Oxygen reduction reaction on covalently and noncovalently modified carbon nanowalls

Abstract

An effect of highly oriented carbon nanowalls modification on oxygen reduction reaction was studied by means of a rotating disk electrode. Namely nanowalls were modified with oxygencontaining functional groups. Moreover, an adsorption of borneol (a surfactant with twodimensional structure) was considered. Two distinct waves are observed on voltammograms in aerated alkaline solutions that points out to the two-step process of oxygen reduction with the formation of H2O2 as intermediate. Both types of surface modification were found to affect substantially the absolute currents of the waves as well as their ratio. This effect was assumed to be caused by the topology peculiarities of carbon nanowalls that determine the electrochemical heterogeneity of the electrode surface. For initial nanowalls, the process of two-step reduction takes place on the edges of nanowalls. A parallel channel of oxygen reduction with the formation of water is assumed to be realized on the defects of basal planes at high overvoltage. In the case of noncovalent modification, borneol is adsorbed mainly on basal planes of nanowalls and blocks substantially parallel reduction channel. After covalent modification, oxygen reduction proceeds mainly through a two-step channel as a result of the increase in the number of oxygen-containing functional groups (the centers of two-step reduction) on the edges of nanowalls.