To initiate and control the thermodynamically non-spontaneous interfacial electrosynthesis of PEDOT using a Ce 4+ oxidant (in the form of Ce(SO4)2), the aqueous|TFT interface must be polarised using a potentiostat in conjunction with a four-electrode electrochemical cell (see Supplementary Section S1 and Supplementary Fig. ). Herein, the external electrochemical driving force, the interfacial Galvani potential difference Δ o w 𝜙, was applied by CV using the electrochemical cell configuration described in Fig. . After 50 repetitive CV cycles (Fig. ), a homogeneous blue PEDOT thin film can be seen coating the polarisable L|L interface (Fig. ). The 50 CVs shown in Fig. poly(terthiophene), or poly(aniline). This increase in the charge accumulated is attributed to a combination of Faradaic and capacitive currents that arise due to the growth of the PEDOT thin film at the L|L interface, i.e., due to processes entirely separate from those that occur during electropolymerisation at a solid electrode|electrolyte interface. The structure of the electrical double layer (EDL) at a polarisable L|L interface differs from that at a solid electrode|electrolyte interface in that it consists of two back-to-back aqueous and organic EDLs. Thus, in the presence of a growing PEDOT thin film, capacitive currents in particular may arise from processes occurring simultaneously in the EDLs at the aqueous|PEDOT and PEDOT|organic interfaces, respectively. .