Accelerated electron-transfer reaction of the O2/O2- redox couple on multi-walled carbon nanotubes -: Modified edge-plane pyrolytic graphite electrode in room-temperature ionic liquids

An electrocatalysis of the multi-walled carbon nanotubes (MWCNTs)/Nafion-modified edge-plane pyrolytic graphite (EPPG) electrode for the one-electron reduction-oxidation reaction of the O-2/O-2(-) (superoxide ion) redox couple in three 1-n-alkyl-3-methylimidazolium tetrafluoroborate room temperature ionic liquids (RTILs), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4), 1-n-propyl-3-methylimidazolium tetrafluoroborate (PMTBF4) and 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4) has been found. We have observed that in all the RTILs both the cathodic and anodic peak currents and the peak potential separations (Delta E-p) between the anodic and cathodic peak potentials at the MWCNTs/Nafion-modified electrode are increased and decreased, respectively, compared with those at the bare electrode. The values of the standard rate constant (k(0)) were estimated from the Delta E-p values. i.e., the k(0) values at the MWCNTs/Nafion-modified electrode are (8.3 +/- 0.1) x 10(-3), (10.4 +/- 0.1) x 10(-3) and (4.2 +/- 0.1) x 10(-3) cm s(-1) in EMIBF4, PMIBF4 and BMIBF4, respectively, while the corresponding values at the bare electrode are (4.3 +/- 0.1) x 10(-3), (2.9 +/- 0.1) x 10(-3) and (2.3 +/- 0.1) x 10(-3) cm s(-1), respectively. The observed enhancement of the O-2/O-2 redox reaction is discussed briefly based on the catalytic effects and physicochemical properties of carbon nanotubes.