Apparatus and method for measuring electrochemical impedance at high speed

• US 6,339,334 B1
• Filed: 02/22/2000
• Issued: 01/15/2002
• Est. Priority Date: 02/24/1999
• Status: Expired due to Term

• Current Assignee: Ulsan National Institute of Science and Technology
• Original Assignee: Pohang University of Science and Technology Foundation
• Inventors: Yoo, Jung-suk, Park, Su-moon
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): LUK, LAWRENCE W
• Application Number:
  US09/507,460
• Time in Patent Office: 693 Days
• Field of Search: 324/425, 324/426, 324/428, 324/430, 324/432
• US Class Current: 324/425
• CPC Class Codes: G01N 27/416 Systems G01N27/27 takes precedence

Abstract

An apparatus and method for measuring an electrochemical impedance at high speed. The method for measuring the electrochemical impedance of an electrolyte at high speed includes applying a direct current (DC) voltage having the reaction potential of the electrolyte to the electrolyte via a counter electrode and, after a delay, applying a signal voltage, including a DC voltage added to a differentiated or integrated Dirac-delta function voltage, to the electrolyte; computing a digital data value related only to the differentiated or integrated Dirac-delta function voltage, obtained by converting signal current flowing in a working electrode via the electrolyte into a voltage, integrating or differentiating the voltage, and Fourier transforming the result of the integration or differentiation; and obtaining changes in magnitude and phase as a function of frequency based on the Fourier transform, to compute the impedance. By investigating impedances computed at intervals upon the application of a reaction potential and upon the application of a step voltage plus the reaction potential to the electrolyte, the influence of mass transfer and electron transfer in the electrolyte on the impedance measurement can be understood.

Claims

1. A method for measuring electrochemical impedance of an electrolyte at high speed comprising:

(a) applying a direct current (DC) voltage having the reaction potential value of an electrolyte to the electrolyte via a counter electrode and, after a delay, applying a signal voltage, including the DC voltage plus a differentiated or integrated Dirac-delta function voltage, to the electrolyte;

(b) computing a digital data value related only to the differentiated or integrated Dirac-delta function tion voltage from among digital data, obtained by converting a signal current flowing in a working electrode via the electrolyte into a voltage, integrating or differentiating the voltage, and Fourier transforming the voltage after integrating or differentiating to produce a Fourier transformed value; and

(c) obtaining changes in magnitude and phase, as a function of frequency based on the Fourier transformed value and thereby determining the impedance.

2. The method of claim 1, wherein the digital data value related only to the differentiated or integrated Dirac-delta function voltage is the difference between a digital data value obtained after the reaction potential is applied to the electrolyte and a digital data value obtained after applying the signal voltage, including the DC voltage plus the differentiated or integrated Dirac-delta function voltage, to the electrolyte.

3. The method of claim 1, wherein the voltage is differentiated and then Fourier transformed in (b) when the signal voltage, in which the integrated Dirac-delta function voltage plus the DC voltage is applied to the counter electrode in (a), and the voltage is integrated and then Fourier transformed in (b) when the signal voltage including the differentiated Dirac-delta function voltage plus the DC voltage is applied to the counter electrode in (a).

4. The method of claim 1, wherein the integrated Dirac-delta function voltage is 5-25 mV.

5. A method for measuring an electrochemical impedance at high speed comprising:

(a) generating a direct current (DC) voltage having the reaction potential of an electrolyte, converting the DC voltage into a current, and applying the current to the electrolyte via a counter electrode;

(b) after a first delay, converting a signal voltage, generated by adding a differentiated or integrated Dirac-delta function voltage to the DC voltage, into a current and applying the current to the electrolyte via the counter electrode;

(c) sampling an analog voltage applied to a working electrode via the electrolyte and converting the analog voltage into digital data;

(d) computing a digital data value related only to the differentiated or integrated Dirac-delta function voltage from the digital data, integrating or differentiating the digital data, and Fourier transforming the digital data after integrating or differentiating to produce a Fourier transformed value; and

(e) obtaining changes in magnitude and phase as a function of frequency from the Fourier transformed value to compute the impedance.

6. The method of claim 5, wherein the digital data value related only to the differentiated or integrated Dirac-delta function voltage is the difference between a digital data value obtained after the reaction potential is applied to the electrolyte and a digital data value obtained after a a second delay.

7. The method of claim 5, wherein the digital data is differentiated and then Fourier transformed in (d) when the signal voltage, in which the integrated Dirac-delta function voltage is added to the DC voltage, is applied to the counter electrode in (a), and the digital data is integrated and then Fourier transformed in (d) when the signal voltage, in which the differentiated Dirac-delta function voltage is added to the DC voltage, is applied to the counter electrode in (a).

8. The method of claim 5, wherein the integrated Dirac-delta function voltage is 5-25 mV.

9. An apparatus for measuring an electrochemical impedance at high speed comprising:

a signal generator for generating and outputting a direct current (DC) voltage, which is a reaction potential of an electrolyte, and outputting a signal voltage obtained by adding a step voltage to the DC voltage after a delay, in response to a control signal;

a potentiostat receiving the DC voltage and the signal voltage from the signal generator, applying the received voltage to a counter electrode in the electrolyte, and controlling a voltage to be applied to a working electrode in the electrolyte using a reference electrode;

a current-to-voltage converter for converting current flowing through the working electrode into an analog voltage;

a sampling unit for sampling the analog voltage and converting the analog voltage into digital data; and

a central controller for controlling the signal generator, the potentiostat, the converter, and the sampling unit, storing the digital data obtained when the DC voltage is applied and when the signal voltage is applied, at intervals, computing and differentiating differences between stored digital data, and obtaining changes in magnitude and phase at each frequency based on Fourier transforming differentiated differences and computing an impedance.

10. An apparatus for measuring an electrochemical impedance at high speed comprising:

a signal generator for generating and outputting a direct current (DC) voltage, which is a reaction potential of an electrolyte, and outputting a signal voltage obtained by adding a step voltage to the DC voltage after a delay, in response to a control signal;

a galvanostat for converting the DC voltage and the signal voltage into a constant current and applying the constant current to a counter electrode in the electrolyte;

a sampling unit for sampling an analog voltage applied to a working electrode in the electrolyte, through the electrolyte, and converting the analog voltage into digital data; and

a central controller for controlling the signal generator, the galvanostat, and the sampling unit, storing the digital data obtained when the DC voltage is applied and when the signal voltage is applied, at intervals, computing and differentiating differences between stored digital data, and obtaining changes in magnitude and phase at each frequency based on Fourier transforming differentiated differences and computing an impedance.