Gas diffiision electrode

T. Shimamune, Salt separation system using gas diffiision electrode, Soda Enso (Soda Chlorine), 1993, 44, 141 S. Holze, J. Jorissen, C. Fischer and H. Kalvelage, Hydrogen consuming anodes for energy saving in sodium sulphate electrolysis, Chem. Eng. Technol., 1994, 17, 382-389. 

In a hydrogen-oxygen fuel cell with liquid electrolyte, the reactants are gases. Under these conditions, porous gas-diffiision electrodes are used in the cells. These electrodes (Fig. 16.4) are in contact with a gas compartment on their backside and with the electrolyte on their front, facing the other electrode. 

Lizcano-Valbuena WH, Paganin VA, Gruizalez ER (2002) Methanol electro-oxidatirm on gas diffiision electrodes prepared with PtRu/C catalysts. Electrochim Acta 47 3715—3722... 

As is the case with fuel cells, depolarized cathodes have been considered for years but have not yet found wide commercial use in the chlor-alkali indusby. Reports of work in the 1970s and 1980s [117,118] described the use of solid-polymer electrolyte systems. Microporous electrodes are necessary for electrical continuity in these cells, and the cathode reaction takes place in the interior of the gas-diffiision electrode. Operating deficiencies include the gradual penetration of gas channels by caustic solution and the possibility of bulk flow of catholyte into the gas side of the electrodes. Section 17.2.2.2 describes more recent work that addresses these deficiencies. The first conunercial applications are beginning to appear. 

Although electrochemically prepared polypyrrole films are useful for fiindam tal studies, they are not practical for use in fuel cells. Apart firom the difficulty of their large scale production, their permeability is insufficient for generation of the large current densities (> 500 mA cm required of commercial cells. To circumvent these problems, we have used chemically prepared polypyrrole/poly(styr e-4-sulphate) powders, which we have raidered c tatalytic by the chemical deposition of Pt particles by various methods (7-9). These polypyrrole supported Pt catalysts can easily be mass-produced, and can be formed into catalyst layers for fuel cell gas diffiision electrodes using the technology currently used commercially for carbon supported catal> ts. 

Our studies of chemically prepared catalyst powders in gas diffiision electrodes have demonstrated that conducting polymer supported catalysts can provide similar current densities to commercial carbon supported catalysts. They indicate that with further optimization, the ion conducting properties of certain polymer support catalysts may allow them to exceed the performance of carbon supported catalysts. However, it is clear that substantial improvements in the stability of the polymer support materials will have to be made before applications in fuel cells can be realized. 

Ciureanu M, Wang H. Electrochemical impedance study of electrode-membrane assemblies in PEM fuel cells I. electro-oxidation of H2 and H2/CO mixtures on Pt-based gas-diffiision electrodes. J Electrochem Soc 1999 146 4031-40. 

Yang SC, Cutlip MB, StonehaitP (1990) Simulation and optimization of porous gas-diffiision electrodes used in hydrogen/oxygen phosphoric acid fuel cells. Electrochim Acta 35 869-878... 

Cabot, P.-L., Alcaide, F., and Brillas, E. (2009) Hydrogen reaction at open circuit in alkaline media on Pt in a gas-diffiision electrode. Journal of Electroanalytical Chemistry, 626,183-191. 

Yoon JW, GriUi ML, Bartolomeo ED, PoUni R, Traversa E (2001) The NO response of solid electrolyte sensors made using nano-sized LaFeOj electrodes. Sens Actuators B 76 483-488 Yoon SP, Nam SW, Kim SG, Hong SA, Hyun SH (2003) Characteristics of cathodic polarization at Pt/YSZ interface without the effect of electrode microstructure. J Power Sources 115 27-34 Yoon SP, Nam SW, Han J, Lim TH, Hong SA, Hyun SH (2004) Effect of electrode microstructure on gas-phase diffiision in solid oxide fuel cells. Solid State Ionics 166 1-11 Zhuiykov S (2007) Electrochemistry of zirconia gas sensors. CRC, Boca Raton, FL... 

In the discnssion of electrodes in SOFCs, the gas/solid interface played an important role. However, examining the possible elementary reactions shown in Figure 8.2 it is evident that reactions at solid/solid (electrode/SE) interfaces may take place. This is trae for electrode materials that allow diffusion of both electrons and ions (cases III and IV inFignre 8.2), and also for metals and semiconductors that allow only the diffiision of elections (or holes) if electrons have to cross the electrode/SE interface. A solid/solid interface arises also when insertion electrodes are applied on SEs and when a parent metal is used as an electrode on a compound, e.g., Ag on AgjS. 

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