Surface chemistry and electron transfer kinetics of hydrogen-modified glassy carbon electrodes

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 Is 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 Delta E-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.