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A volume-porous conductive electrode by hexagonal close packing of phenolic resin-based carbon spheres
Accepted Manuscript A volume-porous conductive electrode by hexagonal close packing of phenolic resin-based carbon spheres Yongbeom Kim, Joonhyeon Jeon PII: DOI: Reference:
S0167-577X(19)31065-1 https://doi.org/10.1016/j.matlet.2019.07.079 MLBLUE 26450
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
5 April 2019 18 July 2019 19 July 2019
Please cite this article as: Y. Kim, J. Jeon, A volume-porous conductive electrode by hexagonal close packing of phenolic resin-based carbon spheres, Materials Letters (2019), doi: https://doi.org/10.1016/j.matlet.2019.07.079
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A volume-porous conductive electrode by hexagonal close packing of phenolic resin-based carbon spheres Yongbeom Kim, Joonhyeon Jeon* Division of electronic & electrical engineering, Dongguk university, Seoul, republic of Korea [email protected], *[email protected] Abstract: This paper describes a volume-porous electrode by carbonizing a hexagonally close packing of phenolic resin spheres. The proposed volume-porous electrode comprises an amorphous carbon of high purity above 99.9% and its triangle-shape pores, which are controllable according to phenolic-resin-sphere size, are uniformly distributed in three dimensions. In addition, this volume-porous electrode has a porosity of about 37% and high conductivity above 5.05 Scm-1, and it allows fluid (liquid or gas) to flow through a volume of the electrode in three orthogonal directions. 1. Introduction Secondary batteries have attracted substantial attention due to the rapidly increasing demand for electric vehicles and large-capacity energy storage devices. The electrodes that can be used for secondary batteries can be distinguished into surface electrodes and volume electrodes according to the battery types, and the electrode materials have a decisive effect on the battery performance. Recently, the development of fuel cells [1] and flow batteries [2] has required the use of carbon-based volume electrodes with a porous and conductive structure. Many studies have been carried out to improve the conductivities of such volume-porous electrodes [1, 2, 3, 4, 5, 6, 7,8]. For example, in 2007 and 2013, W.H. Wang [4] and Y. Munaiah [5] respectively reported on the use of iridium and carbon nanotube (CNT) coatings on carbon fiber for flow battery. Recently, both X. Xie [6] and N. Zhao [7] have also suggested the use of CNT coating on carbon-fiber in order to improve the electrode conductivity of microbial fuel cell (MFC). However, their methods involve adding another coating process, not developing a new material-based carbon electrode, and are not costeffective for commercial use in products. Despite these efforts, there still remains a problem in materializing a cost-effective, and highly conductive electrode with a volume porous structure. This paper describes a cost-effective, and highly conductive electrode with a volume-porous structure, which comprises a phenolic resin-based amorphous carbon spheres. In order tTo demonstrate the effectiveness of the proposed carbon-based volume electrode, the results of the experiments are analyzed using Energy Dispersive X-Ray Spectroscopy (EDS), Inductively Coupled Plasma Mass Spectrometry(ICP-MS), Brunauer–Emmett–Teller (BET), X-raty diffraction pattern (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Raman spectroscopy, cyclic voltammetry (CV), and conductivity measurement. This paper provides new insight into the use of a new volumeporous electrode, and the carbonized phenolic-resin-sphere electrode has to be considered for various applications, such as fuel cells and flow batteries. 2. Preparation of Carbonized Volume-Porous Electrode 1
The proposed carbonized volume-porous electrode (CVPE) is was prepared through the process shown in Fig. 1. In addition, eEach process is summarized in further detail below in the following.
