M. Riccò, Microporous Mesoporous Mater. 285 (2019) 161–169, https://doi.org/10.1016/j. micromeso.2019.05.002. Y.H. Fu, N.Y. Zhang, Y.F. Shen, X.L. Ge, M.D. Chen, Bioresour. Technol. 269 (2018) 67–73, https://doi.org/10.1016/j.biortech.2018.08.083. M. Marc̆etić, D. Boz̆ić, M. Milenković, N. Males̆ević, Sinis̆a Radulović, N. Kovac̆ević, Phytother. Res. 27 (2013) 1658–1663. https://doi.org/10.1002/ptr.4919. ̆ K. Savikina, G. Zdunić, T. Janković, T. Stanojković, Z. Juranić, Nebojs̆a Menković, Nat. Prod. Res. 18 (2009) 1731−1739. https://doi.org/10.1080/ 14786410802267650. X.L. Su, S. Jiang, G.P. Zheng, X.C. Zheng, J.H. Yang, Z.Y. Liu, J. Mater. Sci. 53 (2018) 9191–9205, https://doi.org/10.1007/s10853-018-2208-5. A.M. Dehkhoda, N. Ellis, E. Gyenge, Micropor. Mesopor. Mater. 224 (2016) 217–228, https://doi.org/10.1016/j.micromeso.2015.11.041. K. Wang, Y. Song, R. Yan, N. Zhao, X.D. Tian, X. Li, Q.G. Guo, Z.J. Liu, Appl. Surf. Sci. 394 (2017) 569–577, https://doi.org/10.1016/j.apsusc.2016.10.161. X.L. Su, S.H. Li, S. Jiang, Z.K. Peng, X.X. Guan, X.C. Zheng, Adv. Powder Technol. 29 (2018) 2097–2107, https://doi.org/10.1016/j.apt.2018.05.018. M. Genovese, K. Lian, J. Mater. Chem. A 5 (2017) 3939–3947, https://doi.org/10. 1039/c6ta10382k. Y.Y. Liu, G.X. Dai, L.J. Zhu, S.R. Wang, ChemElectroChem. 13 (2018) 287–288, https://doi.org/10.1002/celc.201801272. Z.P. Qiu, Y.S. Wang, X. Bi, T. Zhou, J. Zhou, J.P. Zhao, Z.C. Miao, W.M. Yi, P. Fu, S.P. Zhuo, J. Power Sources 376 (2018) 82–90, https://doi.org/10.1016/j. jpowsour.2017.11.077. S. Yang, S.L. Wang, X. Liu, L. Li, Carbon 147 (2019) 540–549, https://doi.org/10. 1016/j.carbon.2019.03.023. A.G. Pandolfo, A.F. Hollenkamp, J. Power Sources. 157 (2006) 11–27. https:// doi. org/10.1016/j.jpowsour.2006.02.065. S. Zhang, C.L. Wu, W. Wu, C. Zhou, Z.W. Xi, Y.Y. Deng, X. Wang, P. Quan, X.J. Li, Y.F. Luo, J. Power Sources 424 (2019) 1–7, https://doi.org/10.1016/j.jpowsour. 2019.03.100. X.F. Li, W.T. Chen, L.Q. Dou, BioResources 12 (2017) 3340–3350, https://doi.org/
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Research paper
Hierarchical porous biochar derived from cotinus coggygria flower by using a novel composite activator for supercapacitors ⁎
Yanhong Lia, Xin Zhangb, , Jiaying Denga, Xiaheng Yanga, Jinlong Wanga, Yanzhi Wanga,
T
⁎
a Hebei Key Laboratory of Applied Chemistry, Hebei Key Laboratory of Heavy Metal Deep-remediation in Water and Resource Reuse, School of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao, Hebei 066004, China b Hubei Key Laboratory of Low Dimensional Optoelectronic Materials and Devices, Hubei University of Arts and Science, Xiangyang 441053, China
H I GH L IG H T S
hierarchical porous biochar has been prepared from cotinus coggygria flower. • The composite activator has been developed to synthesize the biochar. • AThenovel delivers the high specific capacitance in 1 M H2SO4 electrolyte. • The biochar • biochar exhibits the stable cycling performance in 6 M KOH electrolyte.
