Instrumentation galvanostat

Instrumentation Controlled-current coulometry normally is carried out using a galvanostat and an electrochemical cell consisting of a working electrode and a counterelectrode. The working electrode, which often is constructed from Pt, is also... 

The simplest of the methods employing controlled current density is electrolysis at constant current density, in which the E-t dependence is measured (the galvanostatic or chronopotentiometric method). The instrumentation for this method is much less involved than for controlled-potential methods. The basic experimental arrangement for galvanostatic measurements is shown in Fig. 5.15, where a recording voltmeter or oscilloscope replaces the potentiometer. The theory of the simplest applications of this method to electrode processes was described in Section 5.4.1 (see Eqs 5.4.16 and 5.4.17). 

The experimental setup included a three-electrode electrochemical cell with a liquid contact membrane electrode in which the internal Ag/AgCl electrode acted as a working electrode connected to a potentiostat/galvanostat. The instrument was capable of switching rapidly between potentiostatic and galvanostatic modes [51]. 

Electrochemical Equipment. Electrochemical experiments were performed using either a PAR Model 175 universal programmer and a PAR Model 363 potentiostat/galvanostat, or a Pine Instruments RDE-4 bipotentiostat, coupled with a Kipp and Zonen BD 91 X-y-y recorder. The current-time response for the chronoamperometry experiments was recorded with a Nicolet 4094 digital oscilloscope. All potentials were measured vs. a Ag/10"2 M Ag+ reference electrode. 

Figure 6.17. Schematic diagram of apparatus for galvanostatic measurements P, constant current power supply e, test electrode e2, reference electrode counter (auxiliary)-electrode V, potential-time recording instrument.

A galvanostatic perturbation, in principle, can be applied by means of a rather simple electrical circuit, as is represented in Fig. 3(a). (More sophisticated instrumentation, employing operational amplifiers, has been described in the literature see ref. 22). It is only required that the galvanostat resistance, Rg, be large compared with the equivalent cell resistance, so that the current forced through the cell is independent of the cell properties. If the source of electricity is a d.c. source, as in Fig. 3(a), a constant current I — jA will start to flow after the time t = 0 at which the circuit is closed [see Fig. 3(b)]. The effect of this action will... 

The instrumentation for coulometric titrations consists of a galvanostat (a constant-current source), a cell equipped with an endpoint detector, and a timer. 

Apparatus Cyclic voltammetry and amperometric current-time curves were obtained with a Pine Instrument Inc., Model RDE4 bipotentiostat and Kipp Zonen BD 91 XYY recorder equipped with a time base module. All measurements were performed in a conventional single-compartment cell with a saturated calomel electrode as the reference electrode and a Pt mesh as the auxiliary electrode at room temperature. Chronoamperometry was made with EG G Princeton Applied Research potentiostat/galvanostat Model 273 equipped with Model 270 Electrochemical Analysis Software. 

Potentiostats did not become commercially available until the late 1950s. Most earlier work was conducted either galvanostatically or potentiostatically, but with a two-electrode cell, in which one electrode served as both counter and reference electrode. Because of their complexity, potentiostats tend to have slower response times than galvanostats. It should be pointed out, though, that some of the limitations of potentiostats alluded to above are a matter of the past. With present day (1993) electronic components, it is possible to build home-made potentiostats, or to purchase commercial units, that make use of all the inherent advantages of potentiostatic measurements with little instrumental limitation, or none. 

The choice between galvanostatic and potentiostatic measurements depends on circumstances. From the instrumentation point of view, galvanostats are much simpler than potentiostats. This is not only a matter of cost, but also a matter of performance. Thus, where it is desired to measure very low currents (e.g., on single microelectrodes), a battery with a variable resistor may be all that is needed to set up a low-noise galvanostat. At the other extreme, when large currents must be passed — for instance, in an industrial pilot plant for electrosynthesis - power supplies delivering controllable currents in the range of hundreds of amperes are readily available, whereas potentiostats of comparable output are either nonexistent or extremely expensive. 

Operational amplifiers provide the fotmdation for electrochemical instrumentation. The aim of this chapter is to describe the main properties of an operational amplifier so as to imderstand the principles of potentiostats and galvanostats and to imderstand how they can be used for impedance measurements. 

The potentiostatic method is less ambiguous than the galvanostatic one. Its application, however, requires more sophisticated instrumentation. The rise time of the potentiostat should be fast enough to ensure rapid step change of the potential. Errors may arise from slow rise times as well as from current integration. With porous electrodes, all sites may not be under the same potential diffusion of reactant into or out of the pores may be slow compared with the potential change, which can lead to incorrect estimates of surface coverage and utilization. 

Figure 7.23 The portable PCS80 potentiostat-galvanostat (Reproduced by permission of Uniscan Instruments).

Figure 7.24 The wireless PalmSens potentiostat-galvanostat (right) and the pocket PC used to control it (left) (Reproduced by permission of Palm Instruments).

APPARATUS. An ECO (ECO instruments, Newton, MA) model 549 potentlostat/galvanostat was used for platlnization. All other... 

The quartz crystal nanobalance (QCN) can be combined with practically any electrochemical methods, such as cyclic voltammetry, chronoamperometry, chronocoulometry, potentiostatic, galvanostatic, rotating disc electrode [11], or potentiometric measurements. The EQCN can be further combined with other techniques, e.g., with UV-Vis spectroscopy [12], probe beam deflection (PBD) [13], radiotracer [14], atomic force microscopy (AEM) [15], and scanning electrochemical microscopy (SECM) [16]. The concept and the instrumentation of... 

R.D. Beach, R.W. Conlan, M.C. Godwin, et al, Towards a Miniature Implantable in Vivo Telemetry Monitoring System Dynamically Configurable as a Potentiostat or Galvanostat for Two- and Three-Electrode Biosensors, IEEE Transactions on Instrumentation and Measurement, vol. 54, no. 1, pp. 61-72, 2005. 

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