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Fabrication of porous SiC(y) (core)/C (shell) fibres using a hybrid precursor of polycarbosilane and pitch

Fabrication of porous SiC(y) (core)/C (shell) fibres using a hybrid precursor of polycarbosilane and pitch
Fabrication of porous SiC(y) (core)/C (shell) fibres using a hybrid precursor of polycarbosilane and pitch
Porous SiCy (core)/C (shell) composite fibres have been fabricated using a simple KOH controlled-activation of SiCx fibres, which were pyrolyzed from polycarbosilane-pitch blend fibres. Effects of activation conditions and pyrolysis temperatures were studied. There are distinctive interfaces observed on the cross-sections of the co-axial fibres, where Si content varies gradually from the core to the shell. The etching of Si follows a slow “core-reducing” process in N2, while in CO2, cracks are frequently observed on the shells due to the accelerated activations. V-shaped Si-free carbon fibres could be obtained when a lower pyrolysis temperature was used to produce the SiCx fibres.

Microporous carbon (MC)-based materials have received intensive attention in the context of physisorption for hydrogen storage in the coming era of hydrogen economy [1]. Recently, tremendous efforts have been made to prepare MCs with high specific surface areas (SSAs) and developed porosity, typically, high SSAs can be achieved by controlled-activation of carbon precursors [3], template-assembling using Zeolites [2], or metal-extracting from carbides (carbide-derived carbons, CDCs) [4]. All these candidates have shown brilliant future for the hydrogen storage. However, the amounts of hydrogen adsorbed are still quite limited under high pressure and ambient temperature conditions [5]. Fortunately, the modification of C surfaces through incorporation of functional groups or dopants facilitates increasing binding energy of hydrogen with MCs and most recently, B-substituted MC has been synthesized and exhibited increased H2 storage capacity, 3.2 wt.%, almost double that of MC with similar SSA [6]. As simulated [7], Si should be a good alternative dopant due to the much higher binding energy of hydrogen with SiC. However, SiC usually has low SSA and hard to fabricate porous structure. We here reported a simple one-step activation to produce porous SiC fibres using a hybrid precursor of polycarbosilane (PCS) and pitch. Interestingly, novel core–shell structured materials were obtained. The influences of processing parameters on the cross-section morphologies were discussed in this letter.Polycarbosilane and pitch were mixed with a weight ratio of 55%/45%, melt-spun into green fibres, cured in air and pyrolyzed in N2 giving C-rich SiCx fibres. Then the SiCx fibres were loaded with KOH at a definite impregnation mass ratio (R = wt. KOH/wt. fibres), and activated in N2 or CO2 at a defined temperature/duration (for experimental details, see Supplementary information).



0008-6223
2115-2118
Chu, Zengyong
150eda25-e547-43c4-a047-206d11a01bcf
He, Rongan
d0e2f08e-6739-4355-aded-2142eb25e899
Zhang, Xiaobin
250668b7-bb5d-41a8-8f04-414d4d575a06
Jiang, Zheng
bcf19e78-f5c3-48e6-802b-fe77bd12deab
Cheng, Haifeng
1439d1a7-5ae4-4b94-803e-715783f55f04
Wang, Yingde
5ba2ce9d-8eee-4c68-854c-e498b00bb6cf
Li, Xiaodong
9a1d146e-1c0d-4b78-b84e-7706504a1cdc
Chu, Zengyong
150eda25-e547-43c4-a047-206d11a01bcf
He, Rongan
d0e2f08e-6739-4355-aded-2142eb25e899
Zhang, Xiaobin
250668b7-bb5d-41a8-8f04-414d4d575a06
Jiang, Zheng
bcf19e78-f5c3-48e6-802b-fe77bd12deab
Cheng, Haifeng
1439d1a7-5ae4-4b94-803e-715783f55f04
Wang, Yingde
5ba2ce9d-8eee-4c68-854c-e498b00bb6cf
Li, Xiaodong
9a1d146e-1c0d-4b78-b84e-7706504a1cdc

Chu, Zengyong, He, Rongan, Zhang, Xiaobin, Jiang, Zheng, Cheng, Haifeng, Wang, Yingde and Li, Xiaodong (2010) Fabrication of porous SiC(y) (core)/C (shell) fibres using a hybrid precursor of polycarbosilane and pitch. Carbon, 48 (7), 2115-2118. (doi:10.1016/j.carbon.2010.01.064).

Record type: Article

Abstract

Porous SiCy (core)/C (shell) composite fibres have been fabricated using a simple KOH controlled-activation of SiCx fibres, which were pyrolyzed from polycarbosilane-pitch blend fibres. Effects of activation conditions and pyrolysis temperatures were studied. There are distinctive interfaces observed on the cross-sections of the co-axial fibres, where Si content varies gradually from the core to the shell. The etching of Si follows a slow “core-reducing” process in N2, while in CO2, cracks are frequently observed on the shells due to the accelerated activations. V-shaped Si-free carbon fibres could be obtained when a lower pyrolysis temperature was used to produce the SiCx fibres.

Microporous carbon (MC)-based materials have received intensive attention in the context of physisorption for hydrogen storage in the coming era of hydrogen economy [1]. Recently, tremendous efforts have been made to prepare MCs with high specific surface areas (SSAs) and developed porosity, typically, high SSAs can be achieved by controlled-activation of carbon precursors [3], template-assembling using Zeolites [2], or metal-extracting from carbides (carbide-derived carbons, CDCs) [4]. All these candidates have shown brilliant future for the hydrogen storage. However, the amounts of hydrogen adsorbed are still quite limited under high pressure and ambient temperature conditions [5]. Fortunately, the modification of C surfaces through incorporation of functional groups or dopants facilitates increasing binding energy of hydrogen with MCs and most recently, B-substituted MC has been synthesized and exhibited increased H2 storage capacity, 3.2 wt.%, almost double that of MC with similar SSA [6]. As simulated [7], Si should be a good alternative dopant due to the much higher binding energy of hydrogen with SiC. However, SiC usually has low SSA and hard to fabricate porous structure. We here reported a simple one-step activation to produce porous SiC fibres using a hybrid precursor of polycarbosilane (PCS) and pitch. Interestingly, novel core–shell structured materials were obtained. The influences of processing parameters on the cross-section morphologies were discussed in this letter.Polycarbosilane and pitch were mixed with a weight ratio of 55%/45%, melt-spun into green fibres, cured in air and pyrolyzed in N2 giving C-rich SiCx fibres. Then the SiCx fibres were loaded with KOH at a definite impregnation mass ratio (R = wt. KOH/wt. fibres), and activated in N2 or CO2 at a defined temperature/duration (for experimental details, see Supplementary information).



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Published date: June 2010
Organisations: Faculty of Engineering and the Environment

Identifiers

Local EPrints ID: 352769
URI: http://eprints.soton.ac.uk/id/eprint/352769
ISSN: 0008-6223
PURE UUID: ecb6e6d5-6973-4c10-ae65-62245e0c9659
ORCID for Zheng Jiang: ORCID iD orcid.org/0000-0002-7972-6175

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Date deposited: 20 May 2013 15:19
Last modified: 03 Dec 2019 01:36

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Contributors

Author: Zengyong Chu
Author: Rongan He
Author: Xiaobin Zhang
Author: Zheng Jiang ORCID iD
Author: Haifeng Cheng
Author: Yingde Wang
Author: Xiaodong Li

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