Fig. 1. (a) Procedure for CVPE, (b) hardened phenolic resin spheres, and (c) CVPE surface (size and thickness of 100x100x3mm) with uniformly distributed pores (x130 magnification) Production of phenolic resin spheres: In order to prepare a phenolic resin mixture, polyvinyl alcohol ([CH2CHOH]n 0.9wt%), ethanol (C2H5OH 19.8wt%), hexamethylenetetramine ((CH2)6N4 8.2wt%), KOH(0.9wt%), and DI water(61.9wt%) are were stirred with phenolic resin (8.3wt%). Then, polyvinyl alcohol, hexamethylenetetramine, and KOH are were used for dispersion, hardening, and pH control (pH 6 to 7), respectively. The stirring operation continuesd for 24 hours and the phenolic resin mixture was stabilized at room temperature for 24 hours again. In order tTo obtain phenolic resin spheres from the mixture, a sphericalization and hardening processes is were carried out for 70 to 90 minutes using a baffled stirrer with 150 to 300 rpm at 80 ℃ or more. Then, the size of the hardened phenolic
2
resin spheres is determined according to the stirring rpm, and the experimental result is presented in Table S1. Sphere packing: In order tTo ensure the close-packing of the phenolic resin spheres (i.e., making a volume porous electrode), the prepared phenolic resin spheres are were mixed with 5-10 wt% of resole-type phenolic resin used as a binder, and the mixture is was packed and flattened at 30kg/Pa in the packing frame of the press machine so as to form a volume-porous electrode. The thickness and size of the electrode are were determined by the stainless-steel mold used for the phenolic resin sphere packing. Then, the vibration of 10 Hz is was given to form the hexagonal structures of spheres, and the heating at a temperature of 100 ℃ is was supplied so that the phenolic resole resin could forms an interface bond between the phenolic resin spheres. In this hardening process of heat treatment together with vibration, the hexagonal formation of spheres can could lead to a large active-surface area, uniform distribution of pores, and strong multiple bonds between spheres as compared to other structures such as square lattice. Carbonization: The phenolic resin sphere packing of board type is was carbonized in the a furnace (Komax Carbon Co.) under a vacuum condition at a temperature of 1800 ℃. The carbonization is carried out during over 24 hours, and then, oxygen and hydrogen components contained in the phenolic resin of sphere packing are were gasified and released outside. After the carbonization, the content of carbon almost reachesd more than 98% and but there still remains potassium of less than 2%. This carbonization at high temperature allowsed the formation of a carbonized volume porous electrode (CVPE) with a high conductivity. High purification: High purification, which is a process used to remove the potassium attached on the surface of the CVPE, is was carried out by heating the CVPE in a furnace (IHI - VFCP - 2200) under nitrogen atmosphere at a temperature of 2100 ℃. The purity of the CVPE is was maximized by repeating the insertion and removal of hydrogen chloride gas for two hours 12 times. Fig.S1 shows the EDS spectrum to measure the carbon purity of a CVPE sample and IPC-MS data is also indicated in Table S2. Consequently, this leads to the content of carbon potentially exceeding 99.9% in the CVPE. In addition, entire characterization in a preparation process of the CVPE is summarized in Table S3. 3. Results and Discussion In order tTo show the effectiveness of the proposed CVPE, various fundamental properties including electrochemical characteristics are were measured and analyzed through various measurement devices. Four CVPEs with a thickness and size of 3mm x 4cm2 are were used in this work, and they are were produced with one of the four phenolic-resin sphere diameters of 100µm, 250µm, 350µm, and 450µm (Table S1). The morphologies of the proposed CVPEs are shown in Fig. 2, and Table S4 also presents the carbonization-shrinkage ratio, pore size, surface area and the CVPE porosity according to the diameter of the phenolic resin spheres. In addition, pore distribution is indicated in Fig S2. In Fig. 2, it can be seen that the triangle-shaped pores are were formed very well regardless of the sphere sizes, and also that the pore size also increases with the carbon-sphere diameter. In addition, it appears that 3
the diameters of carbonized spheres arewere equally reduced to about 24%, regardless of their original size, and the porosities of the CVPEs are were also equal to about 37% (Table S4). In other words, while their reaction surface iswas the same regardless of the carbonized sphere size, the flow velocity can increase with increasing pore size (i.e., carbon-sphere size). Especially, it appears that the CVPE the pores arewere numerously and evenly distributed in the range of 85~ 125 μm.
