Electrochemical Performance of Diamond
Thin-Film Electrodes from Different Commercial
Sources
Anne E. Fischer
Yoshiyuki Show
Greg M. Swain
10.1021/ac035214o.s001
https://acs.figshare.com/articles/journal_contribution/Electrochemical_Performance_of_Diamond_Thin_Film_Electrodes_from_Different_Commercial_Sources/3340936
The electrochemical properties of two commercial (Condias, Sumitomo) boron-doped diamond thin-film electrodes were compared with those of two types of boron-doped diamond thin film deposited in our laboratory
(microcrystalline, nanocrystalline). Scanning electron microscopy and Raman spectroscopy were used to characterize the electrode morphology and microstructure,
respectively. Cyclic voltammetry was used to study the
electrochemical response, with five different redox systems serving as probes (Fe(CN)<sub>6</sub><sup>3-/4-</sup>, Ru(NH<sub>3</sub>)<sub>6</sub><sup>3+/2+</sup>,
IrCl<sub>6</sub><sup>2-/3-</sup>, 4-methylcatechol, Fe<sup>3+/2+</sup>). The response for
the different systems was quite reproducibile from electrode type to type and from film to film for electrodes of
the same type. For all five redox systems, the forward
reaction peak current varied linearly with the scan rate<sup>1/2</sup>
(ν), indicative of electrode reaction kinetics controlled by
mass transport (semi-infinite linear diffusion) of the
reactant. Apparent heterogeneous electron-transfer rate
constants, <i>k</i>°<sub>app</sub>, for all five redox systems were determined from Δ<i>E</i><sub>p</sub>−ν experimental data, according to the
method described by Nicholson (Nicholson, R. S. <i>Anal.
Chem</i>. <b>1965</b>, <i>37</i>, 1351.). The rate constants were also
verified through digital simulation (DigiSim 3.03) of the
voltammetric <i>i</i>−<i>E</i> curves at different scan rates. Good fits
between the experimental and simulated voltammograms
were found for scan rates up to 50 V/s. <i>k</i>°<sub>app</sub> values of
0.05−0.5 cm/s were observed for Fe(CN)<sub>6</sub><sup>3-/4-</sup>, Ru(NH<sub>3</sub>)<sub>6</sub><sup>3+/2+</sup>, and IrCl<sub>6</sub><sup>2-/3-</sup> without any extensive electrode pretreatment (e.g., polishing). Lower <i>k</i>°<sub>app</sub> values
of 10<sup>-4</sup>−10<sup>-6</sup> cm/s were found for 4-methylcatechol and
Fe<sup>3+/2+</sup>. The voltammetric responses for Fe(CN)<sub>6</sub><sup>3-/4-</sup> and
Ru(NH<sub>3</sub>)<sub>6</sub><sup>3+/2+</sup> were also examined at all four electrode
types at two different solution pH (1.90, 7.35). Since the
hydrogen-terminated diamond surfaces contain few, if
any, ionizable carbon−oxygen functionalities (e.g., carboxylic acid, p<i>K</i><sub>a</sub> ∼4.5), the Δ<i>E</i><sub>p</sub>, <i>i</i><sub>p</sub><sup>ox</sup>, and <i>i</i><sub>p</sub><sup>red</sup> values for
the two systems were, for the most part, unaffected by the
solution pH. This is in contrast to the typical behavior of
oxygenated, sp<sup>2</sup> carbon electrodes, such as glassy carbon.
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Ru
Scanning electron microscopy
app
Different Commercial Sources
redox systems
Fe
type
Δ E p
i p ox
film
electrode reaction kinetics
sp 2 carbon electrodes
response
scan rates