A R T I C LE I N FO
A B S T R A C T
Keywords: Energy storage and conversion Biomaterials Hierarchical porous Cotinus coggygria flowers Composite activator
Hierarchical porous biochar with large BET surface area of 959.04 cm2 g−1 was synthesized by using a novel composite activator from cotinus coggygria flowers. The biochar delivers excellent specific capacitance of 413.5 F g−1 at current density of 0.5 A g−1 in 1 M H2SO4 electrolyte and a well reversible capacitance of 279.9 F g−1 at current density of 5 A g−1 in 6 M KOH electrolyte after 36,000 cycles. The excellent specific capacitance and the stable cycling performance benefit from the synergism of the composite activator. This provides a meaningful reference for the synthesis of supercapacitor biomaterials.
1. Introduction In recent years, a growing number of research workers are jioning the rush to research supercapacitors. Compared with batteries, supercapacitors possess high power density, superior cycling performance and short charging time [1]. Biochar materials are promising become electrode materials for supercapacitors because of their low costs, good safeties and high electrical conductivities [2–4]. The methods for preparing such materials include direct carbonization method, hydrothermal method, and activation method. Activation methods are classified into physical activation and chemical activation [5,6]. KOH [7,8], NaOH [9], ZnCl2 [10], KCl [11], HNO3 [3] and H3PO4 [12] are commonly used as chemical activation reagents. Many researchers have a higher evaluation of KOH because electrode materials prepared with KOH as an activator tend to have higher specific capacitance. For instance, Yu et al. [13] reported a porous carbon material derived from phoenix seeds, which showed 376 F g−1 specific capacitance in 2 M H2SO4 aqueous solution at 0.5 A g−1. Xie et al. [14] fabricated a porous carbon microtube by willow catkins with activation of KOH, which ⁎
presented 292 F g−1 specific capacitance at 1 A g−1. Although KOHactivated biomass carbon delivers a high specific capacity, KOH acts as a base and inevitably pollutes the environment during post-treatment. It is well known that biomass as a carbon source has been widely used in the study of electrode materials. Biomass is a low-cost, renewable raw material, which can be turned into a treasure after a series of experimental treatments [3]. Biochar is an emerging carbon material formed from biomass raw materials through a series of processes [15]. Meanwhile, biochar has the advantages of high specific surface area, abundant pores, and well electrical conductivity [4]. Many biomass have been used to make biomass charcoal, such as fruit peels [16], peanut shell [17], walnut shell [11], barley straw [6], animal waste [18,19], rice husk [20], and so on. Cotinus coggygria, normally known as the “Smoke Tree”, is distributed in southern Europe, central Asia, from the Himalaya to northern China. Wild cotinus coggygria is a resource plant with great utilization value. Cotinus coggygria is widely used in medicine due to its antibacterial, anti-inflammatory and anti-bleeding properties [21]. Yellow industrial dyes can be extraced from its yellow wood, and its
Corresponding authors. E-mail addresses: [email protected] (X. Zhang), [email protected] (Y. Wang).
https://doi.org/10.1016/j.cplett.2020.137325 Received 18 December 2019; Received in revised form 6 March 2020; Accepted 7 March 2020 Available online 09 March 2020 0009-2614/ © 2020 Elsevier B.V. All rights reserved.
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a few drops of N-methyl-2-pyrrolidone to obtain a black paste, and then coating it onto the working electrode and baked all day in a vacuum at 80 °C. Finally, the working electrode was obtained by pressing at 10 MPa for half a minute. The loaded mass of the active material is between 2.0 and 2.5 mg cm−2. In 1 M H2SO4 electrolyte, the threeelectrode system at 0–1 V voltage range was assembled using working electrode of the platinum mesh loaded with active material, counter electrode of platinum sheet, reference electrodes of saturated calomel electrode. In 6 M KOH electrolyte, the voltage range of the three-electrode system was −1–0 V and the working electrode, auxiliary electrode and reference electrode were nickel foam loaded with active material, Platinum sheet and mercuric/mercuric oxide electrode, respectively. The electrochemical properties of the biochar materials were evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) using CHI660E workstation. A galvanostatic current charge and discharge (GCD) curves were performed using a Xinwei tester. According to Eq. (1), the actual specific capacitance of the electrode material can be calculated. [11,24]:
C= Fig. 1. Simplified diagram of the synthesis process for the porous biochar materials.
