Effect of oxygen functionalisation on the electrochemical behaviour of multiwall carbon nanotubes for alcohol oxidation reactions

Abstract

Multiwall carbon nanotubes (MWCNTs) have been popularly used as catalyst supports for various electrochemical devices and reactions. In their preparation, surface oxidation by chemical oxidants is often necessary to purify MWNCTs, which also results in the formation of oxygen functional groups. However, the effect of these functionalities on electrochemical behavior of MWCNTs for alcohol oxidations remain largely unknown. In this study, we show that surface oxidation activates MWCNTs for electrochemical oxidation of alcohols in alkaline media (0.1 M KOH). Significantly enhanced catalytic activity in terms of higher current density (j) as well as lower alcohol oxidation onset potentials was observed following controlled oxidations via chemical or electrochemical methods. High-resolution XPS analysis suggests that the surface bound oxygen functionalities e.g. ketonic group (CO) contribute primarily to the observed increase in catalytic performance. Moreover, to further increase the activity of MWCNTs, hydrothermal treatment was applied to repair the structural damage induced by the harsh oxidation treatment without the sacrifice of oxygen functional groups. Using the hydrothermally treated, surface-oxidized MWCNTs, EtOH undergoes oxidation into acetic acid with ∼99% faradaic efficiency. This study reveals the unique role of oxygen functional groups on MWCNTs towards catalytic alcohol oxidations for possible applications in direct alcohol fuel cells and alcohol sensors.