In the next step, nucleation and growth of adsorbed PEDOT oligomers takes place at the interface. The PEDOT oligomers act as floating interfacial bipolar electrodes, providing abundant catalytic sites as electrical short-cuts to catalyse IET between the Ce 4+ and EDOT species (Fig. (iii)). Due to this autocatalytic effect, IET proceeds at a much lower overpotential than at a bare ITIES, with a higher kinetic rate. Thus, the PEDOT islands show rapid 2D growth, parallel to the L|L interface. The gaps between individual rapidly growing islands of PEDOT disappear and a highly compact 2D PEDOT thin film coalesces at the ITIES that is flat on both sides, with a thickness of ~50 nm (Fig. (iv)). At this point, a physical barrier now exists between the Ce 4+ and EDOT species at the ITIES. However, IET continues through the conductive PEDOT thin film and is subject to the influence of the diffusion of SO4 2-counter-anions through the film to maintain electroneutrality locally, i.e., "p-doping". Continued IET initiates a secondary 3D growth process into the organic phase as the thickness of the PEDOT thin film increases. This controllable secondary growth process leads to the formation of a highly porous 3D structure, up to ~ 850 nm thick (Fig. ).