I Δt mΔV
(1)
here, I refers to the discharge current, Δt the discharge time, m the mass of active material in the working electrode, and ΔV the total corresponding potential change.
bark and leaves can also be used to extract tanning extracts. It has been reported that the extracts of leaves and flowers of cotinus coggygria own cytotoxicity and antioxidant properties [22]. However, the research on the utilization of its flowers has not been found yet. Therefore, we tried to use it as a biomass material to prepare electrode materials for supercapacitor. In our work, a novel composite activator was explored, which was composed of potassium hydroxide and lithium carbonate. The hierarchical porous biochar was prepared from cotinus coggygria flower in two steps of direct carbonization and chemical activation (Fig. 1) by composite activator. The biochar possesses large specific surface area with hierarchical porous structure. The biochar electrode presents a high specific capacitance in 1 M H2SO4 electrolyte and stable cycling performance in 6 M KOH electrolyte.
3. Results analysis and discussion 3.1. Morphology and structural characterization Fig. 2 reveals FE-SEM images and the element mappings of the biochar. Obviously, the biochar is etched into many holes, in which some carbon, oxygen and a small amount of nitrogen are evenly distributed. The XRD pattern of the biochar is displayed in Fig. 3a, the wider peak at about 22.8° and the sharp peak at 43.9° are indexed as the reflections of (1 2 0) crystal planes of the disordered carbon and (1 1 1) planes of the graphite lattice, separately [23]. The peak at 18.1° is considered as (1 1 0) reflection of C70. As can be seen from the Raman spectrum in Fig. 3b, the two distinct peaks, at 1337 cm−1 and 1589 cm−1, separately represent D band and G band. The peak at 1337 cm−1 refers to the degree of chaos and imperfect structure in the biochar material, and the peak at 1589 cm−1 is related to the vibration of the sp2 hybrid carbon in the graphite crystallite [11,24]. The intensity ratio (ID/IG) of D-band to G-band is an indicator of the degree of graphitization. The ratio of ID/IG is 1.09, demonstrating that the degree of graphitization is not very high. Fig. 3c reveals BET N2 adsorption–desorption isotherms of the biochar. It shows a H4 hysteresis loop after capillary condensation [25,26], which displays a typical characteristic of I + IV isotherm. When the relative pressure p/p0 is close to 0, the curve rises obviously. The
2. Experimental sections The hierarchical porous biochar is prepared as follows, the washed and dried cotinus coggygria flowers were ball milled into powder. The powder was calcined at 600 °C for two hours under N2 protective gas for pre-carbonization. The pre-carbonized biochar was impregnated in the composite activator solution according to the mass ratio 1:3 of the precarbonized biochar to the composite activator. Among them, the composite activator was composed of equal mass of potassium hydroxide and lithium carbonate. The mixture was stirred magnetically for 6 h, followed by dring overnight at 80 °C in an oven, and then was heated to 700 °C for 2 h in N2 protective gas with 5 °C min−1 heating rate, and then naturally droped to 25 °C. The resulted product was acid-washed with 1 M HCl solution for 12 h under magnetic stirring, and then repeatedly washed with impurity-free water, and eventually filtered and evaporated moisture overnight in a vacuum at 80 °C. The sample morphology and elemental analysis were characterized by field-emission scanning electron microscope (FE-SEM) and energydispersive spectrum (EDS). The phase constituents were determined on X-ray diffraction (XRD). Raman spectrum was performed to characterize the graphitization degree of the biochar. The specific surface areas were measured by N2 adsorption–desorption isotherms. The sample was measured using X-ray photoelectron spectrum (XPS). The three-electrode systems were employed to determine the electrochemical properties of the obtained materials. A mixture containing 80 wt% the obtained material, 10 wt% acetylene black and 10 wt% polyvinylidene fluoride was thoroughly ground in an agate mortar with
Fig. 2. (a, b) FESEM images and (c) the corresponding EDS elementary mappings of the biochar. 2
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Fig. 3. (a) XRD pattern, (b) Raman spectra, (c) N2 adsorption–desorption isotherm, and (d) pores size distribution curve.
Fig. 4. (a) X-ray photoelectron spectra, high-resolution (b) C 1s, (c) N 1s, and (d) O 1s spectra of the biochar.
