Powdered Active Carbon Electrodes PACE

VOLTAMMETRY OF POWDERED ACTIVE CARBON ELECTRODES (PACE) 

7 (a) Overall view of the electrochemical cell 1, PACE 2, SCE 3, Pt reference, (b) Cross-section of the powdered acuve carbon electrode 1, carbon powder 2, Pt contact. (From Refs. 27 and 194.) 

Thus the potential in the macropores is directly affected by transport and charging phenomena in the micropores accessible to electrolyte. These properties of active carbon render it a difficult material to use as an electrode. The large electrochemically active surface area leads to considerable double-layer charging currents, which tend to ob.scure faradic current features. The network of micropores in the electrode material might be expected to result in a significant ohmic effect, which would further impair the potential resolution (IR drop on electrode material) obtainable by PACE voltammetry. CV curves recorded with different masses (and sediment layer thicknesses) of powdered samples of selected carbons in various electrolyte solutions are presented in Fig. 8 as an example [194]. Where amounts of material were greater than 20 mg, the CVs recorded were of the same shape. 

It is expected that practical problems in using PACEs could arise as a result of electrical contacts between the sediment layer and the current collector, and with the mechanical durability of the electrode bed. The comparison of CVs for a Pt electrode and selected PACE (with the same current scale) is shown in Fig. 9 to illustrate the influence of Pt contact on the voltammograms recorded. Similar results were obtained using graphite, glassy carbon, or Au as contact materials 

The Influence of Carbon Surface Modification on the Shape of Cyclic Voltammograms in Aqueous Solution 

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Therefore the electrochemical response with porous electrodes prepared from powdered active carbons is much increased over that obtained when solid electrodes are used. Cyclic voltammetry used with PACE is a sensitive tool for investigating surface chemistry and solid-electrolyte solution interface phenomena. The large electrochemically active surface area enhances double layer charging currents, which tend to obscure faradic current features. For small sweep rates the CV results confirmed the presence of electroactive oxygen functional groups on the active carbon surface. With peak potentials linearly dependent on the pH of aqueous electrolyte solutions and the Nernst slope close to the theoretical value, it seems that equal numbers of electrons and protons are transferred. 

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