Polymer electrolyte membrane processes

Helmer-Metzmann, R, Osan, R, Schneller, A., Ritter, H., Ledjeff, K., Nolte, R. and Thorwirth, R. 1993. Polymer electrolyte membrane and process for its manufacture. E. Patent 0 574 791 A2. 

M. Schulze, N. Wagner, T. Kaz, and K. A. Friedrich. Gombmed electrochemical and surface analysis investigation of degradation processes in polymer electrolyte membrane fuel cells. Electrochimica Acta 52 (2007) 2328-2336. 

Under normal operation of an H2/O2 fuel cell, anodic oxidation of IT2 (or other hydrocarbons or alcoholic fuels)—that is, H2 —> 2H+ -1- 2e —produces protons that move through the polymer electrolyte membrane (PEM) to the cathode, where reduction of O2 (i.e., O2 -1- 2H+ -1- 2e —> H2O) produces water. The overall redox process is H2 -1-O2 —> H2O. The electronically insulating PEM forces electrons produced at the anode through an external electric circuit to the cathode to perform work in stationary power units, drive trains... 

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. 

Unlike alkaline, phosphoric acid, and polymer electrolyte membrane fuel cells, MCFCs don t reguire an external reformerto convert more energy-dense fuels to hydrogen. Due to the high temperatures at which they operate, these fuels are converted to hydrogen within the fuel cell itself by a process called internal reforming, which also reduces cost. 

In PEMFC systems, water is transported in both transversal and lateral direction in the cells. A polymer electrolyte membrane (PEM) separates the anode and the cathode compartments, however water is inherently transported between these two electrodes by absorption, desorption and diffusion of water in the membrane.5,6 In operational fuel cells, water is also transported by an electro-osmotic effect and thus transversal water content distribution in the membrane is determined as a result of coupled water transport processes including diffusion, electro-osmosis, pressure-driven convection and interfacial mass transfer. To establish water management method in PEMFCs, it is strongly needed to obtain fundamental understandings on water transport in the cells. 

Polymer electrolyte fuel cell (PEFC) is considered as one of the most promising power sources for futurist s hydrogen economy. As shown in Fig. 1, operation of a Nation-based PEFC is dictated by transport processes and electrochemical reactions at cat-alyst/polymer electrolyte interfaces and transport processes in the polymer electrolyte membrane (PEM), in the catalyst layers consisting of precious metal (Pt or Ru) catalysts on porous carbon support and polymer electrolyte clusters, in gas diffusion layers (GDLs), and in flow channels. Specifically, oxidants, fuel, and reaction products flow in channels of millimeter scale and diffuse in GDL with a structure of micrometer scale. Nation, a sulfonic acid tetrafluorethy-lene copolymer and the most commonly used polymer electrolyte, consists of nanoscale hydrophobic domains and proton conducting hydrophilic domains with a scale of 2-5 nm. The diffusivities of the reactants (02, H2, and methanol) and reaction products (water and C02) in Nation and proton conductivity of Nation strongly depend on the nanostructures and their responses to the presence of water. Polymer electrolyte clusters in the catalyst layers also play a critical... 

Figure 3.5. Process diagram of alkaline electrolysis for the production of H2 Polymer Electrolyte Membrane (PEM) Electrolysis...

Jiao K, Li X (2009) Three-dimensional multiphase modeling of cold start processes in polymer electrolyte membrane fuel cells. Electrochim Acta 54 6876-6891 Bar-On I, Kirchain R, Roth R (2002) Technical cost analysis for PEM fuel cells. J Power Sources 109 71-75... 

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. ... 

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