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Fig. 5. In 1 M H2SO4 electrolyte, (a) CV plots, (b) GCD curves, (c) Graph of specific capacitance as a function of current density, and (d) EIS spectra of the biochar electrode. Table 1 A comparison of specific capacitances of porous carbons derived from various biomass sources. Biomass
Activator
Capacitance (F g−1)
Current density (A g−1)
Electrolyte
Ref.
Willow catkins Phoenix seeds Corn straw
KOH KOH KOH KOH KOH KOH KOH + Li2CO3
1 0.5 0.2 0.3 − − 1 mA cm−2 0.5 0.5
6 2 6 1 1 6 6 1 6
[13] [14] [29]
Coffee endocarp Waste paper Lignocellulosic Cotinus coggygria flowers
292 376 327 259 176 180 161 413 279
M M M M M M M M M
KOH H2SO4 KOH H2SO4 H2SO4 KOH KOH H2SO4 KOH
[37] [38] [39] This work
provides a low resistance channel for ion and electron transport by shortening the transport distance [29]. The presence of abundant micropores facilitates charge storage at the electrode and electrolyte interfaces [25,30,31]. This multi-stage channel provides a fast transport path for electrolyte ions. The prevailing view of the mechanisms for KOH activation is that between 400 °C and 600 °C, the redox reaction between carbon precursor and molten KOH starts and forms K2CO3, resulting in abundant micro/mesopores. When the temperature reaches 600 °C, the generated K2CO3 decomposes to produce CO2. The water vapor and CO2 can vaporize carbon atoms and further increase the porosity of porous materials [32], which is a physical activation process. As the temperature exceeds 700 °C, potassium compounds (K2CO3, K2O) are reduced by carbon to generate elemental potassium vapor, which can be effectively inserted into the carbon layer and cause the carbon layer to expand, leading to a highly porous structure [13,14].
material adsorbs a large amount of nitrogen, suggesting the existence of a large amount of micropores in the biochar [20,27]. In the region where the relative pressure p/p0 is 0.02–0.97, the curve rises more gently, approximately reaching the horizontal platform, and a hysteresis loop occurs when the p/p0 of 0.45–0.85, implying the formation of mesopores within the biochar. The curve turned upwards in the range of p/p0 of 0.97–1, which denotes the presence of macropores within the biochar. As exhibited in Fig. 3d, the biochar possesses BET surface area of 959.04 cm2 g−1, including micropore surface area of 735.64 cm2 g−1. Total pore volume and micropore volume are 0.42 cm3 g−1 and 0.28 cm3 g−1, respectively. The average pore size is 1.73 nm. These results show that the biochar contains a large number of micropores and a certain amount of mesopores, in addition to a few large holes. A small number of large pores provide sufficient space to buffer the ions, making them more accessible to the inner surface of the active substance [28]. At the same time, an appropriate amount of mesopores 4
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Fig. 6. In 6 M KOH electrolyte, (a) CV plots, (b) GCD curves, (c) Graph of specific capacitance as a function of current density, (d) EIS spectra and (e) long cycle performance of the biochar electrode.
However, there was less research on the mechanism of carbonate activation. Some researchers had proposed that the reaction mechanism of potassium carbonate was as the reports in the Refs. [33,34]: when the temperature exceeds 800 °C, K2CO3 becomes oxidized by carbon to CO and forms the element K in vapor. It is well known that the melting point of lithium carbonate (723 °C) is lower than that of potassium carbonate (891 °C). In our work, lithium carbonate and potassium hydroxide synergistically reduce the activation energy of the reaction during the activation process. It is deduced that when the activation temperature is below 600 °C, the carbon material fully impregnated with the activator reacts with potassium hydroxide. In the process of heating to 700 °C, lithium carbonate and the produced potassium carbonate are decomposed to produce CO2, and the compounds of Li and K (Li2O, Li2CO3, K2O and K2CO3) are reduced by carbon to produce CO [34], resulting in a large amount of micropores. With the etching of alkaline substances (Li2CO3
and K2CO3), some micropores are transformed into mesopores. In addition, some lithium carbonate may begin to melt and damage the carbon skeleton, forming some large pores, and no large-scale collapse occurred. Post-activation washing of the biochar is generally required to remove residual alkaline substances and other inorganic residue. The activation process of complex activators is more complicated, and its mechanism needs to be further studied. The surface functional groups of the biochar have a certain influence on the electrochemical properties. The XPS analysis of the biochar is carried out here (Fig. 4). As shown in Fig. 4a, it has three key peaks, C1s (280.8 eV), weak N1s (395.7 eV) and O1s (529.1 eV) and C, N and O contents are about 87.5 at%, 0.3 at% and 12.1 at%, respectively. The C1s spectra (Fig. 4b) exhibits four peaks, consisting two stronger peaks sp2-bonded carbon (284.4 eV) and sp3-bonded carbon (285.5 eV) in aromatic rings, and the other two weaker peaks CeO (286.9 eV, epoxy and alkoxy) and C]O (289.2 eV, carbonyl) [29,35]. Fig. 4c shows the 5
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coggygria flower in two steps of direct carbonization and chemical activation by composite activator. The biochar possesses high BET surface-area with hierarchical porous structure. The biochar performs excellent specific capacitance in acid electrolyte at 0.5 A g−1 and superior cycle stability in alkaline electrolyte at 5 A g−1. The hierarchical porous biochar exhibits some advantages such as easy to prepare, low in price and excellent in performance. It is expected to become a new breakthrough point in the choice of activator for the synthesis of highefficiency biochar materials and is also expected to be widely used as an electrode material for supercapacitors.
