Catalyst polymer electrolyte membrane fuel cells

Electro-catalysts which have various metal contents have been applied to the polymer electrolyte membrane fuel cell(PEMFC). For the PEMFCs, Pt based noble metals have been widely used. In case the pure hydrogen is supplied as anode fuel, the platinum only electrocatalysts show the best activity in PEMFC. But the severe activity degradation can occur even by ppm level CO containing fuels, i.e. hydrocarbon reformates[l-3]. To enhance the resistivity to the CO poison of electro-catalysts, various kinds of alloy catalysts have been suggested. Among them, Pt-Ru alloy catalyst has been considered one of the best catalyst in the aspect of CO tolerance[l-3]. 

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. 

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. 

Cho, Y. H., Park, H. S., Cho, Y. H., Jung, D. S., Park, H. Y, and Sung, Y. E. Effect of platinum amount in carbon supported platinum catalyst on performance of polymer electrolyte membrane fuel cell. Journal of Power Sources 2007 172 89-93. 

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... 

Polymer Electrolyte Membrane Fuel Cell (PEMFC) expensive catalysts required operates best at 60—90 °C... 

There are a few distinct structural concepts for high-performance Pt alloy ORR electrocatalysts that are currently attracting much attention because they hold the promise of significant activity improvements compared to pure Pt catalysts. As a result of this, these electrocatalysts potentially offer the prospect to impact the future of Polymer Electrolyte Membrane fuel cell catalyst technology. 

The anode layer of polymer electrolyte membrane fuel cells typically includes a catalyst and a binder, often a dispersion of poly(tetraflu-oroethylene) or other hydrophobic polymers, and may also include a filler, e.g., acetylene black carbon. Anode layers may also contain a mixture of a catalyst, ionomer and binder. The presence of a ionomer in the catalyst layer effectively increases the electrochemically active surface area of the catalyst, which requires a ionically conductive pathway to the cathode catalyst to generate electric current (16). 

The SECM capacity for rapid screening of an array of catalyst spots makes it a valuable tool for studies of electrocatalysts. This technique was used to screen the arrays of bimetallic or trimetallic catalyst spots with different compositions on a GC support in search of inexpensive and efficient electrocatalytic materials for polymer electrolyte membrane fuel cells (PEMFC) [126]. Each spot contained some binary or ternary combination of Pd, Au, Ag, and Co deposited on a glassy carbon substrate. The electrocatalytic activity of these materials for the ORR in acidic media (0.5 M H2S04) was examined using SECM in a rapidimaging mode. The SECM tip was scanned in the x—y plane over the substrate surface while electrogenerating 02 from H20 at constant current. By scanning... 

Alkaline fuel cells (AFC) — The first practical -+fuel cell (FC) was introduced by -> Bacon [i]. This was an alkaline fuel cell using a nickel anode, a nickel oxide cathode, and an alkaline aqueous electrolyte solution. The alkaline fuel cell (AFC) is classified among the low-temperature FCs. As such, it is advantageous over the protonic fuel cells, namely the -> polymer-electrolyte-membrane fuel cells (PEM) and the - phosphoric acid fuel cells, which require a large amount of platinum, making them too expensive. The fast oxygen reduction kinetics and the non-platinum cathode catalyst make the alkaline cell attractive. 

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... 

In June 2001 we initiated this project to explore the possibilities of decreasing the Pt loading in Pt-Ru catalysts for H2/CO oxidation in the polymer electrolyte membrane fuel cells (PEMFCs). We have demonstrated a new method for the preparation of the Pt-Ru catalysts involving spontaneous deposition of Pt on Ru nanoparticles that we explored first with single crystal Ru surfaces. The resulting catalysts have a high CO tolerance with considerably lower Pt loading than the commercial catalysts. 

Polymer electrolyte membrane fuel cells operate at relatively low temperatures, around 80°C. Low temperature operation allows them to start quickly (less warm-up time) and results in better durability. However, it requires that a noble-metal catalyst (typically platinum) be used to separate the hydrogen electrons and protons. The platinum catalyst is also extremely... 

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. 

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. ... 

M. Lefevre, J. Dodelet, Fe-based catalysts for the reduction of oxygen in polymer electrolyte membrane fuel cell conditions determination of the amount of peroxide released during electroreduction and its influence on the stability of the catalysts, Electrochim. Acta 48 (2003) 2749-2760. 

Another system, where catalytic active oxide particles might lead to a new development, is the polymer electrolyte membrane fuel cell (PEMFC). This t5rpe of fuel cell preferentially works with platinum and platinum alloy catalysts. The development of an effective oxide catalyst could solve some of the problems connected with the application of these systems. 

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. 

Corrosion of the plates not only detracts from their mechanical properties but also gives rise to undesirable corrosion products, namely, heavy-metal ions, which, when depositing on the catalysts, strongly depress their activity. The corrosion processes also give rise to superficial oxide films on the metal parts, and these cause contact resistance of the surfaces. For a lower contact resistance, metallic bipolar plates sometimes have a surface layer of a more stable metal. Thus, in the first polymer electrolyte membrane fuel cell, developed by General Electric for the Gemini spacecraft, the bipolar plates consisted of niobium and tantalum coated with a thin layer of gold. A bipolar plate could also be coated with a layer of carbide or nitride. 

At present, most of the work toward building methanol fuel cells relies on technical and design principles, developed previously for polymer electrolyte membrane fuel cells. In both kinds of fuel cells, it is common to use platinum-ruthenium catalysts at the anode and a catalyst of pure platinum at the cathode. In the direct methanol fuel cells, the membrane commonly used is of the same type as in the hydrogen-oxygen fuel cells. The basic differences between these versions are discussed in Section 19.7. 

Basically, the construction of phosphoric acid fuel cells differs little from what was said in Section 20.4 about fuel cells with a liquid acidic electrolyte. In the development of phosphoric acid fuel cells and, two decades later, in the development of polymer electrolyte membrane fuel cells many similar steps can be distinguished, such as the change from pure platinum catalysts to catalysts consisting of highly disperse platinum deposited on a carbon support with a simultaneous gradual reduction... 

Soboleva T, Zhao X, Malek K, Xie Z, Navessin T, Holdcroft S (2010) On the micro-, meso-, and macroporous structures of polymer electrolyte membrane fuel cell catalyst layers. ACS Appl Mater Interfaces 2 375-384... 

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