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Measuring principle

In voltammetry the potential is set and the current is measured. In EFCE the current is additionally controlled by an external field; the controller output is measured.

Measuring cell, generation 2

Fig. 2Schematic set-up, not to scale. The field electrode is located behind 6 µm of mica; the electrolyte gap between mica and microdisc is approx. 5 µm. The reference electrode is placed outside the cell in the inlet.

Working electrode: Pt microdisc, Ø 5 µm, embedded
Electrolyte: 0.05 M H₂SO₄
Field electrode: Pt wire, Ø 10 µm, behind 6 µm muscovite mica
Reference: Hg/Hg₂SO₄, chloride-free; two-electrode operation
Control: I controller, 100–1000 Hz, FPGA-based; manipulated variable field, controlled variable faradaic current

Procedure

Conditioning. Slow potential cycles largely remove the outer double layer; the inner Helmholtz layer is retained.
Potential sweep. The potential is varied slowly while the controller holds the faradaic current at the setpoint.
Capture threshold. Potential from which the control first takes effect at low field strength.
Control curve. Field strength as a function of potential above the capture threshold.

Finding

The control curve is independent of the setpoint current: anodic and cathodic setpoints as well as I = 0 yield the same curve. We therefore interpret it as a representation of the interfacial state rather than of the faradaic turnover.

First description: Schönweitz & Schönweitz, “Electric Field Coupled Electrode”, Electroanalysis 11 (1999) 957–963.