Polymer electrolyte membrane fuel cell electrodes

Outside of the double-layer region, water itself may be oxidized or reduced, leaving stable hydride, hydroxyl, or oxide layers on the electrode surface. These species may adsorb strongly and block sites from participating in electrocatalysis, as for example, hydroxyl species present at the polymer electrolyte membrane fuel cell... 

Kamarajugadda, S., and Mazumder, S. Numerical investigation of the effect of cathode catalyst layer structure and composition on polymer electrolyte membrane fuel cell performance. Journal of Power Sources 2008 183 629-642. Krishnan, L., Morris, E. A., and Eisman, G. A. Pt black polymer electrolyte-based membrane-based electrode revisited. Journal of the Electrochemical Society 2008 155 B869-B876. 

Poltarzewski, E., Stoiti, R, Alderucci, V., Wieczorek, W., and Giordano, N. Nation distribution in gas diffusion electrodes for solid polymer electrolyte membrane fuel cell applications. Journal of the Electrochemical Society 1992 139 761-765. 

Figure 4.1 shows a schematic of a typical polymer electrolyte membrane fuel cell (PEMFC). A typical membrane electrode assembly (MEA) consists of a proton exchange membrane that is in contact with a cathode catalyst layer (CL) on one side and an anode CL on the other side they are sandwiched together between two diffusion layers (DLs). These layers are usually treated (coated) with a hydrophobic agent such as polytetrafluoroethylene (PTFE) in order to improve the water removal within the DL and the fuel cell. It is also common to have a catalyst-backing layer or microporous layer (MPL) between the CL and DL. Usually, bipolar plates with flow field (FF) channels are located on each side of the MFA in order to transport reactants to the... 

T. Erey and M. Linardi. Effects of membrane electrode assembly preparation on the polymer electrolyte membrane fuel cell performance. Electrochimica Acta 50 (2004) 99-105. 

The beginning of modeling of polymer-electrolyte fuel cells can actually be traced back to phosphoric-acid fuel cells. These systems are very similar in terms of their porous-electrode nature, with only the electrolyte being different, namely, a liquid. Giner and Hunter and Cutlip and co-workers proposed the first such models. These models account for diffusion and reaction in the gas-diffusion electrodes. These processes were also examined later with porous-electrode theory. While the phosphoric-acid fuel-cell models became more refined, polymer-electrolyte-membrane fuel cells began getting much more attention, especially experimentally. 

Abstract. The constructive and technological features of silicon electrodes of polymer electrolyte membrane fuel cell (PEMFC) are discussed. Electrodes are made with application of modem technologies of integrated circuits, and technologies of macroporous silicon. Also ways of realization of additional functionalities of electrodes to offered constructive - technological performance are considered. 

Keywords polymer electrolyte membrane fuel cell (PEMFC), porous silicon, silicon electrodes, micro fuel cells. 

Platinum is the most common -and generally accepted as the best- electrode catalyst used in polymer electrolyte membrane fuel cells. However, the sluggish O2 reduction kinetics on the cathode... 

Let us consider the oxygen reduction reaction (ORR) that occurs in the cathode of the polymer electrolyte membrane fuel cell (PEMFC), in an acidic environment. Although a variety of ORR mechanisms have been proposed, the four-electron pathway is primarily used to characterize the behavior of this reaction at a platinum electrode or a glassy carbon electrode coated with a platinum-based catalyst. The overall reaction is given by... 

IV.D.14 Electrodes for Polymer Electrolyte Membrane Fuel Cell Operation on Hydrogen/Air and Reformate/Air... 

Recently, taking advantage of the very narrow size distribution of the metal particles obtained, microemulsion has been used to prepare electrocatalysts for polymer electrolyte membrane fuel cells (PEMFCs) Catalysts containing 40 % Pt Ru (1 1) and 40% Pt Pd (1 1) on charcoal were prepared by mixing aqueous solutions of chloroplatinic acid, ruthenium chloride and palladium chloride with Berol 050 as surfactant in iso-octane. Reduction of the metal salts was complete after addition of hydrazine. In order to support the particles, the microemulsion was destabilised with tetrahydrofurane in the presence of charcoal. Both isolated particles in the range of 2-5 nm and aggregates of about 20 nm were detected by transmission electron microscopy. The electrochemical performance of membrane electrode assemblies, MEAs, prepared using this catalyst was comparable to that of the MEAs prepared with a commercial catalyst. 

Quintus, M, Composite Electrodes and Membranes for Polymer Electrolyte Membrane Fuel Cells, PhD Thesis, University of Stuttgart, 2002, urn nbn de bsz 93-opus-12074 A, Dillon, K,M, Jones, T,A, Bekkedahl, C,H, Kiang, D,S, Bethune, M,J, Heben, Nature 386, 1997,377... 

