Polymer electrolyte membrane structure

Antoine et al. [28] inveshgated the gradient across the CL and found that the Pt utilization was dependent on the CL porosity. In a nonporous CL, catalyst utilization was increased through the preferential locahon of Pt close to the gas diffusion layer in a porous CL, catalyst utilization efficiency was increased through the preferential location of Pt close to the polymer electrolyte membrane. In PEM fuel cells, fhe CL has a porous structure, and better performance is expected if higher Pf loading is used af preferential locahons close to the membrane/catalyst layer interface. 

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. 

Schematic depiction of the structural evolution of polymer electrolyte membranes. The primary chemical structure of the Nafion-type ionomer on the left with hydrophobic backbone, side chains, and acid head groups evolves into polymeric aggregates with complex interfacial structure (middle). Randomly interconnected phases of these aggregates and water-filled voids between them form the heterogeneous membrane morphology at the macroscopic scale (right).

Physical models of fuel cell operation contribute to the development of diagnoshc methods, the rational design of advanced materials, and the systematic ophmization of performance. The grand challenge is to understand relations of primary chemical structure of materials, composition of heterogeneous media, effective material properties, and performance. For polymer electrolyte membranes, the primary chemical structure refers to ionomer molecules, and the composition-dependent phenomena are mainly determined by the uptake and distribuhon of water. 

M. Eikerling, A. A. Kornyshev, and E. Spohr. Proton-conducting polymer electrolyte membranes Water and structure in charge. Advances in Polymer Science 215 (2008) 15-54. 

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. 

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... 

In a H2/air fuel cell, the protons produced at the anode side need to be transferred to the cathode side to react with 02. This requires a proton transport electrolyte. Nafion membranes, composed of a perfluorosulfonated polymer, are the most commonly used polymer electrolyte membranes to conduct protons. The structure of the Nafion membrane is shown in Figure 1.5. Nafion can take on a... 

The fuel solution is fed into the anode side channel. Methanol reacts at the anode and releases electrons, protons, and carbon dioxide. At the cathode, molecnlar oxygen reacts with proton being transported throngh the PEM (Polymer Electrolyte Membrane) from the anode and prodnces water. The electrons travel throngh the external circnit to the cathode. Power generation is performed by the above oxidation-rednction reaction principles. In order to realize micro-mini power sonrces, large nnmbers of DMFC shonld be integrated serially on a substrate. The structure of the proposed DMFC is suitable for this application. 

Fig. 5 Schematic cross section of the simplified planar anode-electrode-cathode structure of two typical fuel cells a polymer-electrolyte membrane fuel ceU and b solid oxide fuel cell. See Color Plates...

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. ... 

The fuel cell has a proven history with solid oxide based systems. Recent needs for miniaturization have generated new ideas of fuel sources and structures. These include direct methanol fuel cells (DMFCs) and polymer electrolyte membrane fuel cells (PEMFCs). These fuel cells have advantages over others for several reasons. A key quality is the potential energy that the fuel sources provide with respect to the fuel costs. 

Qiao, J., Fu, J., Lin, R., Ma, J., Liu, J., 2010. AUcaUne solid polymer electrolyte membranes based on structurally modified PVA/PVP with improved alkali stability. Polymer 51,4850-4859. 

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