**4.2.1 PPy-based anodes**

142 Electropolymerization

greatly improved by introducing organic or inorganic materials embedded within the polymer structure by electropolymerization. It is reported that the composites with micronand submicron ceramic particles such as TiO2 (Ferreira et al., 2001), WO3 (Yoneyama et al., 1990), Fe3O4 (Garcia et al., 2002), MnO2 (Yoneyama et al., 1991) and Zn3(PO4)2 (Lenz et al.,

Electrochemically polymer (PANI+PPy) coated stainless steel plates showed improved corrosion resistance with acceptable contact resistance under proton-exchange membrane fuel cell (PEMFC) condition (Joseph et al., 2005). Recently, it has been demonstrated (Ren & Zeng, 2008) that a bilayer conducting polymer coating, composed of an inner layer of PPy with large

corrosion of the type 304 stainless steel, used for bipolar plates of a PEMFC, much more effectively than the single PPy coatings in 0.3M HCl. Besides these, some PPy-based composites such as PPy-CMC (carboximethylcellulose), PPy-SDS (sodium dodecylsulfate), PPy-TiNT (Titanate nanotube) and PPy-zinc phosphate were observed to protect steel (Herrasti & Ocoan, 2001), 1Cr18Ni9Ti stainless steel (Zhang &Zeng, 2005), stainless steel type 904L (Herrasti et al., 2011), and AISI 1010 steel (Lenz et al., 2007) surfaces effectively from

PPy/PANI (Panah & Danaee, 2010) and Pt/PPy (Rahman, 2011) composite films provided noticeable corrosion inhibition for carbon steel, whereas PPy-TiO2 (Lenz et al., 2003), PPhe (polyphenol)/PPy (Tuken et al., 2004), PPy-P (Hosseini et al., 2007), PPy-DGEBA (Riaz et al.,

PPy-based coatings were also found to reduce the corrosion of oxidizable metals such as Fe (Bazzaoui et al., 2006; Bazzaoui et al., 2005; Lee et al., 2005), Al (Bazzaoui et al., 2005; Lehr & Saidman, 2006a; 2006b)and Al alloys(Lehr & Saidman, 2006a; 2006b). The efficiency of corrosion protection of PPy depends on the nature of the doping agents (Balaskas et al.,

Electrochemically deposited PPy films on Cu displayed good protection against Cu corrosion in a 3.5% NaCl solution (Herrasti et al., 2007). The effectiveness of the protection is enhanced when the PPy film is electrosynthesized from a solution of dihydrogen phosphate

PPy films electrodeposited onto Ni-Ti alloy employing sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol OT or AOT) solutions improved the corrosion performance of the alloy at the open circuit potential and at potentials where the bare substrate suffers pitting attack (Flamini & Saidman 2010). PPy coatings on Mg alloy AZ91D, obtained respectively from aqueous solutions of a dicarboxylic organic acid salt (Turhan et al., 2011a) and sodiumsalicylate (Turhan et al., 2011b) by cyclic voltammetry (CV) method, demonstrated

In a fuel cell, the fuel (hydrogen, natural gas, methanol, ethanol, etc.) is electrochemically oxidized at the anode, whereas the oxidant (oxygen from the air) is reduced at the cathode. Because of difficulties involved in the production, storage, and distribution of hydrogen, the use of alcohols (methanol, ethanol, etc.) as hydrogen carrier is preferred and the resulting cell is called as the direct alcohol fuel cell (DAFC). Thus, the overall efficiency of a DAFC depends upon the efficiencies of both the electrode reactions (e.g. alcohol oxidation and

3- (Kowalski et al., 2008), and PPy-PANAP (poly(5-amino-1-naphthol))

<sup>2</sup>− groups, reduced the

2- (Sabouri et al., 2009),

2007) with PPy improved the mechanical and corrosion resistance of the coatings.

dodecylsulfate ionic groups and an external PANI layer with small SO4

corrosion, respectively. Electrochemically prepared PPy-WO4

(Bereket & Hur, 2009) provided better protection for corrosion of mild steel.

(Redondo & Breslin, 2007) or sodium saccharinate (Bazzaoui et al., 2007).

2007), PPy-PMo12O4

good corrosion protections of the alloy.

2011).

**4.2 Fuel cell** 

Several PPy-based anodes for fuel cells have recently been prepared and investigated for their applications in DAFCs. Most of them are decribed briefly in following lines.

In the MOR, Pt nano-particles decorated PPy-MWCNTS composite electrodes showed higher catalytic stability than Pt/MWCNTs binary catalyst, due to the synergic interaction between PPy and the carrier (Qu et al, 2010). Zhao et al. (2008a) demonstrated that the Pt nano-particles deposited on PPy-C with naphthalene sulfonic acid as dopant exhibit better catalytic activity than those on plane carbon in fuel cells. They also reported (Zhao et al., 2009) that bimetallic Pt-Co nano- particles co-deposited on PPy-MWCNT composite via over-oxidation treatment had higher catalytic activity towards methanol oxidation. Further, the MOR was observed to improve on the Pt-Fe/PPy-C catalyst compared to commercial Pt/C catalyst (Zhao et al., 2008b).

Mohana Reddy et al. (2008) examined the suitability of the cobalt-polymer-MWCNT composite electrode for the ORR in DMFCs and DEFCs by using Pt-Ru/MWCNT and Pt-Sn/MWCNT, respectively, as anode electrocatalysts. The study indicated an improved power densities for hydrogen, methanol and ethanol based fuel cells compared to the previously non Pt based electro-catlysts. Hammache et al. (2001) observed a higher catalytic activity for MOR on the dispersed gold micro particle on PPy coatings on Fe than a bare gold electrode in acidic media.

The application of PPy film containing nanometer-sized Pt and Pt/Pd bimetallic particles on ITO glass plates has also been investigated as anode for MOR. The modified electrode was found to exhibit significant electrocatalytic activity. The enhanced electrocatalytic activities may be due to the uniform dispersion of nanoparticles in the PPy film and a synergistic effect of the highlydispersed metal particles so that the PPy film reduces electrode poisoning by adsorbed CO species (Selvaraj et al. 2006). A Pd/PPy/Pd/G generated by sequential electrodeposition method (Ding et al., 2011) showed a satisfactory electrocatalysis toward the formic acid oxidation.
