Threshold effect of admixtures of platinum on the electrochemical activity of amorphous diamond-like carbon thin films

The kinetics of electrode reactions in a Fe(CN)(6)(3-/4-) redox system on thin-film electrodes of amorphous diamond-like carbon with admixtures of platinum (0-15 at.%) have been studied. The wide-gap diamond-like carbon is not in itself electrochemically active; however, it acquires electrochemical activity upon introducing platinum into the DLC bulk during the film deposition. The effect of platinum is shown to be of a threshold nature: the electrochemical current appears at approximately 3 at.% and saturates at approximately 10 at.% of Pt. By contrast, the differential capacitance increases continuously with increasing Pt content; and the DLC resistivity practically does not change. The observed effects are explained in terms of a model assuming a non-uniform character of both electric conductance in the DLC bulk and the catalytic effect of platinum at the electrode/solution interface. (C) 2002 Elsevier Science B.V. All rights reserved.