N1s peak which can be divided into two peaks such as pyrrole nitrogen (400.1 eV) and pyridine-N-oxide (403.1 eV) [36]. The type of nitrogen has a significant effect on electrochemical performance, such as pyrrole nitrogen contributing to pseudo-capacitance [11]. There are also two mutation peaks centered at 532.7 eV and 534.0 eV in the O1s spectrum (Fig. 4b), corresponding to two types of oxygen functional group, namely C]O and OeC]O bonds, which contribute to increased redox capacitance and wettability [26]. 3.2. Electrochemical performance evaluation
CRediT authorship contribution statement
In 1 M H2SO4 electrolyte, CV curves (Fig. 5a) are all approximately rectangular. We can observe the presences of the slight humps near 0.4 V, which may be caused by electrochemically active functional groups [7]. Considering the low nitrogen content in the biochar, the humps may be mainly attributed to the pseudo-capacitance reaction by the oxygen-containing group [29]. Fig. 5b shows GCD curves, it can be seen that all the curves at 1–5 A g−1 current densities are almost linear and symmetrical, indicating an electric double-layer capacitance with good reversibility. In addition, at 0.5 A g−1, the GCD curves are asymmetrical, which may be attributed to pseudo-capacitance. The supercapacitor (Fig. 5c) delivers the high specific capacitance of 413.5 F g−1 at 0.5 A g−1 and 254.8 F g−1 when the current density reaches 5 A g−1, respectively. Electrochemical performance of this work was compared with porous carbons derived from various biomass sources (Table 1). It can be clearly seen that 413.5 F g−1 specific capacitance at 0.5 A g−1 in our work under acidic electrolyte is much higher than that of corn straw biochar (259 F g−1 at 0.3 A g−1) [29] and coffee endocarp biochar (176 F g−1) [37]. EIS spectra of the biochar electrode is drawn in Fig. 5d. The intercept of the horizontal axis reflects the inner resistance Rs, representing the inherent resistance of the electrode and electrolyte, and the contact resistance of the platinum mesh and the material [40]. The inner resistance Rs is 1.275 Ω, which is small, indicating that the biochar electrode has good electrical conductivity. When the frequency is high, the graphic is a semicircle, which refers to the charge transfer resistance (Rct) [41], low Rct (0.113 Ω) means good electrical conductivity and well wettability, which results in a high specific capacitance. When the frequency is low, the line is nearly 90°, representing the idealized capacitance. In 6 M KOH electrolyte, as can be seen from Fig. 6a, the enclosed pattern is approximately rectangular, and an inconspicuous hump near −0.8 V was observed in all the CV curves, which may be due to pseudocapacitance [42,43]. The reversibility of the biochar electrode is represented by the symmetry line of Fig. 6b. As shown in Fig. 6c, when the current density rises from 0.5 to 5 A g−1, the specific capacitance of the biochar material slightly decreases from 285.9 to 259.9 F g−1, indicating a superior rate performance of the biochar electrode in alkaline electrolyte. EIS spectra of the biochar electrode is revealed in Fig. 6d. The intercept of the horizontal axis reflects the inner resistance Rs is 0.82 Ω, which are small, indicating that the biochar electrode has good electrical conductivity. The Rct is 0.126 Ω, low Rct means high electrical conductivity and good wettability [44]. When the frequency is low, the line is close to 90°, which denotes the idealized capacitance behaviour of the biochar material. As can be seen from Fig. 6e, after 36,000 cycles at 5 A g−1, the biochar electrode exhibits a high reversible capacitance 279.9 F g−1, suggesting superior cycling stability of the biochar electrode. The increased specific capacitance after 36,000 cycles may be thanks to the multi-stage pore structure, and electrolyte ions are more easily reached on the surface of the active material. Furthermore, multiple charge and discharge causes the electrode material to be fully infiltrated and more active sites are excited [45–47].
