where 𝜂 polarise is any additional overpotential required to polarise the L|L interface sufficiently positive of the PZC to enhance the interfacial concentration of Ce 4+ to the level required to initiate IET with appreciable kinetics, and 𝜂 EDL = 𝜂 PZC + 𝜂 polarise is the overpotential of the back-to-back EDLs at the L|L interface. To investigate the correlation between the potential-modulated variation of the interfacial concentration of Ce 4+ and Δ o w 𝜙 IET onset , the ionic distributions of Ce 4+ , H + , and SO4 in the aqueous EDL, and BA + and TB -in the organic EDL, were modelled as a function of the applied Δ o w 𝜙 at a polarisable aqueous|TFT interface (Fig. and Supplementary Figs. outlined in the electrochemical cell configuration described in Fig. , except for the EDOT monomers. The latter were excluded as the interfacial concentration of neutral EDOT is not expected to be influenced by the applied Δ o w 𝜙 during interfacial electrosynthesis. The model predicts that the interfacial concentration of Ce 4+ becomes significant when the applied Δ o w 𝜙 is 0.2 V more positive than the PZC (Fig. ). This predicted value correlates precisely with the experimentally determined value of 𝜂 polarise (= Δ o w 𝜙 IET onset -PZC) of 0.2 V. The latter was determined from the experimentally measured Δ o w 𝜙 IET onset of ca. 0.3 V (from the 3 rd cycle at 25 mV•s -1 in Fig. ). The experimentally determined PZC prior to interfacial electrosynthesis was ca. 0.1 V, see the differential capacitance measurement in Fig. As Ce 4+ is tetravalent, the interfacial concentration of Ce 4+ is predicted to increase rapidly when 𝜂 polarise increases by scanning positively. For example, when 𝜂 polarise is 0.4 V, the interfacial concentration of Ce 4+ is ca. 1 M, orders of magnitude higher than the 2 mM bulk concentration (Fig. ). The robustness of the model is supported by the excellent correlation between the voltammetric features of the modelled and experimental CVs and differential capacitance curves (Supplementary Fig. ). Importantly, Δ o w 𝜙 IET onset lies well within the limits of the available Galvani polarisable potential window (PPW), and thus the kinetics of IET between Ce 4+ and EDOT monomers at the bare L|L interface is directly under external electrochemical control.