Electrosynthesis of photoactive copolymer P3HT/PT₃ films at a polarised liquid|liquid interface

This work presents an optimised methodology for the electrosynthesis of poly(3-hexylthiophene) (P3HT), achieved upon the addition of 2,2’:5’5’’-terthiophene (T3), which formed P3HT/PT₃ copolymer films. The parameters that affect the interfacial polymerisation were studied using the interfacial polymerisation of poly(3,4-ethylenedyoxythiophene) (PEDOT) as a model study system. These polymerisations used Ce(IV) as oxidant in the aqueous phase and yield free-standing films with thickness in the nanometer scale.

The interfacial polymerisation of PEDOT was studied at the interface between two immiscible electrolyte solutions (ITIES) formed between three different options of aqueous anions (ClO4 – , NO3 – and SO4 2– ) and two different organic solvents, such as α,α,α-trifluorotoluene (TFT) and 1,2-dichloroethane (DCE). This study shows that the spontaneity of the polymerisation depends on an interplay of various factors, such as the interfacial electron transfer potential (∆o w𝜙ET ), the interfacial tension (𝛾), and the Galvani potential of the interface (∆o w𝜙) in relation to the potential of zero charge (PZC) and the ∆o w𝜙ET. The order of spontaneity of the polymerisation follows the Hofmeister series (ClO4 – > NO3 – > SO4 2– ). Non-spontaneous systems are suitable for electropolymerisation under electrochemical control using cyclic voltammetry.

The fabrication of P3HT/PT3 films was achieved by either galvanostatic or potentiostatic methods. The copolymer self-standing thin P3HT/PT3 films were extensively characterised, showing better electrochemical and structural properties than the equivalent P3HT/PT3 films obtained in a conventional 3-electrode system on a solid indium tin oxide (ITO) electrode

The neutral and photoactive state of the P3HT/PT3 films was obtained by chemical alkaline undoping directly at the ITIES. The photoactive P3HT/PT3 films were used for the study of interfacial photoinduced electron transfer. The photogenerated electrons catalysed the oxygen reduction reaction (ORR) at the aqueous phase, which is significantly enhanced by the presence of decamethylferrocene (Me10Fc) in the organic phase, which acts as a hole scavenger. This process is pH dependant over a broad pH range. The highest photocurrents are obtained at acid pH, higher photon flux and higher Me10Fc concentration.