At which potential can the current be captured?

1. The faradaic current at a Pt microdisc electrode (Ø 5 µm, 0.05 M H₂SO₄) is held at a setpoint by an external electric field while the electrode potential is varied.
2. The measured quantity is the controller output, i.e. the field strength required to keep the current constant, as a function of potential (control curve).
3. The capture threshold is the potential from which the control first holds the setpoint current. The control curve follows from there.

The response of a dipole layer to an additional field is determined by its differential susceptibility. It is largest when the mean orientation of the water molecules at the interface is zero, and decreases with increasing pre-polarisation. We therefore expect the capture threshold to lie close to the potential at which the interfacial water reverses its preferred orientation.

If this holds, the capture threshold would be an electrically accessible, local indicator of the potential of maximum entropy (pme) at microelectrodes.

Five research areas

Debye length

≈ 1.2 nm in 0.05 M H₂SO₄. Whether the external field reaches the interface is unresolved; three control experiments are planned.

Reference

In two-electrode operation the reference electrode carries the measuring current. Its behaviour under load is characterised separately.

Field values

Stated field strengths refer to the space between field electrode and working electrode, not to the interface.

Use

The method has been published (Electroanalysis, 1999) and is therefore open for unrestricted use.