Surface Chemistry and Electron-Transfer Kinetics of Hydrogen-Modified Glassy Carbon Electrodes

Abstract

Gas-phase modification of glassy carbon (GC) was investigated in an attempt to make a C−H-terminated surface that is resistant to oxidation. By using a hot filament technique, hydrogen radicals were generated from a flow of hydrogen gas, and then the radicals attacked glassy carbon electrode surfaces. The modified glassy carbon surfaces were characterized first by X-ray photoelectron spectroscopy, where the shape of the carbon 1s band shows a distribution of carbon oxidation states different from a fresh polished surface. The oxygen-to-carbon atomic ratio is low (<3%) and stays low in air for weeks. Hydrogen treatment had minor effects on Ru(NH3)6 3+/2+ cyclic voltammetry but increased ΔE p for Fe3+/2+ from 176 to 466 mV for a scan rate of 0.2 V/s. There is no significant difference in voltammetry at fresh polished glassy carbon surfaces or hydrogen-modified surfaces for dopamine, Fe(CN)6 3-/4-, and ascorbic acid. Raman spectroscopy of modified surfaces shows a small decrease in carbon disorder compared to the fresh polished glassy carbon with both microscopic and macroscopic observations. All these observations are consistent with the etching of the GC followed by formation of a hydrogen-terminated carbon surface. We attribute the major decrease in electron-transfer rate for aquated Fe3+/2+ to the absence of catalytic carbonyl sites on the hydrogen modified carbon.

Electrochemically Assisted Covalent Modification of Carbon Electrodes

“…Most work to date has utilized acetonitrile as the modi®cation medium [2, 9±12, 18, 23, 26±38] but recent reports demonstrate that aqueous acid (H 2 SO 4 or HCl, pH < 2) may also be used [13,27]. Reduction of the diazonium can be effected by CV or controlled potential electrolysis, and successful modi®cation has been carried out at GC [2, 9±12, 18, 23, 26, 28±34], carbon ®ber and powder [2,18,27] edge plane and basal plane HOPG [2, 26, 30± 32, 35, 38], screen-printed graphite electrodes [13], hydrogenated GC (HGC) [36] and boron-doped diamond [37]. The wide range of aryl derivatives which have been grafted to carbon surfaces by diazonium reduction is listed in Table 2.…”

“…McCreery's group has reported the modi®cation of Hterminated GC via reduction of 4-nitrobenzene diazonium in anhydrous conditions [36]. HGC is produced by exposing GC to a hydrogen plasma, generating a surface with a low O : C ratio and, presumably, surface C±H bonds.…”

Characterization of a 2‐Benzo[c]cinnoline Modified Glassy Carbon Electrode by Raman Spectroscopy, Electrochemical Impedance Spectroscopy, and Ellipsometry

“…Surface by Cyclic Voltammetry Dopamine (DA) is a unique molecule used for the characterization of the modified surfaces [4,31,32]. It exhibits fast electron transfer kinetics at the bare GC electrode surface, but the electron transfer is completely blocked on the derivatized surfaces [32].…”

“…It exhibits fast electron transfer kinetics at the bare GC electrode surface, but the electron transfer is completely blocked on the derivatized surfaces [32]. It needs to be adsorbed on the surface to be oxidized.…”

Controlled Zn‐Mediated Grafting of Thin Layers of Bipodal Diazonium Salt on Gold and Carbon Substrates

“…The G Raman band appears at 1575 cm À1 and is related with the CÀC bond [42] produced by mechanical treatments including polishing [43] or chemical reactions due to changes on the hybridization of carbon from sp 2 to sp 3 . The intensity of the D band can range from close to zero in highly organized non-modified surfaces, to values comparable with those of the G band in damaged or modified substrates.…”