Fig. 2. x600 magnification morphology of CVPE pores due to phenolic resin sphere diameters of (a) 100㎛, (b) 250㎛, (c) 350㎛, and (d) 450㎛ Fig.3 shows the carbonization properties, including the hybridization and molecular structure of the CVPE. As shown in Fig. 3(a), the Raman spectroscopy of the CVPE shows a D-band and a G-band centered at 1352 cm-1 and 1592 cm-1, respectively., Aand the i(D)/i(G) ratio is 1.69. The appearance of the two bands reflects the presence of sp2 and sp3 bonds, respectively, and also indicates the presence of amorphous carbon [9]. This can also be supported by XPS and XRD. The high-resolution XPS of the CVPE is presented in Fig. 3(b), wherein the Su1s spectrum exhibits only a main C1s peak at 282.4 eV, implying that carbon is mostly present in the sp2 hybridization state and the carbonization of CVPE is completed [9]. Meanwhile, the inset in Fig. 3(b) shows that the C1s narrow scan of the CVPE is deconvoluted into three peaks: an sp2 peak at 284.5eV, sp3 peak at 285.4eV, and C-O peak at 286.3eV. In addition, it can be seen from Fig S3 that the XRD pattern also has broad peaks of (002) and (101). Consequently, it can be said that the proposed CVPE has an amorphous 4
structure [10,11,12]. In order to simulate the electrochemical properties of CVPE for a flow battery application, CV measurement iswas carried out. Then, a CVPE (using phenolic resin spheres of diameter 450μm) with a size of 1cm2 is used as a working electrode, where the potential scanning range is from -1.2 V to 0.2 V and from 0.0 V to 0.9 V with a scan rate of 30 mV s-1. In addition, 0.5M vanadium electrolyte and 0.5 M zinc-bromine electrolyte are employed for the CV experiments as well, which are well-known as flow battery electrolytes. Fig. 3(c) and Fig. 3(d) show the CV curves, and the measurement data are presented in Table S5. These results demonstrate that the proposed CVPE provides excellent reversibility and stability in both of the electrolytes. In addition, the electrical conductivity of CVPE is shown in Table S6, where the size and thickness of the sample are shown to be 4 cm2 and 3mm, respectively. It appears that the electrical conductivity of the CVPE increases as the sphere size in the CVPE increases, resulting in the highest conductivity of 5.056833 S/cm (0.020463 Ω) when the CVPE iswas carbonized with phenolic resin spheres with a diameter of 450μm. This is due to the fact that because using large-size spheres provides lower contact resistance than using small-size spheres.
