Does the capture threshold coincide with the pme?
At which potential does the interfacial water reverse its preferred orientation, and how does this potential depend on surface structure, electrolyte and cation?
Laser-induced current transients (LICT) perturb the interface by a temperature jump; the sign of the transient changes at the pme. EFCE perturbs the interface electrically: an external field holds the faradaic current at a setpoint during the potential sweep.
Since the differential susceptibility of the interfacial water is largest at vanishing net orientation, we expect the capture threshold close to the pme. If this holds, the pme could be determined at a 5 µm microdisc without a laser.
Capture threshold and pme at comparable Pt surfaces
- LICT at Pt in 0.05 M H₂SO₄ in the established set-up: determination of the pme.
- EFCE at a 5 µm Pt microdisc with the same electrolyte and the same pretreatment: determination of the capture threshold at low scan rate.
- Optional: LICT with and without an applied additional field: shift of the pme.
EFCE provides an electrical, spatially confined pme determination at microelectrodes.
Field sensitivity and entropy maximum are different interfacial parameters; the deviation itself is the measured quantity.
- Whether the external field reaches the interface has not been demonstrated (Debye length ≈ 1.2 nm).
- The capture threshold was observed in 1999 and has not yet been re-measured with the generation 2 cell.
- In two-electrode operation the reference electrode carries the measuring current; its behaviour under load is being characterised.
- LICT at a 5 µm disc is practically not feasible; the comparison therefore requires comparable surfaces rather than the same electrode.