Electrochemically Modified Glassy Carbon for Capacitor Electrodes Characterization of Thick Anodic Layers by Cyclic Voltammetry, Differential Electrochemical Mass Spectrometry, Spectroscopic Ellipsometry, X-Ray Photoelectron Spectroscopy, FTIR, and AFM

Abstract

Glassy carbon (GC) is a well known material frequently used in analytical electrochemistry. Numerous investigations of the catalytic surface properties of activated GC have been reported. 1 The GC electrodes can be activated along different routes such as wet chemical, dry chemical, or electrochemical oxidation. Laser activation has also been suggested by Pontikos and McCreery. 2 The numerous possibilities for carbon surface activation have been described in articles and book by McCreery 3 and by Kinoshita. 4 In electrochemical activation, a number of choices exist as to how to modify the surface, such as galvanostatic, potentiostatic, or cyclic polarization in various electrolytes. Film growth by cycling and the corresponding optical properties of the active layer were investigated earlier in our laboratory using spectroscopic ellipsometry. 5 Electrochemical double-layer capacitors (EDLC), also called supercaps or ultracaps, utilize high-surface area electrodes in order to achieve a high-double-layer capacitance. Three main categories of electrode materials typically are used in these EDLCs, viz., carbons, polymers, and metal oxides. 6 For noble metal oxides such as RuO 2 specific capacitance of more than 700 F/g was reported, 7 but these materials are generally considered as being too costly. Redox active polymer films are also considered to be potential electrode materials for EDLCs, 8 but most of them are rather slow, and their long-term stability and cycle life are still uncertain. High-surface area carbons are relatively inexpensive EDLC electrode materials with a relatively high specific capacitance of up to 100 F/g. 9 Therefore, in most of the capacitors available today, carbon materials are used for the electrodes. Problems still arise from the contact resistance between carbon powder particles and from that between the active layer and the current collector sheet. Metal particles or fibers have been added to the carbon powder in order to overcome the grain-to-grain resistance. 10 The use of GC for electrochemical EDLCs was suggested about 20 years ago in a patent by Miklos et al. 11 Activation of the GC surface was attained by gas-phase oxidation at elevated temperatures. Electrochemical activation was not considered in that patent.Several advantages are expected from modified glassy carbon when this is used as an electrode material in EDLCs. It is a reasonably good electronic conductor (200 S/cm) 1,12 and can therefore also be used as the current collector. In addition, GC is impermeable to gases and ions, so that a bipolar plate/electrode assembly (BPEA) can be created by simply modifying a glassy carbon sheet on both sides. 13 However, when working with GC one has to be aware of the fact that depending on the precursor material and temperature used during the pyrolysis process, rather different kinds of GC exist. 1 Properties such as the conductivity, density, reactivity, number, and diameter of internal closed pores, etc. are determined by the pyrolysis temperature. GC is still considered an expen...

Chemical and electrochemical characterization of porous carbon materials

“…Thus, their use in 28 catalysis (either as catalyst or support), adsorption in solu-29 tion or electrochemical processes are three examples in 30 which the surface chemistry can have an important rele-31 vance in the materials performance [1][2][3][4][5]. Specially, any 32 discussion on the electrochemical behaviour of carbon, 33 such as its performance as double layer capacitor, which 34 is being very much studied nowadays, should take into 35 account the carbon electrode/electrolyte interface, where 36 functional groups play an important role, mainly in aque-37 ous medium [1,[3][4][5][6][7][8][9][10][11][12][13][14][15][16]. 38 The presence of surface heteroatoms, especially oxygen 39 groups, affects the electrochemical response of the carbon 40 materials in two different ways.…”

Enhanced Adhesion of Ultrathin Nanoporous Au Deposits by Electrochemical Oxidation of Glassy Carbon

“…29,35 Different oxidation times were employed in order to assess potential correlation between the oxidized layer thickness and the strength of adhesion of the metal deposit on accordingly treated GC substrates. Figure 2A shows chronoamperometry results from the deposition of Au 0.3 Ag 0.7 alloy after EO treatment of the GC.…”

“…There is good precedent demonstrating an increase in background charging currents on glassy carbon following EO treatments affirming this result. 21,29,30,35 This effect on NPG can be primarily attributed to the lack of continuity of the alloy and NPG following deposition as illustrated by Figure 3B. This implies that the EO makes the Pb UPD based surface area measurements somewhat ambiguous, rendering the technique less effective for measuring SA and monitoring its dynamics upon de-alloying or adhesion testing.…”

“…Thus, in the absence of pore opening the surface looks more like untreated GC than TO. However, taking into account the largely accepted in the literature [27][28][29]35 assumption for termination of EO treated GC with oxygen-containing surface functional groups one would speculate that the dark layer or at least its top portion confines the O-species functionalization. Should this be the case, it is the darker layer that facilitates the decrease in the contact angle and enhance the hydrophilicity.…”

Automatic Determination of Uric Acid in Urine in a FIA System with a Tubular Amperometric Detector

“…This dilution requires an elevated degree of sensitivity in the measurement process, to detect reduced concentrations of UA, in the presence of other compounds. In the proposed method, the working electrode was activated electrochemically with the objective of increasing the sensitivity of the amperometric determination [10], permitting the surface of the electrode to be increased by promoting the opening of the pores of the glassy carbon structure [17].…”