Fig. 3. Carbonization properties of CVPE: (a) Raman spectrum (Ar-ion laser of 514.5nm as excitation source), (b) XPS (Al Kα X-rays (1486.6 eV), 100W) Su1s and C1s narrow spectrum, and CV measurements of (c) 0.5M VOSO4 1.2M H2SO4 electrolyte and (d) 0.5M ZnBr2 electrolyte. 5
4. Conclusions This paper has proposed a CVPE by carbonizing phenolic-resin-spheres, which is applicable as a volume-porous electrode toin fuel cells and flow batteries. The experimental results have shown that the proposed CVPE has an amorphous carbon structure with a purity above 99.9%, and its triangle-shape pores, which are controllable according to the phenolicresin-sphere size, are uniformly distributed to flow liquid and gas materials. In addition, this CVPE has been shown to provide high electrical and electrochemical performance for the application of flow batteries. This paper provides significant insight into a new volumeporous electrode. Acknowledgement This work was funded by the Dongguk University Research Fund of 2018 (S-2018-G000100037) and by the Korea Institute of Energy Technology Evaluation and Planning(KETEP) a nd the Ministry of Trade, Industry & Energy(MOTIE) of the Republic of Korea (no. 2019403 0202320). 6. Reference [1] Michio Inagaki, Jieshan Qiu, Quangui Guo, Carbon foam : preparation and application, Carbon 87 (2015) 128-152 [2] Donghyeon Kim, Yongbeom Kim, Youngho Lee, Joonhyeon Jeon, 1,2Dimethylimidazole based bromine complexing agents for vanadium bromine redox flow batteries, International Journal of Hydrogen Energy, 44 (2019) 12024-12032 [3] Junxian Hou, Zhongliang Liu, Yanxia Li, Siqi Yang, Yu Zhou, A comparative study of graphene-coated stainless steel fiber felt and carbon cloth as anodes in MFCs, Bioprocess Biosyst Eng 38(5) (2015) 881-888 [4] Y. Munaiah, S.dheenadayalan, P. Ragupathy, Vijayamohanan K. Pillai, High Performance Carbon Nanotube Based Electrodes for Zinc Bromine Redox Flow Batteries, ECS Jounal of Solide State Science and Technology, 2(1) (2013) M3182-3186 [5] W.H.Wang, X.D.Wang, Investigation of Ir-modified carbon felt as the positive electrode of an all-vanadium redox flow battery, Electrochimica Acta 52 (2007) 6755-6762 [6] Xing Xie, Meng Ye, Liangbing Hu, Nian Liu, James R. McDonough, Wei Chen, H. N. Alshareef, Craig S. Criddle, Yi Cui, Carbon nanotube-coated macroporous sponge for microbial fule cell electrode, The Royal Society of Chemistry Energy Environ. Sci. 5 (2012) 5265-5270 [7] Na Zhao, Zhaokun Ma, Huaihe Song, Yangen Xie, Man Zhang, Enhancement of bioelectricity generation by synergistic modification of vertical carbon nanotubes/polypyrrole for the carbon fibers anode in microbial fuel cell, Electrochimica Acta 296 (2019) 69-74 [8] Zhisheng Lv, Daohai Xie, Xianjun Yue, Chunhua Feng, Chaohai Wei, Ruthenium oxidecoated carbon felt electrode : A highly active anode for microbial fuel cell applications, Journal of Power Sources, 210 (2012) 26-31 [9] John Mcdonalad-Wharry, Merilyn Manly-Harris, Kim pickering, Carbonisation of biomass-derived chars and the thermal reduction of a graphene oxide sample studied using Raman spectroscopy, Carbon 59 (2013) 383-405 [10] DongRak Sohn, Jong Wan KO, Eun Jin Son, Sung Hyun Ko, Tae-Hee Kim, HyukSang Kwon, Chan Beum Park, Cellulos-Templated, Dual-Carbonized Na3V2(PO4)3 for Energy Storage with High Rate Capability, ChemElectroChem 5 (2018) 2186-2191 6
[11] Fang Zhao, Andrei Vrajitoarea, Qi Jiang, Xiaoyu Han, Aysha Chaudhary, Joseph O. Welch , Richard B. Jackman, Graphene-Nanodiamond Heterostructures and their application to High Current Device, Nature Scientific Reports 5 (2015) 13771 [12] Yunming Li, Shuyin Xu, Xiaoyan Wu, Juezhi Yu, Yuesheng Wang, Yong-Sheng Hu, Hong Li, Liquan Chen and Xuejie Huang, Amorphous monodispersed hard carbon microspherules derived from biomass as a high performance negative electrode material for sodium-ion batteries, Royal Society of Chemistry J. Mater. Chem. A, 3 (2015) 71-77
7
Highlights ○ A volume-porous electrode is to carbonize a close packing of phenolic resin spheres. ○ Liquid or gas fluid flow is allowed through the pore spaces of the electrode. ○ Well-controlled and uniformly-distributed pores of triangle-shape are comprised. ○ A amorphous carbon of high purity above 99.9% is formed. ○ High porosity of about 37% and high conductivity above 5.05 Scm-1 are resulted. .
