In this chapter are described the characteristics of transport of hydroxide ions through hydrated polymeric materials with potential application in alkaline fuel cells are described. First, it is made a brief description of anion-exchange membrane fuel cells (AEMFCs), their evolution and key characteristics. Then, this chapter presents a detailed classification of the different types of polymers that have been proposed for AEMFCs and their state of development. After that, mechanisms involved in the transport of hydroxide ions through hydrated anion-exchange membranes are described and discussed, making emphasis in the theoretical approaches applied for their study and their implementation and representability in global transport models. In the final section, it is summarized the key features of the chapter and is made a brief discussion about challenges and future work required for the consolidation of this promising technology.

It is shown that the correct Dulong and Petit law of specific heat can be obtained within a previous generalization of the van der Waals theory which admits the presence of the crystalline state for a simple monatonic substance, if the proper modification of the crystalline mean field is made.

A model for anion-exchange membranes used in alkaline fuel cells was derived based on the thermodynamic of irreversible processes theory. The tests carried out in a simplified fuel cell model included combinations of operation conditions such as feed gases relative humidity, pressure in the electrodes and current density. In general, the membrane model represented well the different transport modes that can occur for wide humidity ranges especially when it is in equilibrium with water vapor, liquid water or both. It was found that the application of pressure gradients to the membrane decreases the water molar flux values through it and small current densities increase them.

Simulations by means of DFT were carried out to represent the structure and morphology of a segment of the anion exchange membrane QSEBS. For three considered structures: tetramethylammonium hydroxide, benzyltrimetylammonium hydroxide and the QSEBS segment, information about spatial distribution, bond distances and total energy was obtained and corroborated with the theoretical study about the degradation of tetramethylammonium hydroxide of reference [1] and the experimental work about the QSEBS membrane of reference [2]. It was found that the obtained structures were in agreement with what is reported in the mentioned studies and what was physically expected.

In this work is presented a kinetic model for the oxygen reduction reaction (ORR), which is studied considering a dissociative mechanism and using electronic structure calculations. This model was developed to include it in a multiscale model for a Proton Exchange Membrane Fuel Cell (PEMFC). As result of this work the energetic properties and electronic structure properties of the system made up by the principal intermediates (O, O2, OH, H2O) and the Pt surface are calculated, also it is obtained the energy barriers for each step and the energy difference between products and reactants, allowing to construct the potential energy surface diagram for the complete oxygen dissociation mechanism. These results point out that the dissociation of adsorbed O2 is the reaction limiting step, it is associated whit the high adsorption energy of this molecule which is explained using electronic structure features as the local density of states. Also the calculated activation energies for the ORR cause an improvement of the phenomenological description of a PEMFC when they are used in a multiscale model.