Polymer films on electrodes. 10. Electrochemical behavior of solution species at Nafion-tetrathiafulvalenium bromide polymers

The electrochemical behavior of solution species at electrodes consisting of a conductive polymer layer, produced by incorporation of tetrathiafulvalenium ( T T P ) bromide into the cation-exchange polymer Nafion, on various substrates (Pt, Ta, SnO,, n-Si) is described. The voltammetric behavior of the solution species Fe(CN),'and Fey2(where Ye = ethylenediaminetetraacetate) at the Nafion-TTF' electrodes was consistent with models of electrodes partially covered with electronically conductive sites. Microscopic investigation of the electrode showed that the incorporated TTF+ forms electroactive domains and conductive nonelectroactive crystals from electrochemical cycling. The nonelectroactive crystals have the same stoichiometry as the one-dimensional organic conductor TTFBro,7. In the electrodeposition of copper onto the TTF' polymer electrode, most deposited on the TTFBT,,~, indicating that they were the major source of electronic conduction within the polymer. When the TTF' polymer was applied to the surface of an n-type Si electrode, the lifetime of the semiconductor electrode for the photooxidation of Fe(I1) species was improved. Polymer electrodes consist of thin (-0.1-10 pm) polymer layers on conductive (metal or carbon) substrates.'-3 These include polymers containing electroactive groups in the polymer backbone and polyelectrolyte layers in which electroactive ions are held by electrostatic binding., In these materials charge is transported by diffusion and migration of the ions as well as by electron hopping between electroactive sites. Electronically conductive polymers3 and the related one-dimensional organic metals4 (e.g., (1) (a) Merz, A.; Bard, A. J. J . Am. Chem. SOC. 1978, 100, 3222. (b) Itaya, K.; Bard, A. J. Anal. Chem. 1978, 50, 1487. (c) Van De Mark, M. R.; Miller, L. L. J . Am. Chem. Soc. 1978, 100,639. (d) Daum, P.; Murray, R. W. J . Electrochem. SOC. 1979, 103, 289. (e) Kaufman, F. B.; Engler, E. M. J . Am. Chem. SOC. 1979, 101, 547. (2) (a) Oyama, N.; Anson, F. C. J . Electrochem. Soc. 1980,127, 247. (b) Ibid. 1980,112, 271. (c) Rubinstein, I.; Bard, A. J. J . Am. Chem. SOC. 1980, 102, 6641. (d) Ibid. 1981, 103, 5007. (e) Oyama, N.; Anson, F. C. Anal. Chem. 1980, 52, 1192. (3) (a) Diaz, A. F.; Kanazawa, K. K. J . Chem. SOC., Chem. Commun. 1979,635. (b) Kanazawa, K. K.; Diaz, A. F.; Geiss, R. H.; Gill, W. P.; Kwak, J. F.; Logan, J. A.; Rabolt, J. F.; Street, G. B. Ibid. 1979, 854. (c) Diaz, A. F.; Castillo, J. I. Ibid. 1980, 397. (d) Kanazawa, K. K.; Diaz, A. F.; Gill, W. D.; Grant, P. M.; Street, G. B.; Gardini, G. P. Synth. Met. 1979/1980, 1 , 329. (e) Bull, R. A,; Fan, F. R.; Bard, A. J. J . Electrochem. SOC. 1982, 129, 1009. 0002-7863/82/1504-5862$01.25/0 TTF-TCNQ, where TTF is tetrathiafulvalene and TCNQ is Elgs] -(CF,CF,I,(CFCF, Iy I O(C,F,)OCF,CF,SO,-Na+