Solid polymer electrolyte cells

The experimental setup is shown in Figure 9.23. The Pt-black catalyst film also served as the working electrode in a Nafion 117 solid polymer electrolyte cell. The Pt-covered side of the Nafion 117 membrane was exposed to the flowing H2-02 mixture and the other side was in contact with a 0.1 M KOH aqueous solution with an immersed Pt counterelectrode. The Pt catalyst-working electrode potential, Urhe (=Uwr)> was measured with respect to a reversible reference H2 electrode (RHE) via a Luggin capillary in contact with the Pt-free side of the Nafion membrane. 

Furan was dimethoxylated to give 2,5-dihydro-2,5-dimethoxyfuran, using electrogenerated bromine molecules generated from bromide salts in electrolyte solutions [71]. This reaction was characterized in classical electrochemical reactors such as pump cells, packed bipolar cells and solid polymer electrolyte cells. In the last type of reactor, no bromide salt or electrolyte was used rather, the furan was oxidized directly at the anode. H owever, high consumption of the order of 5-9 kWh kg (at 8-20 V cell voltage) was needed to reach a current efficiency of 75%. 

What can be learnt from XPS about electrochemical processes will be demonstrated and discussed in the main part of this chapter by means of specific examples. Thereby a survey of new XPS and UPS results on relevant electrode materials will be given. Those electrode materials, which have some potential for a technical application, are understood as practical and will be discussed with respect to the relevant electrochemical process. The choice of electrode materials discussed is of course limited. Emphasis will be put on those materials which are relevant for technical solid polymer electrolyte cells being developed in the author s laboratory. 

In the following chapter examples of XPS investigations of practical electrode materials will be presented. Most of these examples originate from research on advanced solid polymer electrolyte cells performed in the author s laboratory concerning the performance of Ru/Ir mixed oxide anode and cathode catalysts for 02 and H2 evolution. In addition the application of XPS investigations in other important fields of electrochemistry like metal underpotential deposition on Pt and oxide formation on noble metals will be discussed. 

For Cl2 or 02 evolution the stability of ruthenium based electrodes is not sufficient on a technical scale. Therefore the possibility of stabilizing the ruthenium oxide without losing too much of its outstanding catalytic performance was investigated by many groups. For the Cl2 process, mixed oxides with valve metals like Ti or Ta were found to exhibit enhanced stability (see Section 3.1), while in the case of the 02 evolution process in solid polymer electrolyte cells for H2 production a mixed Ru/Ir oxide proved to be the best candidate [68, 80]. 

The solid polymer electrolyte cells are viewed as being particularly appropriate for the treatment of high purity water systems, including the provision of ultra pure water for the pharmaceutical industry, cf. Ref. [205], The process is often coupled with UV radiation which serves to decompose unwanted, residual ozone [133],... 

Jones, R.C. LaConti, A.B. Nuttall, L.J. "Carbon Monoxide Monitor Features Hydrated Solid Polymer Electrolyte Cell", Proceedings, American Industrial Hygiene Conference, New Orleans, Louisiana, May, 1977... 

Fig. 13.17. Performance of advanced lightweight pressurized alkaline fuel cells. The dashed lines show initial advanced AFC cell results. A, 149 °C, 17 bar B, 140 °C, 17 bar C, 127 °C, 17 bar D, 110 °C, 4 bar E, 82°C, 4 bar F, 82 °C, 1 bar G, 0.2 MgPt-C and the same conditions as F (IR-free) H, 10 mg/cm2 Au/Pt, 127 °C, 1 bar (IR-free). , nominal performance of space shuttle cell (1000 h) , United Technologies target goal (1000 hr). Solid lines show solid polymer electrolyte cells for comparison under different pressure and temperature conditions. (Reprinted from Assessment of Research Needs for Advanced Fuel Cells, S. S. Penner, ed., Pergamon Press, 1986, pp. 14,87.)...

The development of solid polymer electrolyte cells is being actively conducted at General Electric Co. (13) and at Brown Boveri Research Center, Baden, Switzerland (14). As the name implies, the solid polymer electrolyte technology uses a solid polymer sheet as the sole electrolyte in the cells. It also acts as the cell separator. The majority of the present applications use Nafion with a thickness of 10-12 mils (13). Selected physical and chemical properties of Nafion 120 membranes are given in Table I. The membrane is equilibrated in water to approximately 30% water content prior to fabrication into a cell assembly. The hydrated membrane is highly conductive to hydrogen ions. It has excellent mechanical strength, and it is very stable in many corrosive cell environments. 

Reaction and transport at surface-catalyzed membranes used in solid polymer electrolytic cells and energy-conversion devices... 

Solid polymer electrolyte cell Electrol3dic passage of hydrogen ions across a solid pol3Tner membrane 95 99.8... 

Kordali, V., Kyriacou, G., Lambrou, C. (2000). Electrochemical synthesis of ammonia at atmospheric pressure and low temperature in a solid polymer electrolyte cell. Chemical Communications, 1673—1674. 

Fig. 5. Schematic of General Electric solid polymer electrolyte cell.

In solid polymer electrolyte cells (Fig. 5.7) the electrolyte is a thin perftuorinated sulphonic acid (Nafion) membrane (c, 0.2Smm thick) having a structure which promotes conduction of hydrated protons. The schematic cell reactions are shown in Fig. 5.7(a). Pure water is supplied to the anode where it is oxidized to oxygen and protons the latter pass through the polymer electrolyte to the cathode where hydrogen gas evolves. In fact, excess water is circulated through the anode compartment to remove waste heat. 

The solid polymer electrolyte cell tends to be slightly larger than corresponding high-pressure celK and requires a compressor to remove the hydrogen gas. However, it has a number of important advantages compared to other water... 

As shown in Fig. 5 7(b) the solid polymer electrolyte cell comprises a membrane, fuel cell type, porous electrodes and three further components z carbon collector, a platinized titanium anode support and a cathode support made from carbon-fibre paper The collector is moulded in graphite with a fluorocarbon polymer binder A 25 pm thick platinized titanium foil is moulded to the anode side to prevent oxidation. The purpose of the collector is to bnsure even fluid distribution over the active electrode area, to act as the main structural component of the cell, to provide sealing of fluid ports and the reactor and to carry current from one cell to the next E>emineralized water is carried across the cell via a number of channels moulded into the collector These channels terminate in recessed manifold areas each of which is fed from six drilled ports. The anode support is a porous conducting sheet of platinized titanium having a thickness of approximately 250 pm. The purpose of the support is to distribute current and fluid uniformly over the active electrode area. It also prevents masking of those parts of the electrode area which would be covered by the... 

Table 5A Typical pefforoaiaii of a solid polymer electrolyte cell...

Ffig. 5J Module voltage as a function of lime for a solid-polymer electrolyte cell stack (cf. Fig. 5.7)l Each module consists of 14 cathodes, each of area 0.093 m operating at 1.075 A cm and 55 C. 

Fig. 5 7 Solid-polymer electrolyte cells for water electrolysis, (a) Reactions, (b) The cell arrangement (c) A demonstration electrolyser module which incorporates 34 cells and will generate up to 14 m h of hydrogen. (Courtesy CJB Developments Ltd.)...

Some preliminary experiments were described in which the polymer design incorporates the structural elements required each for type of conductivity, and the mass transport parameters are evaluated with reference to the discharge rate of the polymer electrode in a solid polymer electrolyte cell. 

---