Ion Dynamics at the Single Wall Carbon Nanotube Based Composite Electrode/Electrolyte Interface: Influence of the Cation Size and the Electrolyte pH

Journal:  J. Phys. Chem. C

Authors:  Freddy Escobar-Teran, Hubert Perrot, and Ozlem Sel

Abstract: Electrochemical quartz crystal microbalance (EQCM) and ac-electrogravimetry methods were employed to study ion dynamics in single wall carbon nanotube (SWCNT) based electrodes in various aqueous electrolytes and different electrolyte pH. The pH dependence of the electroadsorption phenomena studied in NaCl at pH 2, pH 7 and pH 10 indicated that low and high pH values amplify the anion and cation contribution, respectively; which means that in the same potential range, the pH of the aqueous electrolyte is adjustable to preferentially electroadsorb cations or anions. The cation size dependence of the electrodeposition phenomena was also studied by changing the electrolyte cation from Li+, Na+ to K+. The results indicated that Li+ and Na+ species are more tightly bonded to their water molecules in their hydration shell compared to the potassium species, i.e. dehydration of K+ is easier than that of Na+ and Li+. K+ ions due their completely dehydrated state, probably become equivalent to partially dehydrated Na+.nH2O, in terms of kinetics. Li+.nH2O ions dynamics is slower since it is much more difficult for them to get rid of their hydration shell making their transfer the slowest among the other cations. Our electrogravimetric results clearly indicate that the dehydration affinity and the ions size play a role in the electroadsorption dynamics of the species on the SWCNT based composite electrodes.

Keywords: Electrochemical Quartz crystal microbalance, carbon nanotube electrodes, aqueous electrolytes ,