Polymer electrolyte fuel cell Porous

Bolwin, K., Giilzow, E., Bevers, D., and Schnurnberger, W. Preparation of porous electrodes and laminated electrode-membrane structures for polymer electrolyte fuel cells (PEFCs). Solid State Ionics 1995 77 324-330. 

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. 

Figure 13.9 Schematic diagram of a polymer electrolyte fuel cell (A) gas manifolding, (B) porous graphite block, (C) active catalyst layer (dispersed Pt and Teflon binder), and (D) polymer electrolyte.

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... 

Pasaogullari, U. and Wang, C.-Y., Two-phase transport and the role of micro-porous layer in polymer electrolyte fuel cells, Electrochim. Acta, 49, 4359, 2004. 

Polymer-electrolyte fuel cells (PEFC and DMFC) possess a exceptionally diverse range of applications, since they exhibit high thermodynamic efficiency, low emission levels, relative ease of implementation into existing infrastructures and variability in system size and layout. Their key components are a proton-conducting polymer-electrolyte membrane (PEM) and two composite electrodes backed up by electronically conducting porous transport layers and flow fields, as shown schematically in Fig. 1(a). 

K.-B. Min, S. Tanaka, and M. Esashi, Fabrication of novel MEMS-based polymer electrolyte fuel cell architectures with catalytic electrodes supported on porous SiOj, Journal of Micromechanics and Microengineering, 16 (2006) 505-511. 

Wang, X., Zhang, H., Zhang, J. etal (2006) Investigation of the role of the micro-porous layer in polymer electrolyte fuel cells with hydrogen deuterium contrast neutron radiography. J. Power Sources, 162, 474-479. 

Nakajima H, Konomi T and Kitahara T (2007), Direct water balance analysis on a polymer electrolyte fuel cell (PEFC) Effects of hydrophobic treatment and micro-porous layer addition to the gas diffusion layer of a PEFC on its performance during a simulated start-up operation. Journal of Power Sources, 171, 457-463. 

This method was also applied by other authors to hydrogen absorption in a porous electrode consisting of spherical particles of ABs-type material [458] to describe a whole polymer electrolyte fuel cell with gas diffusion in pores [459], alkaline fuel cells [460], and intercalation electrodes [461]. Several authors attempted to fit the experimental impedances to their models [456-461]. 

Wang, Y. (2009) Porous-media flow fields for polymer electrolyte fuel cells, I. Low humidity operation. J. Electrochem. Soc., 156 (10), B1124-B1133. 

Wang, Y. (2009) Porous-media flow fields for polymer electrolyte fuel cells,... 

Min K, Tanaka S, Esashi M (2003) Silicon-based micro-poljnner electrolyte fuel cells. In IEEE intemational conference on micro electro mechanical systems, Kyoto Min K, Tanaka S, Esashi M (2006) Fabrication of novel MEMS-based polymer electrolyte fuel cell architectures with catalytic electrodes supported on porous Si02- J Micromech Microeng 16 505-511 Miu M, Danila M, Ignat T, Craciunoiu F, Kleps I, Simion M, Bragam A, Dinescu A (2009) Metallic-semiconductor nanosystem assembly for miniaturized fuel cell applications. Superlatt Microstmct 46 291-296... 

Polymer Electrolyte Fuel Cells (PEFCs), Introduction, Fig. 3 Simplified scheme with an acidic solid polymer electrolyte, e.g., the polymer electrolyte fuel cell PEFC). Fuel, H2 Oxidant, O2. Only porous gas diffusion electrodes and electrolyte are shown cell housing is not shown [12]... 

Figure 8.1. Outline of the general framework for structure-based modeling of catalyst layer operation in polymer electrolyte fuel cells [51], (Reprinted from Elecfrochimica Acta 53.13, Liu J, Eikerling M. Model of cathode catalyst layers for polymer electrolyte fuel cells The role of porous structure and water accumulation, 4435-46, 320 08, with permission from Elsevier.)...

Lindstrom RW, Kortsdottir K, Wesselmark M et al (2010) Active area determination of porous Pt electrodes used in polymer electrolyte fuel cells temperature and humidity effects. J Electrochem Soc 157 B1795-B1801... 

Abstract The polymer electrolyte fuel cell (PEFC) consists of disparate porous media microstructures, e.g. catalyst layer, microporous layer, gas diffusion layer, as the key components for achieving the desired performance attributes. The microstmcture-transport interactions are of paramount importance to the performance and durability of the PEFC. In this chapter, a systematic description of the stochastic micro structure reconstmction techniques along with the numerical methods to estimate effective transport properties and to study the influence of the porous structures on the underlying transport behavior is presented. 

Akey performance limitation in the polymer electrolyte fuel cell (PEFC) originates from the multiple, coupled and competing, transport interactions in the constituent porous components. The suboptimal transport behavior resulting from the underlying complex and multifunctional microstmctures in the catalyst layer (CL), gas diffusion layer (GDL) and microporous layer (MPL) leads to water and thermal management issues and undesirable performance loss. Therefore, it is imperative to understand the profoimd influence of the disparate porous microstmctures on the transport characteristics. In this chapter, we highhght the stochastic microstmcture reconstmction technique and direct transport simulation in the CL, GDL and MPL porous stmctmes in order to estimate the effective transport properties and imderstand the microstmctural impact on the imderlying transport behavior in the PEFC. 

K. Kang and H. Ju, Numerical modeling and analysis of micro-porous layer effects in polymer electrolyte fuel cells , J. Power Sources, 194, 763 (2009). 

If we speak specifically about polymer electrolyte fuel cells (PEFCs), to which this book is devoted, the theory of the polymer electrolyte membrane is the theory of proton transport in a complex water-containing porous environment it is also the story of water in the membrane, of its sorption and distribution coupled with the proton transport. 

As illustrated in Figure 1.2, one side of the cathode GDL facing to the catalyst layer is generally provided with a micro-porous layer (MPL) of polytetrafluoroethylene (PTFE) with hydrophobic characteristics. It has much smaller pores and a much smoother surface than the GDL. The MPL plays an important role in the water management of polymer electrolyte fuel cells however, details of the meehanism that works to suppress water flooding are not fully understood. Questions still remain about whether the water transfer in the MPL occurs in the liquid or vapor phase. 

---