Structural characterization, electrochemical reactivity, and response stability of hydrogenated glassy carbon electrodes

The physical structure, electrochemical reactivity, and response stability of hydrogenated glassy carbon (HGC) electrodes were investigated using atomic force microscopy (AFM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), static secondary ion mass spectrometry(SIMS), cyclic voltammetry, and chronocoulometry. The electrochemical results indicate that glassy carbon surfaces, modified in a hydrogen microwave plasma, exhibit lower background voltammetric currents, comparable electrochemical activity, enhanced S/B ratios, and improved response stability for several aqueous-based redox analytes, compared with polished (i.e., oxygenated) glassy carbon (GC). Also, negligible adsorption of anthraquinone-2,6-disulfonate (2,6-AQDS) occurs on HGC, unlike polished GC, a surface on which AQDS strongly physisorbs at high coverages. The hydrogenated surface contains very Little surface oxygen (O/C less than or equal to 0.03) and is hydrophobic with a contact angle of >65 degrees. Static SIMS measurements reveal a significant fraction of the surface is composed of aliphatic hydrocarbon species (e.g. CH3, C3H3, C2H5, C3H5, etc.). Rapid electrode reaction kinetics are observed for Fe(CN)(6)(3-/4-) and Ru(NH3)(6)(2+/3+); while slightly slower kinetics are observed for dopamine, 4-methylcatechol, and especially Fe2+/3+. The voltammetric response for all of these analytes is extremely stable even after 3 months of exposure to the laboratory air, indicating the hydrogenated surface resists deactivation more so than polished GC. The effect of the supporting electrolyte (NaF, NaCl, NaBr, KF, KCl, and KBr) on the k degrees for Fe(CN)(6)(3-/4-) was also studied. Unlike the case for GC, for which there is a significant electrolyte effect, particularly in KCl, only a weak electrolyte effect was observed for HGC. The results demonstrate that hydrogenation is a suitable modification method to activate and stabilize GC.