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From Soybean residue to advanced supercapacitors.

Ferrero GA, Fuertes AB, Sevilla M - Sci Rep (2015)

Bottom Line: Supercapacitor technology is an extremely timely area of research with fierce international competition to develop cost-effective, environmentally friendlier EC electrode materials that have real world application.Interestingly, when Li2SO4 is used, the voltage window is extended up to 1.7 V (in contrast to 1.1 V in H2SO4).Thus, the amount of energy stored is increased by 50% compared to H2SO4 electrolyte, enabling this environmentally sound Li2SO4-based supercapacitor to deliver ~12 Wh kg(-1) at a high power density of ~2 kW kg(-1).

View Article: PubMed Central - PubMed

Affiliation: Instituto Nacional del Carbón (CSIC), P.O. Box 73, Oviedo 33080, Spain.

ABSTRACT
Supercapacitor technology is an extremely timely area of research with fierce international competition to develop cost-effective, environmentally friendlier EC electrode materials that have real world application. Herein, nitrogen-doped carbons with large specific surface area, optimized micropore structure and surface chemistry have been prepared by means of an environmentally sound hydrothermal carbonization process using defatted soybean (i.e., Soybean meal), a widely available and cost-effective protein-rich biomass, as precursor followed by a chemical activation step. When tested as supercapacitor electrodes in aqueous electrolytes (i.e. H2SO4 and Li2SO4), they demonstrate excellent capacitive performance and robustness, with high values of specific capacitance in both gravimetric (250-260 and 176 F g(-1) in H2SO4 and Li2SO4 respectively) and volumetric (150-210 and 102 F cm(-3) in H2SO4 and Li2SO4 respectively) units, and remarkable rate capability (>60% capacitance retention at 20 A g(-1) in both media). Interestingly, when Li2SO4 is used, the voltage window is extended up to 1.7 V (in contrast to 1.1 V in H2SO4). Thus, the amount of energy stored is increased by 50% compared to H2SO4 electrolyte, enabling this environmentally sound Li2SO4-based supercapacitor to deliver ~12 Wh kg(-1) at a high power density of ~2 kW kg(-1).

No MeSH data available.


(a) Nyquist plot and (b) frequency response for the N-doped porous carbons. Electrolyte: 1 M H2SO4.
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f4: (a) Nyquist plot and (b) frequency response for the N-doped porous carbons. Electrolyte: 1 M H2SO4.

Mentions: Because of the microporous nature of these materials and the abundance of nitrogen and oxygen functionalities, their capacitive behavior was tested in aqueous electrolytes, i.e. H2SO4 and Li2SO4. Figure 4 shows the results obtained from EIS measurements for 1 M H2SO4 electrolyte. The Nyquist plots in Fig. 4a show a decrease in the equivalent series resistance (ESR) with the rise in synthesis temperature, in agreement with the enhancement of the electronic conductivity registered with the rise in synthesis temperature (from 6·10−3 S cm−1 at 600 °C up to 2.5 S cm−1 at 800 °C, Table 1). Furthermore, a clear semicircle associated with charge transfer processes is detected in AS-600 and AS-650, indicating the presence of pseudocapacitance phenomena contributed by the nitrogen and oxygen functionalities. Similarly, a small semicircle is registered in AS-700 as can be seen in the inset of Fig. 4a. This feature is lacking in AS-800, suggesting the absence of pseudocapacitance phenomena. These results are in agreement with the cyclic voltammograms (CV) in Supplementary Fig. S3 online. Thus, the CV curves corresponding to the materials synthesized at T ≤ 700 °C are quasi-rectangular, with a clear faradaic hump at cell voltages < 0.4–0.5 V (a detailed analysis of the behavior of the positive and negative electrodes in the supercapacitor can be found in the Supporting Information in Supplementary Fig. S4 online). In contrast, sample AS-800 shows a rectangular shape typical of an electrochemical double-layer capacitor (see Supplementary Fig. S3d online). The variation of the normalized capacitance with frequency is represented in Fig. 4b. A faster frequency response can be clearly seen with the increase in activation temperature. Accordingly, AS-800 and AS-700 have small relaxation time constants of 1.4 s and 1.6 s respectively, which are considerably smaller values than those of the samples synthesized at lower temperatures (i.e. 8.0 s for AS-650 and 8.6 s for AS-600). The diminution of the relaxation time constant with the rise in activation temperature can be ascribed to: i) better ion transport characteristics owing to the development of a second micropore system centered at 1.1 nm; ii) an enhancement of the electronic conductivity (see Table 1), iii) the removal of oxygen functionalities which may interact with the ion solvated shells, slowing down the motion of ions3839, and iv) the diminishing impact of slow redox reactions (pseudocapacitance). Consequently, the rate performance increases with the activation temperature, which is confirmed by the CV curves in Supplementary Fig. S3 online. Indeed, in the case of AS-800 and AS-700 the CV shape is maintained up to 200 mV s−1 with a good capacitance retention (72% for AS-800 and 62% for AS-700). On the other hand, AS-650 and AS-600 are only able to work up to 50 mV s−1 and they display a lower capacitance retention (~64%).


