Proton exchange membrane water transport

The electrons released are caught by the carbon cloth or carbon paper, collected by the GDL, conducted to the BP, and led to the external circuit. The protons are caught by the proton exchange membrane and transported to the cathodic side. In the cathodic side, the oxygen provided from BP, protons transferred from the anodic side via the proton exchange membrane, and electrons conducted from the external circuit combine forming water molecules,... 

The heart of the PEM fuel cell is the proton exchange membrane, which transports protons from the anode to the cathode. The membrane also serves to separate the fuel and oxidant gas phases and electronically insulates the cathode from the anode. The most typical membrane is a sulfonated per-fluorinated polymer. The Nation family of membranes made by DuPont is representative of this class, and is based on a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer, with the chemical structure represented in Figure 1.2. The sulfonic acid (SO3H) groups on the side chains allow the protons or other cations to "hop" from one acid site to another, in the presence of water. The exact mechanism of the proton movement is an area of significant research. An active area of research is the development of hydrocarbon-based... 

The most promising fuel cell for transportation purposes was initially developed in the 1960s and is called the proton-exchange membrane fuel cell (PEMFC). Compared with the PAFC, it has much greater power density state-of-the-art PEMFC stacks can produce in excess of 1 kWA. It is also potentially less expensive and, because it uses a thin solid polymer electrolyte sheet, it has relatively few sealing and corrosion issues and no problems associated tvith electrolyte dilution by the product water. 

Siu, A. 2007. Influence of water and membrane morphology on the transport properties of polymers for proton exchange membrane fuel cells. Ph. D. Dissertation, Department of Chemistry, Simon Fraser University. 

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... 

G. J. M. Janssen and M. L. J. Overvelde. Water transport in the proton-exchange-membrane fuel cell Measurements of the effective drag coefficient. Journal of Power Sources 101 (2001) 117-125. 

V. Gurau, M. J. Bluemle, E. S. De Castro, et al. Characterization of transport properties in gas diffusion layers for proton exchange membrane fuel cells. 1. Wettability (internal contact angle to water and surface energy of GDL fibers). Journal of Power Sources 160 (2006) 1156-1162. 

Because of its lower temperature and special polymer electrolyte membrane, the proton exchange membrane fuel cell (PEMFC) is well-suited for transportation, portable, and micro fuel cell applications. But the performance of these fuel cells critically depends on the materials used for the various cell components. Durability, water management, and reducing catalyst poisoning are important factors when selecting PEMFC materials. 

Proton exchange membranes (PEM) fuel cells (or polymer electrolyte fuel cells - PEFCs), with H -conducting polymeric membranes, transports hydrogen (fuel) cations, generated at the anode, to an ambient air exposed cathode, where they are electro-oxidised to water at low temperatures. 

Proton exchange membrane (PEM) fuel cells are the primary choice for transportation systems, but they can also be useful for stationary power production or local hydrogen production. Most of the challenges of PEM fuel cell commercialization center around cost and materials performance in an integrated system. Some specific issues are the cost of catalyst materials, electrolyte performance, i.e., transport rates, and water collection in the gas diffusion layer (GDL). 

Paddison, S.J. Paul, R. Zawodzinski, T.A. A statistical mechanical model of proton and water transport in a proton exchange membrane. J. Electrochem. Soc. 2000, 147 (2), 617-626. 

Operation mode of fuel cell is strongly determined by water balance. Water production by electrochemical process and also water transport due to proton migration and diffusion were measured with use of special complex. For MEA based on MF-4SK proton exchange membrane with hydrophobic catalytic layer an effective water drag coefficient =0.28 for air and =0.53 for pure oxygen, water diffusion coefficient trough membrane T) , =l.55x10 mVs. 

The protons are transported across the proton exchange membrane to the cathode. There they react with oxygen and extract electrons from the cathode to produce water. Besides methanol, also water is consumed at the an-... 

G. J. M. Janssen, A Phenomenological Model of Water Transport in a Proton Exchange Membrane Fuel Cell, Journal of the Electrochemical Society, 148, A1313 (2001). 

Sulfonated Pis with a high proton conductivity and low methanol permeability were tested for their performance as proton exchange membranes in direct methanol fuel cells [58]. The proton to methanol transport selectivity of the membranes correlates well with the self-diffusion coefficients of water in the membranes. The membranes show an improved fuel cell device performance, however the high interfacial resistance between the membranes and electrodes... 

Modroukas D, Calabrese Bartrai S, Modi V, Frechette LG (2005) Water management and mass transport studies. In Free convection proton-exchange membrane fuel cells. In 208th meeting of the electrochemical society, Los Angeles, 16-21 Oct 2005... 

---