Polypyrrole oxygen reduction

Transition metal compounds, such as organic macrocycles, are known to be good electrocatalysts for oxygen reduction. Furthermore, they are inactive for alcohol oxidation. Different phthalocyanines and porphyrins of iron and cobalt were thus dispersed in an electron-conducting polymer (polyaniline, polypyrrole) acting as a conducting matrix, either in the form of a tetrasulfonated counter anion or linked to... 

Different electron-conducting polymers (polyaniline, polypyrrole, polythiophene) are considered as convenient substrates for the electrodeposition of highly dispersed metal electrocatalysts. The preparation and the characterization of electronconducting polymers modified by noble metal nanoparticles are first discussed. Then, their catalytic activities are presented for many important electrochemical reactions related to fuel cells oxygen reduction, hydrogen oxidation, oxidation of Cl molecules (formic acid, formaldehyde, methanol, carbon monoxide), and electrooxidation of alcohols and polyols. 

Similarly, octaethylporphyrin iron (lll)-(r-bonded pyrrole [(OEP)FePy], either adsorbed on a glassy carbon electrode, or buried in a polypyrrole film of different thickness (from 0.9 to 60 pm), deposited on a GC electrode, displays an excellent activity towards oxygen reduction leading to water production efficiencies of nearly 90% [150]. These [(OEP)FePy] electrodes buried into a PPy film are remarkably stable leading to a catalytic activity similar to that obtained with platinum electrodes and limited by the diffusion of dioxygen in the solution phase. 

C.S.C. Bose and K. Rajeshwar, Efficient electrocatalyst assemblies for proton and oxygen reduction the electrosynthesis and characterization of polypyrrole films containing nanodis-persed platinum particles, J Electroanal. Chem., 333, 235-256 (1992). 

J. Li and X. Lin, A composite of polypyrrole nanowire platinum modified electrode for oxygen reduction and methanol oxidation reactions, J. Electrochem. Soc., 154, B1074— B1079 (2007). 

Zhou et al. reported template-synthesized cobalt porphyrin/polypyrrole (TPPS-Co/PPy) nanocomposite and its electrocatalysis of oxygen reduction in a phosphate buffer solution (PBS) [97]. With the assistance of ultrasonication and different preparation procedures, the nanocomposite can be electrochemicaUy synthesized with uniform 2-D and 3-D nanostructures. Lines (a) and (b) of Figure 17.8 show the cyclic voltammograms of a cobalt... 

Figure 17.8 Cyclic voltammograms of (a) the TPPS-Co/PPy nanocomposite-coated electrode in the 02-saturated PBS (solid line) (b) the TPPS-Co/PPy nanocomposite-coated electrode in the N2-saturated PBS, and (c) the bare Au electrode in the 02-saturated PBS scan rate is 50 mV s (Reprinted with permission from Journal of Physical Chemistry C., Template-Synthesized Cobalt Porphyrin/Polypyrrole Nanocomposite and Its Electrocatalysis for Oxygen Reduction in Neutral Medium by Qin Zhou, Chang Ming Li, Jun Li et a ., 111, 30, 11216-11222. Copyright (2007) American Chemical Society)...

Ikeda, O., O. Okabayashi, N. Yoshida, and H. Tamura (1985). Spectroelectrochemi-cal study of oxygen reduction at metalloporphyrin-doped polypyrrole fibn electrodes. J. Electroanal. Chem. 191, 157-174. 

Elzing, A., A. Van Der Putten, W. Visscher, and E. Barendrecht (1987). The mechanism of oxygen reduction at iron tetrasuhonato-phthalocyanine incorporated in polypyrrole. J. Electroanal. Chem. 233, 113-123. 

Liu HS, Shi Z, Zhang JL, Zhang L, Zhang JJ (2009) Ultrasonic spray pyrolyzed iron-polypyrrole mesoporous spheres for fuel cell oxygen reduction electrocatalysts. J Mat Chem 19(4) 468-470... 

Yuasa M, Yamaguchi A, Itsuki H, Tanaka K, Yamamoto M, Oyaizu K (2005) Modifying carbon particles with polypyrrole for adsorptitm of cobalt ions as electrocatalytic site for oxygen reduction. Chem Mater 17 4278-4281... 

Oh HS, Oh JG, Roh B, Hwang I, Kim H (2011) Development of highly active and stable nonprecious oxygen reduction catalysts for PEM fuel cells using polypyrrole and chelating agenL Electrochem Commun 13 879-881... 

Cong HN, El Abbassi K, Gautier JL, Chattier P (2005) Oxygen reduction on oxide/ polypyrrole composite electrodes effect of doping anions. Electrochim Acta 50(6) 1369-1376... 

Shao Y, Cong HN (2007) Oxygen reduction on high-area carlxm cloth-supported oxide nanoparticles/polypyrrole composite electrodes. Solid State Itmics 178(23-24) 1385-1389... 

Zhang WM, Chtai J, Wagner P, Swiegers GF, Wallace GG (2008) Polypyrrole/Co-tetraphenylporphyiin modified carbon fibre paper as a fuel cell electrocatalyst of oxygen reduction. Electrochem Commun 10(4) 519-522... 

Olson TS, Pylypenko S, Atanassov P, Asazawa K, Yamada K, Tanaka H (2010) Anion-exchange membrane fuel cells dual-site mechanism of oxygen reduction reaction in alkaline media on cobalt-polypyrrole electrocatalysts. J Phys Chem C 114(11) 5049-5059... 

Another problem encountered in this work was that bofii the uncatalysed polypyrrole/PSS support and catalysed samples lost conductivity during storage. The conductivity of an uncatalysed polypyrrole/PSS sample decreased firom 3 S cm to 0.1 S cm over a period of 9 months under vacuum, while the conductivity of a Pt catalysed sample dropped firom 0.3 S cm to 10 S cm. Th e observations indicate that polypyrrole supported catalysts are unlikely to be suiteble for oxygen reduction in fuel ceils. 

The best oxygen reduction performance observed to date for a polyaniline supported catalyst is comparable to the best obtained with polypyrrole (Fig. 4) (8). As for polypyrrole, polyaniline supported catalysts lose conductivity during storage and are therefore unlikely to be suitable for use in fuel cells. 

Figure 14 also explains why polypyrrole and polyparaphenylene are not as environmentally stable as polythiophene. Undoped poly pyrrole is susceptible to oxidation by oxygen in air, since the potential for undoped polypyrrole is below the threshold for oxygen reduction. On the other hand, /7-doped polyparaphenylene has an oxidation potential greater than that for water and is unstable toward moisture. F-doped polyparaphenylene is reduced to a less doped, less conducting state. Although oxidized and neutral polyacetylene appear to be within the stability window, experimental results show that polyacetylene is not stable [293]. The chemical reactivity of oxygen toward the carbon-carbon double bonds or defect sites in polyacetylene may make polyacetylene unstable in air. 

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