Digital potentiostat

Goldsworthy, William W.; Clem, Ray G.

doi:10.1021/ac60306a025

Cited by 17 publications

(8 citation statements)

References 2 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…With the interrupter method [36][37][38][39][40][41][42][43][44][45][46][47][48] the polarization current is interrupted periodically for short times within the microsecond range. In these interrupter periods t 0 the ohmic voltage drop iR u disappears immediately, while the "true" polarization voltage E p of the working electrode only decreases slowly due to the storage capacity of the double layer C dl .…”

Section: Current Interrupt Methodsmentioning

confidence: 99%

The iR drop - well-known but often underestimated in electrochemical polarization measurements and corrosion testing

Oelßner¹,

Berthold

Guth

2006

Materials and Corrosion

107

View full text Add to dashboard Cite

At first sight the problem of the iR drop and its compensation in electrochemical polarization measurements seems to have only minor significance, but it has actually troubled electrochemists and corrosion scientists for more than a hundred years. For reducing the iR drop in the electrochemical cell, its computation, experimental determination and numerical or automatic electronic compensation numerous scientific and experimental work has been carried out and appropriate suggestions were submitted. These efforts led to commercially available potentiostats with sophisticated facilities for automatic iR compensation. Nevertheless, to date these possibilities have been utilized with a certain hesitancy. Many users underestimate the iR drop, regarding it often merely as a marginal problem, which only has to be taken into account in experiments with very high currents or extremely low conductivity of the electrolyte. Furthermore, there are also doubts and prejudices regarding modern methods of iR compensation, resulting from previous unpleasant experiences or reports on failed experiments with inappropriate equipment or imperfect methods. Reduction or automatic compensation of the iR drop is necessary more frequently than generally assumed and also in most cases possible. On the other hand the application of the different methods is still not completely uncomplicated and requires special experimental experience and care. The aim of the present work is it therefore to give a comprehensive retrospective overview of the ohmic drop problem and the relevant activities to overcome it.

show abstract

Section: Current Interrupt Methodsmentioning

confidence: 99%

The iR drop - well-known but often underestimated in electrochemical polarization measurements and corrosion testing

Oelßner¹,

Berthold

Guth

2006

Materials and Corrosion

107

View full text Add to dashboard Cite

show abstract

“…The pulsed ramp and differential amplifier were those normally used in the differential pulse polarography mode of the 174 Polarographic Analyzer. To minimize instrumental artifacts of the kind recently reported (7), time constants in the sample-and-hold circuitry were decreased by a factor of 100 compared with those supplied by the manufacturer. All measurements were made with a three-electrode system with Ag/AgCl as the reference electrode and platinum as the auxiliary electrode.…”

Section: Methodsmentioning

confidence: 99%

Application of direct digital control of electrode potential to controlled-potential electrolysis experiments

Pomernacki¹,

Harrar²

1975

Anal. Chem.

View full text Add to dashboard Cite

A mlnlcomputer program and electronlc hardware have been developed for controlllng the potentlal of an electrode through the medlum of an algorlthm wlthln the computer. The control algorlthm found to be satlsfactory Is the dlscrete equlvalent of proportlonal-plus-Integral actlon. Control func= tlone are carrled out In assembly language at a sampllng rate of 1 kHz; the parameters that govern the control actlon and electrolysls condltlons can easlly be changed on-llne vla a hlgh-level conversatlonal language. Theory has been developed for guidance In tunlng the controller for varlous electrolysls cell characterlstlcs. Detalled control obJectlves and speclflcatlons have been formulated for typical electrolysls experlments. The system has been tested wlth mercury-pool and platlnum worklng-electrode cells, demonstratlng that the control objectives can be met and that the theory Is useful. System rlsetlmes of lese than 8 msec can be achleved, and steady-state control errors are not slgnlflcant. A malor fractlon of the tlme durlng each sampllng perlod ls available for other data processlng.The direct digital control (DDC) of the potential of the working electrode in a 3-electrode cell has been viewed as an interesting possibility (1, 2 ) ever since the advent of minicomputers. In contrast to computer-controlled potentiostats (see, for example, Refs. 1-61, where the feedback control is still accomplished by means of an analog potentiostat, DDC of the electrode potential is a concept in which the control action is generated by means of a computational algorithm within the computer. This approach is also different from the type of digital control described by Goldsworthy and Clem (7, 8) and White (9), in which the control is effected through measurement of the electrode potential by means of a differential comparator, followed by a digital output. In their technique, which does not involve the use of a computer, the control action and its characteristics are fixed in hardware.Direct digital control via software has been widely implemented in industrial process control (10-121, but for a number of reasons has not yet found application in electrochemistry. One reason has been that a speed of response comparable to that of analog circuitry could not be attained because of computational speed limitations in the computer. Now, however, the existence of faster minicomputers, digital multiply/divide circuits, and advanced software techniques have enabled significantly faster data processing. At the present time, DDC would appear to be practical at least for laboratory-scale controlled-potential electrolysis, and possibly analytical voltammetry, because these techniques do not require very high control speeds.A second factor hindering the development of DDC in the laboratory has been the much greater cost of the digiAuthor to whom correspondence should be addressed.tal, compared to the analog approach. However, when the ubiquity and versatility of the minicomputer is considered, the use of DDC can be regarded much more favorably. ...