Yanhong Li: Investigation, Data curation, Writing - original draft. Xin Zhang: Writing - review & editing. Jiaying Deng: Investigation. Xiaheng Yang: Resources. Jinlong Wang: Data curation. Yanzhi Wang: Conceptualization, Project administration. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. References [1] Y.H. Cao, K.L. Wang, X.M. Wang, Z.R. Gu, Q.H. Fan, W. Gibbons, J.D. Hoefelmeyer, P.R. Kharel, M. Shrestha, Electrochim. Acta 212 (2016) 839–847, https://doi.org/ 10.1016/j.electacta.2016.07.069. [2] B. Kirubasankar, V. Murugadoss, J. Lin, T. Ding, M. Dong, H. Liu, J. Zhang, T.X. Li, N. Wang, Z.H. Guo, S. Angaiah, Nanoscale. 10 (2018) 20414–20425, https://doi. org/10.1039/c8nr06345a. [3] S.E.M. Pourhosseinia, O. Norouzia, H.R. Naderi, Biomass Bioenergy 107 (2017) 287–298, https://doi.org/10.1016/j.biombioe.2017.10.025. [4] N.F. He, S. Yoo, J.J. Meng, O. Yildiz, P.D. Bradford, S. Park, W. Gao, Carbon. 120 (2017) 304–312, https://doi.org/10.1016/j.carbon.2017.05.056. [5] X.F. Tan, S.B. Liu, Y.G. Liu, Y.L. Gu, G.M. Zeng, X.J. Hu, X. Wang, S.H. Liu, L.H. Jiang, Bioresour. Technol. 227 (2017) 359–372, https://doi.org/10.1016/j. biortech.2016.12.083. [6] J. Pallarés, A. González-Cencerrado, I. Arauzo, Biomass Bioenergy 115 (2018) 64–73, https://doi.org/10.1016/j.biombioe.2018.04.015. [7] K. Wang, N. Zhao, S.W. Lei, R. Yan, X.D. Tian, J.Z. Wang, Y. Song, D.F. Xu, Q.G. Guo, L. Liu, Electrochim. Acta 166 (2015) 1–11, https://doi.org/10.1016/j. electacta.2015.03.048. [8] A.M. Dehkhoda, E. Gyenge, N. Ellis, Biomass Bioenergy 87 (2016) 107–121, https://doi.org/10.1016/j.biombioe.2016.02.023. [9] Md. AzharulIslam, M.J. Ahmed, W.A. Khanday, M. Asif, B.H. Hameed, Ecotoxicol. Environ. Saf. 138 (2017) 279–285, https://doi.org/10.1016/j.ecoenv.2017.01.010. [10] X. Du, W. Zhao, Y. Wang, C.Y. Wang, M.M. Chen, T. Qi, C. Hua, M.G. Ma, Bioresour. Technol. 149 (2013) 31–37, https://doi.org/10.1016/j.biortech.2013.09.026. [11] Y.H. Cao, X.M. Wang, Z.G. Gua, Q.H. Fan, W. Gibbons, V. Gadhamshettyd, N. Aie, G.N. Zeng, J. Power Sources 384 (2018) 360–366, https://doi.org/10.1016/j. jpowsour.2018.02.079. [12] M. Myglovets, O.I. Poddubnaya, O. Sevastyanova, M.E. Lindstrom, B. Gawdzik, M. Sobiesiak, M.M. Tsyba, V.I. Sapsay, D.O. Klymchuk, A.M. Puziy, Carbon 80 (2014) 771–783, https://doi.org/10.1016/j.carbon.2014.09.032. [13] Dr. Y. Shen, T.T Qu, K. Xiang, Y. Zhang, Prof. Z.F Tian, Prof. M.J. Xie, Prof. X.F. Gu, Chem. Select. 2 (2017) 10704−10708. https://doi.org/10.1002/slct.201702050. [14] L.J. Xie, G.H. Sun, F.Y. Su, X.Q. Guo, Q.Q. Kong, X.M. Li, X.H. Huang, L. Wan, W. song, K.X. Li, C.X. Lv, C.M. Chen, J. Mater. Chem. A. 4 (2016) 1637−1646. https:// doi.org/10.1039/C5TA09043A. [15] K.R. Thines, E.C. Abdullah, N.M. Mubarak, M. Ruthiraan, Renew. Sustain. Energy Rev. 67 (2017) 257–276, https://doi.org/10.1016/j.rser.2016.09.057. [16] G.J. Yang, S.J. Park, J. Alloy. Compd. 