Electrochemical Behavior of Electrodes Modified with π-Conjugated Polymers in 0.5 M H2SO4 (aq) and 1 M KOH (aq) Electrolytes

Plantinum electrodes modified with 10 kinds of π-conjugated polymers have been prepared. These polymers include poly(pyridine-2,5-diyl) PPy, poly(2,2′-bipyridine-5,5′-diyl) PBpy, poly(3-octylthiophene-2,5-diyl) P3OcTh, and poly(6-hexylpyridine-2,5-diyl) P6HexPy. Films of PPy and PBpy behave as good H+-transporting materials in 0.5 M H2SO4 (aq). Plots of log i vs. V for electrodes modified with the polymers give linear lines in a current density region of 10−5.5—10−2 A cm−2. The slope of the line, β = dV/d(log i), depends on the kind of the polymer. Hydrophilic PPy and PBpy give a β value of 3.2 × 10−2 V, while hydrophobic P3OcTh and P6HexPy with long alkyl chains give a larger β value of 4.5 × 10−2 V. Diffusion coefficients of H+ in films of PPy, PBpy, and poly(quinoline-2,6-diyl) P(2,6-Q) are estimated to be larger than 10−7 cm2 s−1 from limiting currents at room temperature. The i–V curve of a P(2,6-Q)-modified Pt electrode shows a strong pH-dependence reflecting a chemical change of the polymer with pH...