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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.


Variation of specific capacitance and coulombic efficiency with increasing current density in 1 M Li2SO4, and (b) Ragone plot for the AS-800 sample in 1 M H2SO4 (Voltage range: 1.1 V) and 1 M Li2SO4 (Voltage range: 1.7 V).
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f8: Variation of specific capacitance and coulombic efficiency with increasing current density in 1 M Li2SO4, and (b) Ragone plot for the AS-800 sample in 1 M H2SO4 (Voltage range: 1.1 V) and 1 M Li2SO4 (Voltage range: 1.7 V).

Mentions: As for the H2SO4 electrolyte, the specific capacitance and rate capability of the supercapacitor in Li2SO4 was determined from constant current charge-discharge experiments. The variation in specific capacitance with increasing current density is displayed in Fig. 8a, along with the values of coulombic efficiency, which show ideal capacitive behavior regardless of the discharge rate. A specific capacitance of 176 F g−1 (102 F cm−3) is achieved at 0.2 A g−1, which is higher than that of commercial activated carbons in 1 M Li2SO4 electrolyte485054. Although this value is somewhat lower than that obtained in H2SO4 electrolyte (i.e. 258 F g−1), the fact that in Li2SO4 the EC system can operate at 1.7 V (vs. 1.1 V in 1 M H2SO4) is a clear advantage that compensates for the lower capacitance values relative to the amount of energy stored, as will be discussed below. Furthermore, AS-800 has a specific capacitance of ~130 F g−1 (75 F cm−3) at a relatively high current density of 10 A g−1, which implies a capacitance retention of 74%, a value still superior to that of other activated carbons found in the literature474855. This enhanced rate capability can be ascribed to the engineered surface chemistry and pore structure, which offer a smooth ion diffusion, coupled to a good electronic conductivity. The rate capability was further confirmed by electrochemical impedance spectroscopy (EIS) measurements. It was found that the microporous carbon material possesses a relaxation time constant close to 8 s, as can be deduced from the frequency response of capacitance in Supplementary Fig. S9a online. This value is considerably higher than that found in 1 M H2SO4 electrolyte, in agreement with the better rate capability recorded in 1 M H2SO4 compared to 1 M Li2SO4. On the basis of the EIS analysis, this difference in rate capability can be ascribed to the greater resistance of the supercapacitor (both ESR and EDR) in Li2SO4 than in H2SO4. Thus, ESR resistance increases from 0.17 Ohm in H2SO4 to 0.53 Ohm in Li2SO4, and EDR resistance (i.e. the resistance the electrolyte ions confront when they penetrate the porous structure) increases greatly from 0.17 Ohm in H2SO4 to 2.6 Ohm in Li2SO4 (see Supplementary Fig. S9b online). These EDR values are similar to those of other highly microporous biomass-based carbons, such as those derived from tobacco stems56, or sawdust/glucose-derived hydrochars49, but much higher than that of micro-mesoporous activated carbons (i.e. 0.5 Ohm)49, revealing hindered ion diffusion through the micropores in the case of the low conductive Li2SO4.


From Soybean residue to advanced supercapacitors.

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

Variation of specific capacitance and coulombic efficiency with increasing current density in 1 M Li2SO4, and (b) Ragone plot for the AS-800 sample in 1 M H2SO4 (Voltage range: 1.1 V) and 1 M Li2SO4 (Voltage range: 1.7 V).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f8: Variation of specific capacitance and coulombic efficiency with increasing current density in 1 M Li2SO4, and (b) Ragone plot for the AS-800 sample in 1 M H2SO4 (Voltage range: 1.1 V) and 1 M Li2SO4 (Voltage range: 1.7 V).
Mentions: As for the H2SO4 electrolyte, the specific capacitance and rate capability of the supercapacitor in Li2SO4 was determined from constant current charge-discharge experiments. The variation in specific capacitance with increasing current density is displayed in Fig. 8a, along with the values of coulombic efficiency, which show ideal capacitive behavior regardless of the discharge rate. A specific capacitance of 176 F g−1 (102 F cm−3) is achieved at 0.2 A g−1, which is higher than that of commercial activated carbons in 1 M Li2SO4 electrolyte485054. Although this value is somewhat lower than that obtained in H2SO4 electrolyte (i.e. 258 F g−1), the fact that in Li2SO4 the EC system can operate at 1.7 V (vs. 1.1 V in 1 M H2SO4) is a clear advantage that compensates for the lower capacitance values relative to the amount of energy stored, as will be discussed below. Furthermore, AS-800 has a specific capacitance of ~130 F g−1 (75 F cm−3) at a relatively high current density of 10 A g−1, which implies a capacitance retention of 74%, a value still superior to that of other activated carbons found in the literature474855. This enhanced rate capability can be ascribed to the engineered surface chemistry and pore structure, which offer a smooth ion diffusion, coupled to a good electronic conductivity. The rate capability was further confirmed by electrochemical impedance spectroscopy (EIS) measurements. It was found that the microporous carbon material possesses a relaxation time constant close to 8 s, as can be deduced from the frequency response of capacitance in Supplementary Fig. S9a online. This value is considerably higher than that found in 1 M H2SO4 electrolyte, in agreement with the better rate capability recorded in 1 M H2SO4 compared to 1 M Li2SO4. On the basis of the EIS analysis, this difference in rate capability can be ascribed to the greater resistance of the supercapacitor (both ESR and EDR) in Li2SO4 than in H2SO4. Thus, ESR resistance increases from 0.17 Ohm in H2SO4 to 0.53 Ohm in Li2SO4, and EDR resistance (i.e. the resistance the electrolyte ions confront when they penetrate the porous structure) increases greatly from 0.17 Ohm in H2SO4 to 2.6 Ohm in Li2SO4 (see Supplementary Fig. S9b online). These EDR values are similar to those of other highly microporous biomass-based carbons, such as those derived from tobacco stems56, or sawdust/glucose-derived hydrochars49, but much higher than that of micro-mesoporous activated carbons (i.e. 0.5 Ohm)49, revealing hindered ion diffusion through the micropores in the case of the low conductive Li2SO4.

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.