8
S0167-577X(19)31065-1 https://doi.org/10.1016/j.matlet.2019.07.079 MLBLUE 26450
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
5 April 2019 18 July 2019 19 July 2019
Please cite this article as: Y. Kim, J. Jeon, A volume-porous conductive electrode by hexagonal close packing of phenolic resin-based carbon spheres, Materials Letters (2019), doi: https://doi.org/10.1016/j.matlet.2019.07.079
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A volume-porous conductive electrode by hexagonal close packing of phenolic resin-based carbon spheres Yongbeom Kim, Joonhyeon Jeon* Division of electronic & electrical engineering, Dongguk university, Seoul, republic of Korea [email protected], *[email protected] Abstract: This paper describes a volume-porous electrode by carbonizing a hexagonally close packing of phenolic resin spheres. The proposed volume-porous electrode comprises an amorphous carbon of high purity above 99.9% and its triangle-shape pores, which are controllable according to phenolic-resin-sphere size, are uniformly distributed in three dimensions. In addition, this volume-porous electrode has a porosity of about 37% and high conductivity above 5.05 Scm-1, and it allows fluid (liquid or gas) to flow through a volume of the electrode in three orthogonal directions. 1. Introduction Secondary batteries have attracted substantial attention due to the rapidly increasing demand for electric vehicles and large-capacity energy storage devices. The electrodes that can be used for secondary batteries can be distinguished into surface electrodes and volume electrodes according to the battery types, and the electrode materials have a decisive effect on the battery performance. Recently, the development of fuel cells [1] and flow batteries [2] has required the use of carbon-based volume electrodes with a porous and conductive structure. Many studies have been carried out to improve the conductivities of such volume-porous electrodes [1, 2, 3, 4, 5, 6, 7,8]. For example, in 2007 and 2013, W.H. Wang [4] and Y. Munaiah [5] respectively reported on the use of iridium and carbon nanotube (CNT) coatings on carbon fiber for flow battery. Recently, both X. Xie [6] and N. Zhao [7] have also suggested the use of CNT coating on carbon-fiber in order to improve the electrode conductivity of microbial fuel cell (MFC). However, their methods involve adding another coating process, not developing a new material-based carbon electrode, and are not costeffective for commercial use in products. Despite these efforts, there still remains a problem in materializing a cost-effective, and highly conductive electrode with a volume porous structure. This paper describes a cost-effective, and highly conductive electrode with a volume-porous structure, which comprises a phenolic resin-based amorphous carbon spheres. In order tTo demonstrate the effectiveness of the proposed carbon-based volume electrode, the results of the experiments are analyzed using Energy Dispersive X-Ray Spectroscopy (EDS), Inductively Coupled Plasma Mass Spectrometry(ICP-MS), Brunauer–Emmett–Teller (BET), X-raty diffraction pattern (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Raman spectroscopy, cyclic voltammetry (CV), and conductivity measurement. This paper provides new insight into the use of a new volumeporous electrode, and the carbonized phenolic-resin-sphere electrode has to be considered for various applications, such as fuel cells and flow batteries. 2. Preparation of Carbonized Volume-Porous Electrode 1
The proposed carbonized volume-porous electrode (CVPE) is was prepared through the process shown in Fig. 1. In addition, eEach process is summarized in further detail below in the following.
