Electrochemical Behavior of Highly Conductive Boron‐Doped Diamond Electrodes for Oxygen Reduction in Acid Solution

The electrochemical behavior of highly conductive, boron‐doped polycrystalline diamond thin films for oxygen reduction was examined in 0.5 M using linear sweep voltammetry. When the potential sweep is confined to the region negative of 0.0 V vs. Ag/AgCl, oxygen reduction is highly inhibited with cathodic current being observed at ∼ −0.6 V vs. Ag/AgCl, as compared with the standard potential for the two‐electron reduction of oxygen vs. Ag/AgCl at pH 0). The extreme inhibition of oxygen reduction may be due to an absence of catalytic sites. When the potential is swept to potentials positive of + 1.4 V vs. Ag/AgCl, the subsequent sweep into the negative region shows a reduction peak due to oxygen reduction. In this case, catalytic oxygen‐containing functional groups can be formed on carbon impurities. Relatively mild conditions are required to deactivate the catalytic functional groups, but strong oxidative treatment in base appears to substantially remove the carbon impurities. The oxygen reduction behavior in acid solution could be useful in characterizing diamond electrodes, i.e., as a diagnostic for the presence of carbon on chemical‐vapor‐deposited diamond thin‐film electrodes. It is proposed that diamond electrode surfaces free of carbon are highly insensitive to oxygen, which could be a useful feature in electroanalysis. © 1999 The Electrochemical Society. All rights reserved.