The role of the electric conductivity of carbons in the electrochemical capacitor performance

• Published in: Journal of electroanalytical chemistry (Lausanne, Switzerland) Vol. 657; no. 1; pp. 176 - 180
• Main Authors: Sánchez-González, José, Stoeckli, Fritz, Centeno, Teresa A.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 01-07-2011; Elsevier
• Subjects: Activated carbon; Applied sciences; Capacitors. Resistors. Filters; carbon; Electric conductivity; electrical conductivity; Electrical engineering. Electrical power engineering; Electrochemical capacitor; electrochemistry; electrolytes; Exact sciences and technology; Heat-treatment; oxygen; sulfuric acid; temperature; Various equipment and components; Activated carbon; Electrochemical capacitor; Heat-treatment; Electric conductivity; Heat treatment; Electrical conductivity; Electrolytic capacitor; Electrode material; Carbon; Acidic solution; Sulfuric acid; Organic solvent; Medium effect; Acetonitrile; Supercapacitor; Aqueous solution
• DOI: 10.1016/j.jelechem.2011.03.025
• EISSN: 1873-2569
• ISSN: 1572-6657

► Poor suitability of a carbon for supercapacitor is overcome by heating at 700–900°C. ► Carbon-supercapacitor performance should not be analised only on pores suitability. ► Supercapacitor performance of carbons greatly depends on their electric properties.
The interpretation of the performance of electrochemical capacitors based exclusively on the textural features and surface chemistry of carbons can be insufficient, or even misleading, in the case of materials prepared at low temperatures (typically below 800
°C).
It is suggested that the gradual improvement of the electrochemical performances of carbon-based capacitors at high current densities, following heat treatments up to 900
°C, is mainly a consequence of the simultaneous increase in conductivity. This is illustrated by a study of carbons based on a mesoporous carbon prepared at 550
°C, which displays poor electrochemical performances and a low conductivity (4.6 × 10
−6
S m
−1). A first heat treatment at 700
°C leads to major structural, chemical and electrochemical changes, due to the collapse of the smaller mesopores and the formation of a microporous structure with average pore widths around 1.3
nm. One also observes a reduction in the surface oxygen density from 13 to approximately 5
μmol
m
−2. Further heat treatments at 800 and 900
°C do not modify significantly these characteristics, nor the surface-related capacitances at low current densities (1
mA
cm
−2) in the aqueous (2
M H
2SO
4) and organic (1
M (C
2H
5)
4NBF
4/CH
3CN) electrolytes. On the other hand, one observes increasingly high rate capabilities which may be ascribed to the simultaneous increase in conductivity from 7.3 to 147.8
S m
−1 between 700 and 900
°C.