Fig. 1. (a) Procedure for CVPE, (b) hardened phenolic resin spheres, and (c) CVPE surface (size and thickness of 100x100x3mm) with uniformly distributed pores (x130 magnification) Production of phenolic resin spheres: In order to prepare a phenolic resin mixture, polyvinyl alcohol ([CH2CHOH]n 0.9wt%), ethanol (C2H5OH 19.8wt%), hexamethylenetetramine ((CH2)6N4 8.2wt%), KOH(0.9wt%), and DI water(61.9wt%) are were stirred with phenolic resin (8.3wt%). Then, polyvinyl alcohol, hexamethylenetetramine, and KOH are were used for dispersion, hardening, and pH control (pH 6 to 7), respectively. The stirring operation continuesd for 24 hours and the phenolic resin mixture was stabilized at room temperature for 24 hours again. In order tTo obtain phenolic resin spheres from the mixture, a sphericalization and hardening processes is were carried out for 70 to 90 minutes using a baffled stirrer with 150 to 300 rpm at 80 ℃ or more. Then, the size of the hardened phenolic
2
resin spheres is determined according to the stirring rpm, and the experimental result is presented in Table S1. Sphere packing: In order tTo ensure the close-packing of the phenolic resin spheres (i.e., making a volume porous electrode), the prepared phenolic resin spheres are were mixed with 5-10 wt% of resole-type phenolic resin used as a binder, and the mixture is was packed and flattened at 30kg/Pa in the packing frame of the press machine so as to form a volume-porous electrode. The thickness and size of the electrode are were determined by the stainless-steel mold used for the phenolic resin sphere packing. Then, the vibration of 10 Hz is was given to form the hexagonal structures of spheres, and the heating at a temperature of 100 ℃ is was supplied so that the phenolic resole resin could forms an interface bond between the phenolic resin spheres. In this hardening process of heat treatment together with vibration, the hexagonal formation of spheres can could lead to a large active-surface area, uniform distribution of pores, and strong multiple bonds between spheres as compared to other structures such as square lattice. Carbonization: The phenolic resin sphere packing of board type is was carbonized in the a furnace (Komax Carbon Co.) under a vacuum condition at a temperature of 1800 ℃. The carbonization is carried out during over 24 hours, and then, oxygen and hydrogen components contained in the phenolic resin of sphere packing are were gasified and released outside. After the carbonization, the content of carbon almost reachesd more than 98% and but there still remains potassium of less than 2%. This carbonization at high temperature allowsed the formation of a carbonized volume porous electrode (CVPE) with a high conductivity. High purification: High purification, which is a process used to remove the potassium attached on the surface of the CVPE, is was carried out by heating the CVPE in a furnace (IHI - VFCP - 2200) under nitrogen atmosphere at a temperature of 2100 ℃. The purity of the CVPE is was maximized by repeating the insertion and removal of hydrogen chloride gas for two hours 12 times. Fig.S1 shows the EDS spectrum to measure the carbon purity of a CVPE sample and IPC-MS data is also indicated in Table S2. Consequently, this leads to the content of carbon potentially exceeding 99.9% in the CVPE. In addition, entire characterization in a preparation process of the CVPE is summarized in Table S3. 3. Results and Discussion In order tTo show the effectiveness of the proposed CVPE, various fundamental properties including electrochemical characteristics are were measured and analyzed through various measurement devices. Four CVPEs with a thickness and size of 3mm x 4cm2 are were used in this work, and they are were produced with one of the four phenolic-resin sphere diameters of 100µm, 250µm, 350µm, and 450µm (Table S1). The morphologies of the proposed CVPEs are shown in Fig. 2, and Table S4 also presents the carbonization-shrinkage ratio, pore size, surface area and the CVPE porosity according to the diameter of the phenolic resin spheres. In addition, pore distribution is indicated in Fig S2. In Fig. 2, it can be seen that the triangle-shaped pores are were formed very well regardless of the sphere sizes, and also that the pore size also increases with the carbon-sphere diameter. In addition, it appears that 3
the diameters of carbonized spheres arewere equally reduced to about 24%, regardless of their original size, and the porosities of the CVPEs are were also equal to about 37% (Table S4). In other words, while their reaction surface iswas the same regardless of the carbonized sphere size, the flow velocity can increase with increasing pore size (i.e., carbon-sphere size). Especially, it appears that the CVPE the pores arewere numerously and evenly distributed in the range of 85~ 125 μm.