741 (2018) 360–367, https://doi.org/10. 1016/j.jallcom.2018.01.108. [17] J. Ding, H.L. Wang, Z. Li, K. Cui, D. Karpuzov, X.H. Tan, A. Kohandehghanab, D. Mitlin, Energy Environ. Sci. 8 (2015) 941–955, https://doi.org/10.1039/ c4ee02986k. [18] J.M. Jung, J.I. Oh, K. Baek, J. Lee, E.E. Kwon, Energy Convers. Manage. 165 (2018) 628–633, https://doi.org/10.1016/j.enconman.2018.03.096. [19] D. Pontirolia, S. Scaravonati, G. Magnani, L. Fornasini, D. Bersani, G. Bertoni,
4. Conclusions The hierarchical porous biochar was prepared from cotinus 6
Chemical Physics Letters 747 (2020) 137325
Y. Li, et al.
[20] [21] [22]
[23] [24] [25] [26] [27] [28] [29]
[30] [31] [32]
[33]
10.15376/biores.12.2.3340-3350. [34] J. Hayashi, T. Horikawa, I. Takeda, K. Muroyama, F.N. Ani, Carbon 40 (2002) 2381–2386. [35] X.H. Zhang, K. Zhang, H.X. Li, Q. Wang, L. Jin, Q. Cao, J. Appl. Electrochem. 48 (2018) 415–426, https://doi.org/10.1007/s10800-018-1170-x. [36] X.L. Su, M.Y. Cheng, L. Fu, J.H. Yang, X.C. Zheng, X.X. Guan, J. Power Sources 362 (2017) 27–38, https://doi.org/10.1016/j.jpowsour.2017.07.021. [37] J.M. Nabais, J.G. Teixeira, I. Almeida, Bioresour. Technol. 102 (2011) 2781–2787, https://doi.org/10.1016/j.biortech.2010.11.083. [38] D. Kalpana, S. Cho, S. Lee, Y. Lee, R. Misra, N. Renganathan, J. Power Sources 190 (2009) 587–591, https://doi.org/10.1016/j.jpowsour.2009.01.058. [39] P. González-García, T.A. Centeno, E. Urones-Garrote, D. Ávila-Brande, L.C. OteroDíaz, Appl. Surf. Sci. 265 (2013) 731–737, https://doi.org/10.1016/j.apsusc.2012. 11.092. [40] C. Liang, J.P. Bao, C.G. Li, H. Huang, C.L. Chen, Y. Lou, H.Y. Lu, H.B. Lin, Z. Shi, S.H. Feng, Micropor. Mesopor. Mater. 251 (2017) 77–82, https://doi.org/10.1016/ j.micromeso.2017.05.044. [41] J.W. Qi, W.D. Zhang, L. Xu, Chem. Eur. J. 24 (2018) 18097–18105, https://doi.org/ 10.1002/chem.201804302. [42] K.S. Xia, Q.M. Gao, J.H. Jiang, J. Hu, Carbon 46 (2008) 1718–1726, https://doi. org/10.1016/j.carbon.2008.07.018. [43] P. Abudu, L.X. Wang, M.J. Xu, D.Z. Jia, X.C. Wang, L.X. Jia, Chem. Phys. Lett. 702 (2018) 1–7, https://doi.org/10.1016/j.cplett.2018.04.055. [44] M. Genovese, H. Wu, A. Virya, J. Li, P.Z. Shen, K. Lian, Electrochim. Acta 273 (2018) 392–401, https://doi.org/10.1016/j.electacta.2018.04.061. [45] O.Y. Yu, R.J. Huang, X.F. Xia, H.T. Ye, X.Y. Jiao, L. Wang, W. Lei, Q.L. Hao, Chem. Eng. J. 355 (2019) 416–427, https://doi.org/10.1016/j.cej.2018.08.142. [46] D.Y. Lei, K.H. Song, X.D. Li, H.Y. Kim, B.S. Kim, J. Mater. Sci. 52 (2017) 2158–2168, https://doi.org/10.1007/s10853-016-0504-5. [47] P.Z. Wang, W.X. Luo, N.N. Guo, L.X. Wang, D.Z. Jia, Z.B. Zhao, S. Zhang, M.J. Xu, Chem. Phys. Lett. 730 (2019) 32–38, https://doi.org/10.1016/j.cplett.2019.05. 032.