Fig. 3.5 Schematic cross section of the simplified planar anode-electrode-cathode structure of two typical fuel cells a polymer-electrolyte membrane fuel cell and b solid oxide fuel cell...

For polymer electrolyte membrane fuel cell (PEMFC) applications, platinum and platinum-based alloy materials have been the most extensively investigated as catalysts for the electrocatalytic reduction of oxygen. A number of factors can influence the performance of Pt-based cathodic electrocatalysts in fuel cell applications, including (i) the method of Pt/C electrocatalyst preparation, (ii) R particle size, (iii) activation process, (iv) wetting of electrode structure, (v) PTFE content in the electrode, and the (vi) surface properties of the carbon support, among others. ... 

Chapter 8 is devoted to the simulation of corrosive dissolution of Pt binary nano-cluster in acid environment, of polymer electrolyte membrane fuel cells. It is well known that under the present catalytic electrode production for low temperature fuel cell, it is necessary to reduce their costs by the proposal of binary platinum nanoclusters PtX (where X are the transition metals Cr, Fe, Co, Ni, Ru), while such nanoparticles may possess high... 

The electrochemical reactions occurring at the electrodes of polymer electrolyte membrane fuel cells, as well as the overall current-producing reaction are the same as in the hydrogen-oxygen fuel cells with liquid acidic electrolyte discussed in Section 16.4 (Eqs. 16.2 and 16.3). 

In polymer electrolyte membrane fuel cells, like in many other kinds of fuel cells, gas-diffusion electrodes are used. They consist of a porous, hydrophobic gas-diffusion layer (GDL) and of a catalytically active layer. The diffusion layers (often called backing layers) usually consist of a mixture of carbon black and about 35% by mass of polytetrafluoroethylene (PTFE) applied to a conducting base (most often a thin graphitized cloth). The GDLs yield a uniform supply of reactant gas... 

The electrode reactions in polymer electrolyte membrane fuel cells proceed within the active layer along a highly developed catalyst-electrolyte-gas three-phase boundary. The active layer is supported either by a special support (carbon cloth or carbon paper made hydrophobic) or by the membrane itself. 

For reasons that are discussed in Section 19.4, the catalyst for the hydrogen electrode in polymer electrolyte membrane fuel cells is a mixed platinum-ruthenium catalyst applied to carbon black, rather than pure platinum. The overall thickness of modern MEA is about 0.5-0.6mm (of which 0.1 mm for the membrane, for each of the two GDLs, and for each of the two active layers). The bipolar plates have a thickness of about 1.5 mm, the channels on both sides having a depth of about 0.5 mm. 

Modern polymer electrolyte membrane fuel cell stacks are basically intended for high energy densities at the electrodes (up to 0.6 W/cm ). For this reason, and also because of the compact design, the maximum values of the stacks specific power per unit volume and weight are higher for them, than for all other batteries of conventional type. Often, polymer electrolyte membrane fuel cells are used as well for operation at lower energy densities. 

A detailed cost analysis for a polymer electrolyte membrane fuel cell power plant of 5 kW was provided in 2006 by Kamarudin et al. According to their data, the total cost of such a plant will be about 1200 of which 500 is for the actual fuel-cell stack and 700 for the auxiliary equipment (pumps, heat exchangers, etc.). The cost of the fuel-cell stack is derived from the components as 55 /kW for the membranes, 52 /kW for the platinum, 128 /kW for the electrodes, and 148 /kW for the bipolar plates. 

The peripheral equipment needed for direct methanol fuel cells is largely analogous to that of polymer electrolyte membrane fuel cells. The mechanical basis of fuel cells and stacks on the whole consists of bipolar plates between which the sandwiched membrane-electrode assemblies are arranged. For the venting of heat, cooling plates with a circulating heat transfer agent are set up in a particular order between individual fuel cells in the stack. 

Considerable changes are needed in the anodic part of the membrane-electrode assemblies in order to accommodate the first two of the above-mentioned points. Instead of the porous gas diffusion layer that in polymer electrolyte membrane fuel cells ensures a uniform distribution of hydrogen across the surface, a gas-liquid diffusion layer that contains a set of hydrophilic as well as a set of hydrophobic pores is needed here. Through the hydrophilic pores, this layer must secure the unobstructed access of the aqueous methanol solution to the reaction zone and its uniform distribution. Through the hydrophobic pores, this layer must secure the unobstructed elimination of carbon dioxide, as the gaseous reaction product, from the reaction zone. Analogous changes must be made in the catalytically active anode layer of the membrane-electrode assemblies, where the gas is actually formed, and must be removed toward the gas-liquid diffusion layer. 

Bipolar graphite plates having special channels for reactant supply and distribution over the entire electrode surface, which are now widely used in polymer electrolyte membrane fuel cell stacks, were for the first time used in phosphoric acid fuel cells. 

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