Operational-Amplifier, Alternating-Current Polarograph with Admittance Recording.

Hayes, John W.; Reilley, Charles N.

doi:10.1021/ac60230a009

Cited by 27 publications

(15 citation statements)

References 5 publications

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“…Numerous schemes to reduce the sources of ohmic potential loss have been reported. Among the most recent and successful has been the application of the three-electrode potentiostat, a device which is frequently constructed from operational amplifiers (10,11,28,34,56,62,64,70,71). The threeelectrode potentiostat removes many of the sources of iR drop operative in normal voltammetric procedures.…”

mentioning

confidence: 99%

Some Investigations on Instrumental Compensation of Nonfaradaic Effects in Voltammetric Techniques.

Brown¹,

McCord²,

Smith³

et al. 1966

Anal. Chem.

109

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confidence: 99%

Some Investigations on Instrumental Compensation of Nonfaradaic Effects in Voltammetric Techniques.

Brown¹,

McCord²,

Smith³

et al. 1966

Anal. Chem.

109

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“…Several methods have been quoted in the literature, namely, arithmetical rectification of the I . R drop [30,311 and tailoring of measured data before outputting by impedance determinations [32][33][34][35][36]. Another procedure often employed in electroanalytical voltammetry makes use of internal electrochemical standards (37-391, i.e., a reversible electrochemical reaction is monitored in order to compare the real electrode peak potential m-ith the measured value E,,,,,,, given b!.…”

Section: Numerical Data Coirection After the Experiment If Rmentioning

confidence: 99%

Electronic configurations in potentiostats for the correction of ohmic losses

Souto

1994

Electroanalysis

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Recent trends in the design of potentiostats capable of correcting for ohmic losses occurring in electrochemical cells are reviewed. The various effects of ohmic drop occurrence and their influence on diverse electroanalJ.tica1 techniques are considered, as well as potentiostat configurations and stabilig., with emphasis in the three-electrode cell configuration. Electronic correction methods are discussed according to the following classifications: ( 1) positive feedback, ( 2 ) negative impedance, (3) current pulse, ( 4 ) analogic subtraction. and (5) current interruption. KEY WORDS: Potentiostat, Ohmic drop, Instrumentation SCOPE OF THE PROBLEMIn electrochemistry, controlled-potential experimem are performed b! . using a potentiostat. This instrument makes possible the automatic maintenance of the potential of the working electrode (WE) at a programmed value relative to the reference electrode (RE), irrespective of changes in the current passing through the electrolytic cell and/or in the solution resistance. In a three-electrode cell. such operation is continuously achieved by comparing the cell and reference signals, changing the potential of the counter electrode (CE) as necessary to compensate for any difference arising. That is, the cell current is increased or decreased to maintain the equaliK between rhe cell potential and the reference signal.Yet, the electrical characteristics of the electrochemical system have not been considered. From an electronic point of view, a three-electrode electrochemical cell can be regarded [ 11 as the network of impedances shown in Figure 1, where Z, and Zll. represent the interfacial impedances at CE and WE and the solution resistance is split into two portions, Rn and R,,, depending on the position of the reference electrode's probe in the current path. Ideally, the potentiostat should control the interfacial potential only, without interference of ohmic losses. However, the potentiostat is capable of compensating the ohmic drop in the solution except for its fraction occurring between RE and WE. That is, the controlled voltage contains a portion 1. R, of the total voltage drop in the solution. The presence of this uncompensated resistance loss keeps the potentiostat from giving an accurate control of the desired potential. Thus, a change of potential between these electrodes corresponds to a change of potential across the double layer of UC'E only if RE is not polarized and the 1 . R,, drop between them is negligible. But the potential-measuring probe in the electrol).te cannot measure at a point directly on the solution side of the double layer, thus causing a voltage drop that adds to the measured potential [l-31. The accurate control of potential is most important in cyclic voltammetn. The existence of the uncompensated resistance causes the potential sweep to be nonlinear: the distortion may be large enough so as to invalidate subsequent analysis in terms of a preconceived model ( e g , the expected dependence of current on the square root of scan rate for ...

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“…The positive feedback technique has long been employed by electrical engineers in amplifier design (10, I1), but has only recently been used in electrochemical studies. Several workers have given circuits devised to achieve compensation (i.e., reduce the effect of Re) in some cases (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23), but frequency limitations and phase instabilities have been the major causes of the lack of generality of these techniques. Further, there appears to be a rather major misconception about what the oscillations (whether damped or undamped) caused by too much positive feedback mean in terms of the degree of compensation.…”

Section: /Zf(s) + Casmentioning

confidence: 99%

“…To understand the significance of this, it is sufficient to examine how *min is defined in terms of both the cell and potentiostat parameters. Using [17] and [18] rmin may be defined as Tc--4Te (K + 1) 2 [21] which means that the time constant of the cell has to be considerably larger than that of the closed loop potentiostat in which case the minimum time constant contains only electrochemical parameters. Further examination of [20] indicates that, provided [21] is satisfied, it is possible for ru to become negative.…”

Section: August 1969mentioning

confidence: 99%

“…Using [17] and [18] rmin may be defined as Tc--4Te (K + 1) 2 [21] which means that the time constant of the cell has to be considerably larger than that of the closed loop potentiostat in which case the minimum time constant contains only electrochemical parameters. Further examination of [20] indicates that, provided [21] is satisfied, it is possible for ru to become negative. This, however, does not mean that overcompensation has taken place since the system still has a finite time constant, but merely means that Eq.…”

Section: August 1969mentioning

confidence: 99%

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High Speed Non-Faradaic Resistance Compensation in Potentiostatic Techniques

Pilla¹,

Roe²,

Herrmann³

1969

J. Electrochem. Soc.

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The general problem of the incorporation of IR compensation in a potentiostatic circuit is considered. The manner in which the number of time constants needed to describe the system affect the amount of stable positive feedback at short times or high frequencies is discussed and a theoretical model developed for present state of the art potentiostats and operational amplifiers. It is shown that the use of a model in which all series nonfaradaic resistance has been removed to establish a reference for complete IR compensation indicates that stable overcompensation cannot take place in any practical system. The use of positive feedback in pulse and a-c techniques is compared and it is concluded that great caution must be exercised in the latter with regard to the proper detection of optimum compensation. Interpretation of results using IR compensation is considered and it is shown that the use of frequency domain conversion to obtain the impedance of the system under, e.g., pulse conditions allows potentiostat parameters to be eliminated such that meaningful results may be obtained at times of the order of 10 nsec.

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Operational-Amplifier, Alternating-Current Polarograph with Admittance Recording.

Abstract: An alternating current polarograph, which permits automatic recording of the in-phase and quadrature components of the faradaic admittance, has been designed and constructed.

Cited by 27 publications

References 5 publications

Some Investigations on Instrumental Compensation of Nonfaradaic Effects in Voltammetric Techniques.

Some Investigations on Instrumental Compensation of Nonfaradaic Effects in Voltammetric Techniques.

Electronic configurations in potentiostats for the correction of ohmic losses

High Speed Non-Faradaic Resistance Compensation in Potentiostatic Techniques

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