Fig. 2. x600 magnification morphology of CVPE pores due to phenolic resin sphere diameters of (a) 100㎛, (b) 250㎛, (c) 350㎛, and (d) 450㎛ Fig.3 shows the carbonization properties, including the hybridization and molecular structure of the CVPE. As shown in Fig. 3(a), the Raman spectroscopy of the CVPE shows a D-band and a G-band centered at 1352 cm-1 and 1592 cm-1, respectively., Aand the i(D)/i(G) ratio is 1.69. The appearance of the two bands reflects the presence of sp2 and sp3 bonds, respectively, and also indicates the presence of amorphous carbon [9]. This can also be supported by XPS and XRD. The high-resolution XPS of the CVPE is presented in Fig. 3(b), wherein the Su1s spectrum exhibits only a main C1s peak at 282.4 eV, implying that carbon is mostly present in the sp2 hybridization state and the carbonization of CVPE is completed [9]. Meanwhile, the inset in Fig. 3(b) shows that the C1s narrow scan of the CVPE is deconvoluted into three peaks: an sp2 peak at 284.5eV, sp3 peak at 285.4eV, and C-O peak at 286.3eV. In addition, it can be seen from Fig S3 that the XRD pattern also has broad peaks of (002) and (101). Consequently, it can be said that the proposed CVPE has an amorphous 4
structure [10,11,12]. In order to simulate the electrochemical properties of CVPE for a flow battery application, CV measurement iswas carried out. Then, a CVPE (using phenolic resin spheres of diameter 450μm) with a size of 1cm2 is used as a working electrode, where the potential scanning range is from -1.2 V to 0.2 V and from 0.0 V to 0.9 V with a scan rate of 30 mV s-1. In addition, 0.5M vanadium electrolyte and 0.5 M zinc-bromine electrolyte are employed for the CV experiments as well, which are well-known as flow battery electrolytes. Fig. 3(c) and Fig. 3(d) show the CV curves, and the measurement data are presented in Table S5. These results demonstrate that the proposed CVPE provides excellent reversibility and stability in both of the electrolytes. In addition, the electrical conductivity of CVPE is shown in Table S6, where the size and thickness of the sample are shown to be 4 cm2 and 3mm, respectively. It appears that the electrical conductivity of the CVPE increases as the sphere size in the CVPE increases, resulting in the highest conductivity of 5.056833 S/cm (0.020463 Ω) when the CVPE iswas carbonized with phenolic resin spheres with a diameter of 450μm. This is due to the fact that because using large-size spheres provides lower contact resistance than using small-size spheres.
Fig. 3. Carbonization properties of CVPE: (a) Raman spectrum (Ar-ion laser of 514.5nm as excitation source), (b) XPS (Al Kα X-rays (1486.6 eV), 100W) Su1s and C1s narrow spectrum, and CV measurements of (c) 0.5M VOSO4 1.2M H2SO4 electrolyte and (d) 0.5M ZnBr2 electrolyte. 5
4. Conclusions This paper has proposed a CVPE by carbonizing phenolic-resin-spheres, which is applicable as a volume-porous electrode toin fuel cells and flow batteries. The experimental results have shown that the proposed CVPE has an amorphous carbon structure with a purity above 99.9%, and its triangle-shape pores, which are controllable according to the phenolicresin-sphere size, are uniformly distributed to flow liquid and gas materials. In addition, this CVPE has been shown to provide high electrical and electrochemical performance for the application of flow batteries. This paper provides significant insight into a new volumeporous electrode. Acknowledgement This work was funded by the Dongguk University Research Fund of 2018 (S-2018-G000100037) and by the Korea Institute of Energy Technology Evaluation and Planning(KETEP) a nd the Ministry of Trade, Industry & Energy(MOTIE) of the Republic of Korea (no. 2019403 0202320). 