Hydrogen oxidation reaction membrane resistance

In this section, we construct several analytical polarization curves of PEMFCs and high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). In these types of cell, owing to the excellent kinetics of the hydrogen oxidation reaction, the polarization voltage of the anode is negHgible. The voltage loss in a PEMFC is determined by the oxygen transport, ORR kinetics, and the cell resistivity. 

The opposing reactant contactor mode applies to both equilibrium and irreversible reactions, if the reaction is sufficiently fast compared to transport resistance (diffusion rate of reactants in the membrane). This concept has been demonstrated experimentally for reactions requiring strict stoichiometric feeds, such as the Claus reaction, or for kinetically fast, strongly exothermic heterogeneous reactions, such as partial oxidations. Triphasic (gas/liquid/solid) reactions, which are limited by the diffusion of the volatile reactant (e.g., olefin hydrogenation), can also be improved by using this concept. 

Similar TS-1 films have been applied for phenol hydroxyl-ation reaction to dihydroxybenzenes (hydroquinone and catechol) [354] and catalytic oxidation of styrene to benzaldehyde and phenylacetaldehyde [355] with hydrogen peroxide as oxidant in batch-type membrane reactors. The dihydroxybenzenes and phenylacetaldehyde selectivity values increased with in-framework Ti content. In order to reduce the TS-1 membrane costs, Chen et al. [356] have successMly synthesized TS-1 on mullite tubes by replacing TPAOH with TPABr/EtjNH system (4% of the initial cost). The catalytic activity was tested in the probe reaction of isopropyl alcohol oxidation with hydrogen peroxide under pervaporation condition at 60°C. In general, future work on TS-1 film catalysts is required to improve mass transfer resistances and reaction conversion without compromising selectivity. 

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