C. Milanese, A. Girella, F. Ridi, R. Verucchi, L. Mantovani, A. Malcevschi, M. Riccò, Microporous Mesoporous Mater. 285 (2019) 161–169, https://doi.org/10.1016/j. micromeso.2019.05.002. Y.H. Fu, N.Y. Zhang, Y.F. Shen, X.L. Ge, M.D. Chen, Bioresour. Technol. 269 (2018) 67–73, https://doi.org/10.1016/j.biortech.2018.08.083. M. Marc̆etić, D. Boz̆ić, M. Milenković, N. Males̆ević, Sinis̆a Radulović, N. Kovac̆ević, Phytother. Res. 27 (2013) 1658–1663. https://doi.org/10.1002/ptr.4919. ̆ K. Savikina, G. Zdunić, T. Janković, T. Stanojković, Z. Juranić, Nebojs̆a Menković, Nat. Prod. Res. 18 (2009) 1731−1739. https://doi.org/10.1080/ 14786410802267650. X.L. Su, S. Jiang, G.P. Zheng, X.C. Zheng, J.H. Yang, Z.Y. Liu, J. Mater. Sci. 53 (2018) 9191–9205, https://doi.org/10.1007/s10853-018-2208-5. A.M. Dehkhoda, N. Ellis, E. Gyenge, Micropor. Mesopor. Mater. 224 (2016) 217–228, https://doi.org/10.1016/j.micromeso.2015.11.041. K. Wang, Y. Song, R. Yan, N. Zhao, X.D. Tian, X. Li, Q.G. Guo, Z.J. Liu, Appl. Surf. Sci. 394 (2017) 569–577, https://doi.org/10.1016/j.apsusc.2016.10.161. X.L. Su, S.H. Li, S. Jiang, Z.K. Peng, X.X. Guan, X.C. Zheng, Adv. Powder Technol. 29 (2018) 2097–2107, https://doi.org/10.1016/j.apt.2018.05.018. M. Genovese, K. Lian, J. Mater. Chem. A 5 (2017) 3939–3947, https://doi.org/10. 1039/c6ta10382k. Y.Y. Liu, G.X. Dai, L.J. Zhu, S.R. Wang, ChemElectroChem. 13 (2018) 287–288, https://doi.org/10.1002/celc.201801272. Z.P. Qiu, Y.S. Wang, X. Bi, T. Zhou, J. Zhou, J.P. Zhao, Z.C. Miao, W.M. Yi, P. Fu, S.P. Zhuo, J. Power Sources 376 (2018) 82–90, https://doi.org/10.1016/j. jpowsour.2017.11.077. S. Yang, S.L. Wang, X. Liu, L. Li, Carbon 147 (2019) 540–549, https://doi.org/10. 1016/j.carbon.2019.03.023. A.G. Pandolfo, A.F. Hollenkamp, J. Power Sources. 157 (2006) 11–27. https:// doi. org/10.1016/j.jpowsour.2006.02.065. S. Zhang, C.L. Wu, W. Wu, C. Zhou, Z.W. Xi, Y.Y. Deng, X. Wang, P. Quan, X.J. Li, Y.F. Luo, J. Power Sources 424 (2019) 1–7, https://doi.org/10.1016/j.jpowsour. 2019.03.100. X.F. Li, W.T. Chen, L.Q. Dou, BioResources 12 (2017) 3340–3350, https://doi.org/
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