From Soybean residue to advanced supercapacitors.

Ferrero GA, Fuertes AB, Sevilla M - Sci Rep (2015)

(a) Nyquist plot and (b) frequency response for the N-doped porous carbons. Electrolyte: 1 M H2SO4.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4645100&req=5

f4: (a) Nyquist plot and (b) frequency response for the N-doped porous carbons. Electrolyte: 1 M H2SO4.
Mentions: Because of the microporous nature of these materials and the abundance of nitrogen and oxygen functionalities, their capacitive behavior was tested in aqueous electrolytes, i.e. H2SO4 and Li2SO4. Figure 4 shows the results obtained from EIS measurements for 1 M H2SO4 electrolyte. The Nyquist plots in Fig. 4a show a decrease in the equivalent series resistance (ESR) with the rise in synthesis temperature, in agreement with the enhancement of the electronic conductivity registered with the rise in synthesis temperature (from 6·10−3 S cm−1 at 600 °C up to 2.5 S cm−1 at 800 °C, Table 1). Furthermore, a clear semicircle associated with charge transfer processes is detected in AS-600 and AS-650, indicating the presence of pseudocapacitance phenomena contributed by the nitrogen and oxygen functionalities. Similarly, a small semicircle is registered in AS-700 as can be seen in the inset of Fig. 4a. This feature is lacking in AS-800, suggesting the absence of pseudocapacitance phenomena. These results are in agreement with the cyclic voltammograms (CV) in Supplementary Fig. S3 online. Thus, the CV curves corresponding to the materials synthesized at T ≤ 700 °C are quasi-rectangular, with a clear faradaic hump at cell voltages < 0.4–0.5 V (a detailed analysis of the behavior of the positive and negative electrodes in the supercapacitor can be found in the Supporting Information in Supplementary Fig. S4 online). In contrast, sample AS-800 shows a rectangular shape typical of an electrochemical double-layer capacitor (see Supplementary Fig. S3d online). The variation of the normalized capacitance with frequency is represented in Fig. 4b. A faster frequency response can be clearly seen with the increase in activation temperature. Accordingly, AS-800 and AS-700 have small relaxation time constants of 1.4 s and 1.6 s respectively, which are considerably smaller values than those of the samples synthesized at lower temperatures (i.e. 8.0 s for AS-650 and 8.6 s for AS-600). The diminution of the relaxation time constant with the rise in activation temperature can be ascribed to: i) better ion transport characteristics owing to the development of a second micropore system centered at 1.1 nm; ii) an enhancement of the electronic conductivity (see Table 1), iii) the removal of oxygen functionalities which may interact with the ion solvated shells, slowing down the motion of ions3839, and iv) the diminishing impact of slow redox reactions (pseudocapacitance). Consequently, the rate performance increases with the activation temperature, which is confirmed by the CV curves in Supplementary Fig. S3 online. Indeed, in the case of AS-800 and AS-700 the CV shape is maintained up to 200 mV s−1 with a good capacitance retention (72% for AS-800 and 62% for AS-700). On the other hand, AS-650 and AS-600 are only able to work up to 50 mV s−1 and they display a lower capacitance retention (~64%).

Bottom Line: Supercapacitor technology is an extremely timely area of research with fierce international competition to develop cost-effective, environmentally friendlier EC electrode materials that have real world application.Interestingly, when Li2SO4 is used, the voltage window is extended up to 1.7 V (in contrast to 1.1 V in H2SO4).Thus, the amount of energy stored is increased by 50% compared to H2SO4 electrolyte, enabling this environmentally sound Li2SO4-based supercapacitor to deliver ~12 Wh kg(-1) at a high power density of ~2 kW kg(-1).

View Article: PubMed Central - PubMed

Affiliation: Instituto Nacional del Carbón (CSIC), P.O. Box 73, Oviedo 33080, Spain.

ABSTRACT
Supercapacitor technology is an extremely timely area of research with fierce international competition to develop cost-effective, environmentally friendlier EC electrode materials that have real world application. Herein, nitrogen-doped carbons with large specific surface area, optimized micropore structure and surface chemistry have been prepared by means of an environmentally sound hydrothermal carbonization process using defatted soybean (i.e., Soybean meal), a widely available and cost-effective protein-rich biomass, as precursor followed by a chemical activation step. When tested as supercapacitor electrodes in aqueous electrolytes (i.e. H2SO4 and Li2SO4), they demonstrate excellent capacitive performance and robustness, with high values of specific capacitance in both gravimetric (250-260 and 176 F g(-1) in H2SO4 and Li2SO4 respectively) and volumetric (150-210 and 102 F cm(-3) in H2SO4 and Li2SO4 respectively) units, and remarkable rate capability (>60% capacitance retention at 20 A g(-1) in both media). Interestingly, when Li2SO4 is used, the voltage window is extended up to 1.7 V (in contrast to 1.1 V in H2SO4). Thus, the amount of energy stored is increased by 50% compared to H2SO4 electrolyte, enabling this environmentally sound Li2SO4-based supercapacitor to deliver ~12 Wh kg(-1) at a high power density of ~2 kW kg(-1).

No MeSH data available.