6. Reference [1] Michio Inagaki, Jieshan Qiu, Quangui Guo, Carbon foam : preparation and application, Carbon 87 (2015) 128-152 [2] Donghyeon Kim, Yongbeom Kim, Youngho Lee, Joonhyeon Jeon, 1,2Dimethylimidazole based bromine complexing agents for vanadium bromine redox flow batteries, International Journal of Hydrogen Energy, 44 (2019) 12024-12032 [3] Junxian Hou, Zhongliang Liu, Yanxia Li, Siqi Yang, Yu Zhou, A comparative study of graphene-coated stainless steel fiber felt and carbon cloth as anodes in MFCs, Bioprocess Biosyst Eng 38(5) (2015) 881-888 [4] Y. Munaiah, S.dheenadayalan, P. Ragupathy, Vijayamohanan K. Pillai, High Performance Carbon Nanotube Based Electrodes for Zinc Bromine Redox Flow Batteries, ECS Jounal of Solide State Science and Technology, 2(1) (2013) M3182-3186 [5] W.H.Wang, X.D.Wang, Investigation of Ir-modified carbon felt as the positive electrode of an all-vanadium redox flow battery, Electrochimica Acta 52 (2007) 6755-6762 [6] Xing Xie, Meng Ye, Liangbing Hu, Nian Liu, James R. McDonough, Wei Chen, H. N. Alshareef, Craig S. Criddle, Yi Cui, Carbon nanotube-coated macroporous sponge for microbial fule cell electrode, The Royal Society of Chemistry Energy Environ. Sci. 5 (2012) 5265-5270 [7] Na Zhao, Zhaokun Ma, Huaihe Song, Yangen Xie, Man Zhang, Enhancement of bioelectricity generation by synergistic modification of vertical carbon nanotubes/polypyrrole for the carbon fibers anode in microbial fuel cell, Electrochimica Acta 296 (2019) 69-74 [8] Zhisheng Lv, Daohai Xie, Xianjun Yue, Chunhua Feng, Chaohai Wei, Ruthenium oxidecoated carbon felt electrode : A highly active anode for microbial fuel cell applications, Journal of Power Sources, 210 (2012) 26-31 [9] John Mcdonalad-Wharry, Merilyn Manly-Harris, Kim pickering, Carbonisation of biomass-derived chars and the thermal reduction of a graphene oxide sample studied using Raman spectroscopy, Carbon 59 (2013) 383-405 [10] DongRak Sohn, Jong Wan KO, Eun Jin Son, Sung Hyun Ko, Tae-Hee Kim, HyukSang Kwon, Chan Beum Park, Cellulos-Templated, Dual-Carbonized Na3V2(PO4)3 for Energy Storage with High Rate Capability, ChemElectroChem 5 (2018) 2186-2191 6
[11] Fang Zhao, Andrei Vrajitoarea, Qi Jiang, Xiaoyu Han, Aysha Chaudhary, Joseph O. Welch , Richard B. Jackman, Graphene-Nanodiamond Heterostructures and their application to High Current Device, Nature Scientific Reports 5 (2015) 13771 [12] Yunming Li, Shuyin Xu, Xiaoyan Wu, Juezhi Yu, Yuesheng Wang, Yong-Sheng Hu, Hong Li, Liquan Chen and Xuejie Huang, Amorphous monodispersed hard carbon microspherules derived from biomass as a high performance negative electrode material for sodium-ion batteries, Royal Society of Chemistry J. Mater. Chem. A, 3 (2015) 71-77
7
Highlights ○ A volume-porous electrode is to carbonize a close packing of phenolic resin spheres. ○ Liquid or gas fluid flow is allowed through the pore spaces of the electrode. ○ Well-controlled and uniformly-distributed pores of triangle-shape are comprised. ○ A amorphous carbon of high purity above 99.9% is formed. ○ High porosity of about 37% and high conductivity above 5.05 Scm-1 are resulted. .
8