Counter electrode, electrochemical

K. (2009) Fabrication and enhanced performance of a dye-sensitized solar cell with a C10l-poly(3,4-ethylenedioxyfhiophene) /Ti02/FTO counter electrode. Electrochem. Solid-State Lett., 12, E13-F16. 

Figure Bl.28.8. Equivalent circuit for a tliree-electrode electrochemical cell. WE, CE and RE represent the working, counter and reference electrodes is the solution resistance, the uncompensated resistance, R the charge-transfer resistance, R the resistance of the reference electrode, the double-layer capacitance and the parasitic loss to tire ground.

Figure C2.8.3. A tliree-electrode electrochemical set-up used for the measurement of polarization curves. A potentiostat is used to control the potential between the working electrode and a standard reference electrode. The current is measured and adjusted between an inert counter-electrode (typically Pt) and the working electrode.

Potentiometric measurements are made using a potentiometer to determine the difference in potential between a working or, indicator, electrode and a counter electrode (see Figure 11.2). Since no significant current flows in potentiometry, the role of the counter electrode is reduced to that of supplying a reference potential thus, the counter electrode is usually called the reference electrode. In this section we introduce the conventions used in describing potentiometric electrochemical cells and the relationship between the measured potential and concentration. 

Product Recovery. Comparison of the electrochemical cell to a chemical reactor shows the electrochemical cell to have two general features that impact product recovery. CeU product is usuaUy Uquid, can be aqueous, and is likely to contain electrolyte. In addition, there is a second product from the counter electrode, even if this is only a gas. Electrolyte conservation and purity are usual requirements. Because product separation from the starting material may be difficult, use of reaction to completion is desirable ceUs would be mn batch or plug flow. The water balance over the whole flow sheet needs to be considered, especiaUy for divided ceUs where membranes transport a number of moles of water per Earaday. At the inception of a proposed electroorganic process, the product recovery and refining should be included in the evaluation to determine tme viabUity. Thus early ceU work needs to be carried out with the preferred electrolyte/solvent and conversion. The economic aspects of product recovery strategies have been discussed (89). Some process flow sheets are also available (61). 

Figure 3.6-1 The electrochemical window of 76-24 mol % [BMMIM][(CF3S02)2N]/Li [(Cp3S02)2N] binary melt at a) a platinum working electrode (solid line), and b) a glassy carbon working electrode (dashed line). Electrochemical window set at a threshold of 0.1 mA cm. The reference electrode was a silver wire immersed in 0.01 m AgBp4 in [EMIM][BF4] in a compartment separated by a Vicor frit, and the counter-electrode was a graphite rod.

Reference electrode (RE) and potentiostatic setpoint are fed to the inverting and noninverting input of an operational amplifier. The counter-electrode (CE) is connected to the output of the operational amplifier. I (EC) electrochemical current. 

Figure 4a. Electrochemical cells for microwave conductivity measurements. Cell above microwave conduit (1) electrochemical cell (plastic tube, placed on working electrode material), (2) counter-electrode, (3) reference electrode, (4) electrolyte, (5) space charge layer, (6) diffusion layer, (7) contact to working electrode, (8) waveguide.

When a current I flows in an electrochemical cell, such as the one shown in Fig. 4.1, between the catalyst, or working electrode (W) and the counter electrode (C), then the potential difference Uwc deviates from its open-circuit value U c. The electrochemical cell overpotential t Wcis then defined from ... 

Figure 7.5. (a) Solid electrolyte cell consisting of an YSZ disk with working (Pt), reference (Au, Ag) and counter electrodes (Au). (b) Schematic diagram of the electrochemical reactor.21 Reprinted with permission from The Electrochemical Society. 

Figure 7.8. (a) Dependence of (Ptr RfAg) on potential UWR for the system Pt(W)-Ag(R) exposed to H2-He mixtures (open-symbols, Ph2 varying between 0.53 and 0.024 kPa) and H2-02 mixtures (filled symbols, p02=12 kPa, Ph2 varying between 0.28 and 7.8 Pa) open-circuit operation, T=673 K, Au counter electrode, (b) Work function of working (W) and reference (R) electrode as a function of open-circuit potential UWR.21 Symbols and conditions as in figure 7.8a. Diamonds show the literature41 values of 0,w(pt) and o,R(Ag)- Reprinted with permission from The Electrochemical Society. 

The electrochemical cell consists of high surface area Pd/C or unsupported Pd-Ru cathodes interfaced to Nafion with a Pt-black/H2 counter electrode. The cell configuration, as well as the reactions taking place on the anode and the cathode are the following ... 

When a positive current I is applied between the catalyst-electrode and the Pt counter-electrode, then the catalyst potential Urhe changes to more positive values (Fig. 10.1) and the following electrochemical (net charge-transfer) reactions take place at the Pt catalyst-electrode surface ... 

Figure 10.6. Electrochemical cell (1) reference electrode, (2) molten catalyst, (3) porous Pyrex membrane, (4) counter electrode, (5) gas inlet Pyrex tube, (6) working electrode.12 Reproduced by permission of the Electrochemical Society.

This implies that Electrochemical Promotion or NEMCA is an electrochemically controlled metal-support interaction. It also implies that metal-support interactions on these supports can be viewed as a self-driven wireless NEMCA system, such as the one explored by Cavalca, Haller and Vayenas for the CH3OH oxidation system under catalyst-counter electrode short-circuit conditions where gaseous 02 replenishes O2 in the YSZ support at the vicinity of the counter electrode.24... 

Electrochemical promotion, or non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA) came as a rather unexpected discovery in 1980 when with my student Mike Stoukides at MIT we were trying to influence in situ the rate and selectivity of ethylene epoxidation by fixing the oxygen activity on a Ag catalyst film deposited on a ceramic O2 conductor via electrical potential application between the catalyst and a counter electrode. 

We have previously considered the mechanism of electrospray ionization in terms of the charging of droplets containing analyte and the formation of ions as the charge density on the surface of the droplet increases as desolvation progresses. The electrospray system can also be considered as an electrochemical cell in which, in positive-ion mode, an oxidation reaction occurs at the capillary tip and a reduction reaction at the counter electrode (the opposite occurs during the production of negative ions). This allows us to obtain electrospray spectra from some analytes which are not ionized in solution and would otherwise not be amenable to study. In general terms, the compounds that may be studied are therefore as follows ... 

SXS measurements. (A) Single-crystal disk electrode, (B) Pt counter electrode, (C) Ag/AgCl reference electrode, (D) Mylar window, (E) electrolyte solution, (F) inlet for electrolyte solution, (G) outlet for electrolyte solution, (H) cell body, (1) micrometer, (J) electrode holder, (K) outer chamber, (b) Cell configuration for electrochemical measurement, (c) Cell configuration for SXRD measurement. (From Kondo et al., 2002, with permission from Elsevier.)... 

Spectroelectrochemical Cell Figure 5.4 shows spectroelectrochemical cells used in electrochemical SFG measurements. An Ag/AgCl (saturated NaCl) and a Pt wire were used as a reference electrode and a counter electrode, respectively. The electrolyte solution was deaerated by bubbling high-purity Ar gas (99.999%) for at least 30 min prior to the electrochemical measurements. The electrode potential was controlled with a potentiostat. The electrode potential, current, and SFG signal were recorded by using a personal computer through an AD converter. 

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