Boron-doped diamond electrodes, both as-grown and polarized anodically under different conditions, were prepd. in order to study the chem. and electrochem. changes of diamond and clarify the role played by the surface-state d. Many different treatments were employed: as-grown (BDDag), mildly polarized (BDDmild), strongly polarized in perchloric acid (BDDsevere), and strongly polarized in a sulfuric acid-acetic acid mixt. (BDDAcOH). Charge transfer processes at the electrode surface were studied by cyclic voltammetry. Simple electron transfer processes such as the outer-sphere redox system ferri/ferrocyanide (FeIII/II;(CN)6) and complex charge transfer reactions such as the inner-sphere 1,4-benzoquinone/hydroquinone (Q/H2Q) redox reaction were chosen to test the electrochem. properties of the electrodes. The properties of the diamond electrodes were found to undergo strong modification as a function of surface treatment. The active surface area and the reaction rate consts. decreased significantly upon anodic polarization. Important drops in the charge carrier concn. on the surface and in true surface area led to hindrance of electron transfer at the electrode. [on SciFinder (R)]