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SYNTHESIS OF CARBON GELS BY SOL-GEL POLYMERIZATION OF COAL-DERIVED PHENOLIC OILS WITH FORMALDEHYDE

Abstract : Introduction Phenolic oils (PO) are low-value coal-derived liquids obtained from the distillation of coal tar. As they are rich in phenol, PO are a priori very interesting precursors for preparing low-cost carbon gels based on sol-gel phenol-formaldehyde polymerization routes. Synthesis of carbon gels from PO and their application as electrode materials for supercapacitors would constitute an important step towards the valorization of those liquids. However, the main difficulty to overcome is that PO has a multi-component nature, with many aromatic compounds and heterocycles of different reactivity. In this study, we synthesized porous carbon gels obtained by sol-gel polymerization of PO (∼ 25 wt.% of phenol) with formaldehyde, using different solvents in either acidic or basic media. The porous texture of the carbons was further developed by KOH activation, and the resultant activated carbons were tested as supercapacitor electrodes. The physicochemical properties of the carbon materials were correlated to the electrochemical performances of the carbon electrodes. Materials and Methods Synthesis of activated carbons (ACs) from xerogels: Two types of xerogels were prepared from: 1) 2.36 g PO, 2.36 g formaldehyde (F), 2.5 g n-propanol and 0.23 g NaOH; or 2) 15 g PO, 3.123 g para-formaldehyde (pF), 12.5 g i-propanol and 0.64 g p-toluenesulfonic acid (pTSA). Both reaction mixtures were put into sealed glass flasks and heated at 85°C for 5-7days. The resultant alcogels were dried in an oven at 85°C to obtain xerogels, which were ground and chemically activated at 750°C during 1h in nitrogen atmosphere with different KOH/xerogel ratios, w= 2 to 5. The ACs were repeatedly washed with 1M HCl and subsequently with distilled water until free of chloride ions. Finally, they were dried at 105 °C for 12 h and labelled in each case: 1) CXw, where w is the KOH / xerogel mass ratio (CX0 carbon xerogel, where w = 0, was obtained by carbonization of the organic xerogel at 900°C for 1h); 2) Wi, where i = 0, 3, 4 and 5. Commercial ACs, MSC-20X and MSC-30X, were also used for comparison. Electrochemical characterisation: carbon electrodes were prepared by spreading a paste (∼ 3 mg) containing the AC, polytetrafluoroethylene (PTFE) and carbon black (85:10:5 wt.%) onto graphite foils, and were subsequently impregnated with 2 mol L-1 H2SO4 for 72 h. Cyclic voltammetry (CV) tests were performed in a three-electrode cell within the potential window of 0-0.74 V, using a platinum gauze as counter electrode and a saturated calomel electrode (SCE) as reference. Galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) tests were carried out in a two-electrode cell by placing two identical electrodes (∼ 3 mg per electrode) separated by a glass fiber disc between two gold current collectors. Results and Discussion Chemical activation greatly developed the porous texture of the xerogels by mainly creating micropores. Micropore volumes, Vµ-NLDFT, were considerably higher than mesopore volumes, VM, and the main pore size, L0, of the ACs was < 2 nm, thus indicating that their porous textures were essentially microporous (Table 1). Given that the BET method overestimates the surface areas (ABET) of highly microporous ACs, the values obtained from the pore size distributions (PSDs), SNLDFT, should be preferred [1]. SNLDFT of MSC30X was 2394 m 2 g-1 , considerably lower than the overestimated ABET value of 3305 m 2 g-1. Among the ACs, W3 exhibited the most developed porous texture, having a SNLDFT of 2224 m 2 g-1. CX3 exhibited the highest SNLDFT of the CXw series, 2041 m 2 g-1 , and possessed the highest Vµ-NLDFT with diameters of 0.7 − 2 nm, which contributed in a greater extent to the SNLDFT.
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https://hal.univ-lorraine.fr/hal-02907625
Contributor : Maria Vanessa Fierro Pastor <>
Submitted on : Tuesday, January 5, 2021 - 3:59:33 PM
Last modification on : Wednesday, January 6, 2021 - 3:38:13 AM

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  • HAL Id : hal-02907625, version 1

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Angela Sanchez-Sanchez, María Izquierdo, Sébastien Schaeffer, Alain Celzard, Vanessa Fierro. SYNTHESIS OF CARBON GELS BY SOL-GEL POLYMERIZATION OF COAL-DERIVED PHENOLIC OILS WITH FORMALDEHYDE. Carbon 2018, Jul 2018, Madrid, Spain. ⟨hal-02907625⟩

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