ABSTRACT
ABSTRACT The electrochemical behavior of diamond and graphitic carbon materials are summarized, with particular attention toward electron transfer reactivity. Carbon electrodes are considered with respect to three major variables that affect their electrochemical performance: electronic properties, surface cleanliness, and catalytic sites. The electronic properties vary significantly for ordered graphite, glassy carbon, and boron-doped diamond, and the density of electronic states can have a significant effect on electron transfer rates. In particular, ordered graphite exhibits outer sphere electron transfer rates that are two to four orders of magnitude lower that those on glassy carbon. Surface cleanliness is a strong function of surface preparation, particularly polishing, heat treatment, and anodization. For some outer sphere systems such as Ru(NH 3 ) 6 + / 2 + 3 https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203750469/7b216794-c74b-4b63-98ec-850a4e8d1fd1/content/in35_1.tif"/> , surface films have small effects on electron transfer rate because the electron can tunnel through thin films. For other systems, however, a surface catalytic site is necessary and adventitious surface films can dramatically decrease electron transfer rates. Surface oxides are an additional factor that affects reactivity, and methods to reduce or control surface oxide coverage are discussed. Oxide-free glassy carbon and closely related hydrogen terminated GC show quite different behavior toward those redox systems that are affected by surface functional groups. Finally, boron-doped diamond is discussed as a recent addition to the collection of carbon electrode materials with possible fundamental importance. Diamond represents an electrically conducting material with a very unreactive surface, and this property may be useful for analytical and electro-synthetic applications.
