Steric effects in adsorption of ions from mixed electrolytes into microporous carbon

• Published in: Electrochemistry communications Vol. 15; no. 1; pp. 63 - 65
• Main Authors: Segalini, Julie, Iwama, Etsuro, Taberna, Pierre-Louis, Gogotsi, Yury, Simon, Patrice
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01.02.2012; Amsterdam Elsevier; New York, NY
• Subjects: Applied sciences; Capacitors. Resistors. Filters; Electrical engineering. Electrical power engineering; Electrochemical double-layer capacitor; Engineering Sciences; Exact sciences and technology; Ion adsorption; Materials; Microporous carbon; Mixed electrolytes; Steric effect; Various equipment and components; Electrochemical double-layer capacitor; Mixed electrolytes; Ion adsorption; Steric effect; Microporous carbon; Charge storage; Ions; Electrolytic capacitor; Carbon; Porous material; Ionic liquid; Organic solvent; Microporosity; Adsorption; Electrolyte; Acetonitrile; Supercapacitor; Physicochemical properties
• ISSN: 1388-2481; 1873-1902
• DOI: 10.1016/j.elecom.2011.11.023

With the goal to improve the capacitance in electrochemical double-layer capacitors (EDLCs) many studies on pore size/ion size relationship have been undertaken to achieve a better understanding of the charge storage mechanism in the electrochemical double-layer in confinement. A significant capacitance increase was achieved by using carbon electrodes with micropores (< 1 nm), when the carbon pore size was close to the ion size. In this paper, the accessibility of narrow pores is investigated by selecting a carbon with a small pore size (< 0.7 nm) and electrolyte mixtures with different ion sizes. It has been shown that the adsorption capacitance limitation observed for large cations and anions could be overcome by adding ions with a smaller effective size. This result demonstrates that the pores are accessible when their size matches the effective ion size and contradicts the surface saturation assumption; effective ion size which exceeds the pore size leads to current limitation. This work confirms that the steric effect is involved when ions are adsorbed into pores and highlights the importance of controlling ion size/pore size relationship for optimisation of the capacitive performance of EDLC devices. ► Electrolyte mixtures enable to study ion size/pore size relationship. ► Capacitance limitation is observed if the pore size is below the effective ion size. ► No charge saturation, capacitance limitation is only due to a steric effect.