Method and apparatus for compensation of double layer charging current in electrochemical cells

• US 5,180,968 A
• Filed: 03/01/1991
• Issued: 01/19/1993
• Est. Priority Date: 03/01/1991
• Status: Expired due to Fees

• Current Assignee: The Research Foundation for The State University of New York (State University of New York)
• Original Assignee: The Research Foundation for The State University of New York (State University of New York)
• Inventors: Adinolfe, Nancy, Bruckenstein, Stanley
• Primary Examiner(s): Harvey, Jack B.
• Assistant Examiner(s): Regan, Maura K.
• Application Number:
  US07/665,607
• Time in Patent Office: 690 Days
• Field of Search: 324/425, 324/439, 324/71.1, 204/153.1, 204/153.11, 204/400, 204/402
• US Class Current: 324/71.1
• CPC Class Codes: G01N 27/4163 checking the operation of, or calibrating, the measuring apparatus G01N27/3274, G01N27/4175 and G01N33/0006 take precedence

Abstract

A method and apparatus for compensating for charging current at a working electrode of an electrochemical cell. And a method for measuring faradaic current at the working electrode. Includes measuring the current at the working electrode while a time-varying potential difference is applied between the working electrode and a reference electrode. And while the applied potential difference is held constant for a short time and the working electrode current is again measured, where this current is the faradaic current. The faradaic current is then filtered from the total current to determine the charging current thereby compensating for double layer charging current in the cell.

Claims

1. In an electrochemical cell having a reference electrode and, a working electrode and also having a time-varying potential difference applied between said electrodes, a method of measuring faradaic current at said working electrode, comprising interrupting said time-varying potential difference and temporarily applying a constant potential difference across said electrodes and measuring a current at said working electrode while said constant potential difference is applied, wherein said measured current is the faradaic current at said working electrode.

2. In an electrochemical cell having a reference electrode and a working electrode, a method of measuring charging current at said working electrode, comprising:

measuring a first current at said working electrode while a time-varying potential difference is applied between said working electrode and said reference electrode;

measuring a second current at said working electrode while a constant (non-time varying) potential difference is applied between said working electrode and said reference electrode, wherein said second current is the faradaic current at said working electrode; and

measuring a difference between said first current and said second current, wherein said difference represents the charging current at said working electrode.

3. In an electrochemical cell having a counter electrode, a reference electrode, and a working electrode, a method of compensating for charging current at said working electrode, comprising:

a. applying a time-varying potential difference between said working electrode and said reference electrode;

b. measuring a first current at said working electrode while said time-varying potential difference is being applied, wherein said first current includes a faradaic current component and a charging current component;

c. storing a first signal proportional to said first current in a first memory means;

d. applying a constant, non-time-varying potential difference between said working electrode and said reference electrode;

e. measuring a second current at said working electrode while said constant, non-time-varying potential difference is being applied, wherein said second current is said faradaic current component at an instant when said constant, non-time-varying potential difference is applied;

f. determining a second signal proportional to said second current;

g. determining a difference signal between said first and second signals;

h. scaling said difference signal in magnitude and sign and summing said difference signal with said time-varying potential difference to produce a third signal, wherein said third signal is proportional to said charging current component; and

,

i. repeating steps a. through h. within preselected time intervals.

4. A method as recited in claim 3 wherein said first, second and third signals are voltages.

5. A method as recited in claim 3 wherein said time-varying potential difference is applied in repetitive cycles to said electrochemical cell and said non-time-varying potential difference is repetitively applied for a time period in the range of 1% to 25% of the time for each said cycle.

6. In an electrochemical cell having a reference electrode and a working electrode, an apparatus for measuring faradaic current at said working electrode, comprising:

means for applying a time-varying potential difference between said working electrode and said reference electrode; and

means for temporarily interrupting said application of said time-varying potential difference by temporarily applying a constant current across said working electrode and said reference electrode; and

,

means for measuring current at said working electrode while said constant potential difference is applied, where said measured current is the faradaic current at the working electrode.

7. In an electrochemical cell having a reference electrode and a working electrode, an apparatus for measuring charging current at said working electrode, comprising:

means for measuring a first current at said working electrode while a time-varying potential difference is applied between said working electrode and said reference electrode;

means for measuring a second current at said working electrode while a constant (non-time varying) potential difference is applied between said working electrode and said reference electrode, wherein said second current is the faradaic current at said working electrode; and

means for measuring a difference between said first current and said second current, wherein said difference represents the faradaic current at said working electrode.

8. In an electrochemical cell having a counter electrode, a reference electrode, and a working electrode, an apparatus for compensating for charging current at said working electrode, comprising:

a. means for applying a time-varying potential difference between said working electrode and said reference electrode;

b. means for measuring a first current at said working electrode while said time-varying potential difference is being applied, wherein said first current includes a faradaic current component and a charging current component;

c. means for storing a first signal proportional to said first current in a first memory means;

d. means for applying a constant, non-time-varying potential difference between said working electrode and said reference electrode;

e. means for measuring a second current at said working electrode while said constant, non-time-varying potential difference is being applied, wherein said second current is said faradaic current component at an instant when said constant, non-time-varying potential difference is applied;

f. means for determining a second signal proportional to said second current;

g. means for determining a difference signal between said first and second signals;

h. means for scaling said difference signal in magnitude and sign and summing said difference with said time-varying potential difference to produce a third signal, wherein said third signal is proportional to said charging current component; and

,

i. means for repeating steps a. through h. within preselected time intervals.

9. Apparatus as recited in claim 8 wherein said first, second and third signals are voltages.