show abstract

“…The method of potentiostatic control used in the instrument is similar in principle to that used in the "digital potentiostat" of Goldsworthy and Clem (7). However, this device generates approximately 50-fold greater average current, and the charge injection circuitry is fundamentally more precise because capacitive discharge is employed here, rather than timed current injection.…”

Section: Description Of the Coulometermentioning

confidence: 99%

Coulostatic coulometer with digital counter

Last¹

1982

Anal. Chem.

View full text Add to dashboard Cite

A coulometer which is based on the coulostatic prlnclple has been developed and shown to be useful For analyses in low electrolyte (0.1 PA KNOB) solution. The instrument injects dlscrete charge pulses rind measures the cell potentlal between pulses when the current flowing through the bulk solution is negllglble. Thus, the cell potentlal can be measured precisely, free from any effects of the ohmic potential drop. As a result, the caulomettric performance of the Instrument is unaffected by the relatlve positioning of the reference and worklng electrodes. Lead determlnations were performed in 0.5 M or 0.1 M KNO, scalutlon, and the reference electrode was positioned off the axis of minimum separatlon between the working and auxlllary electrodes, in order to test the instrument's performance under adverse conditions. The preclslon and accuracy ranged from 0.09 % to 0.05 % (relative error) for lead samples Iin the range 1-8.5 mg, respecllvely (3.5 mL cell volume).Coulometry is a technique characterized by high current, and therefore a large ohmic potential drop exists in the solution during the analysis. The ohmic potential drop can, and generally does, lead to a nonuniform potential distribution across the surface of the working electrode. In unfavorable cases, the potentials measured at various locations on the surface of the working electrode may differ by more than 100 mV (1). A potential variation of this magnitude could easily lead to an erroneous coulometric result due to competing side reactions. One consequence of this problem is that cell ge. ometry (i.e., the relative orientation of the three electrodes) can critically affect the performance of the coulometer (2). The best behavior is usually obtained for cells whose working and auxiliary electrodes are axially symmetric and separated by a distance roughly equal to the radius of the working electrode. The reference electrode should be placed on the line of minimum separation between the other electrodes. situated as close as possible to the working electrode.The coulostatic electrochemical technique is essentially immune (3-6) from the effects of the ohmic drop which exists in the solution. The immunity derives from the fact that the potential is measured at times when no current flows in the bulk solution. This is accomplished by applying the current in the form of discrete charge pulses which are applied intermittently to the cell. Within the time period between pulse applications, it is possible to measure the potential across the electrical double layer without any error due to ohmic contributions. A coulometer, which is based on the coulostatic principle, has been developed and shown to be useful in eliminating many of the problems associated with the ohmic potential drop. DESCRIPTION OF T H E COULOMETERA block diagram of the instrument is shown in Figure 1. A precision pulse generator can apply a precise increment of charge (via the auxiliary electrode (A)) to the electrical double layer which exists a t the interface between the working electrode (W...

show abstract

Digital potentiostat

Abstract: A Digital PotentiostatSir: Reported, for the first time, is an instrument for potentiostatic control of an electrochemical cell employing a new technique-digital current feedback. Digital current pulses, which can be scaled to read-out directly on a scaler the

Cited by 17 publications

References 2 publications

The iR drop - well-known but often underestimated in electrochemical polarization measurements and corrosion testing

The iR drop - well-known but often underestimated in electrochemical polarization measurements and corrosion testing

Application of direct digital control of electrode potential to controlled-potential electrolysis experiments

Coulostatic coulometer with digital counter

Contact Info

Product

Resources

About