The electrocatalysis of multi-walled carbon nanotubes (MWCNTs) for oxygen reduction reaction (ORR) in room temperature ionic liquids (RTILs)

Abstract

Oxygen reduction reaction (ORR) was investigated on a multi-walled carbon nanotubes (MWCNTs)-modified edge plane pyrolytic graphite (EPPG) electrode using cyclic voltammetry (CV) in three kinds of room temperature ionic liquids (RTILs), i.e., 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4), 1-n-propyl-3-methylimidazolium tetrafluoroborate (PMIBF4), and 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4). The results demonstrated that, after being modified by MWCNTs on the EPPG electrode, both the reduction peak current of oxygen and the oxidation peak current of superoxide anion were all dramatically increased, and the values of standard rate constant, Ks, corresponding to ORR, were greatly enhanced. Under the same condition, in PMIBF4, MWCNTs-modified EPPG electrode exhibited the most satisfied electrocatalysis for ORR, in which standard rate constant, ks, was improved from 2.9 × 10-3 cm s-1 on a EPPG electrode, to 10.4 × 10-3 cm s-1. While in EMIBF4 and BMIBF4, after being modified by MWCNTs, the value of _s was increased from 4.3 × 10-3 to 8.3 × 10-3 and 2.3 × 10-3 to 4.2 × 10-3 cm s-1, respectively. For the catalysis of MWCNTsmodified EPPG electrode towards ORR, the enhanced surface area of electrode and the increased amount of "defect" sites on electrode were thought to be the main reasons for our obtained results.