Ionomer-free

An anode configuration closely related to the AB approach is the so-called reconfigured anode, in which a thin layer of metal (such as Pt/C) or metal oxide (such as FeOx) is added to the outside of the anode GDL facing the flow field. - Unlike a normal anode electrode layer that is impregnated with ionomers for facile proton transport, this ionomer-free CO oxidation layer is hydrophobic for improved gas diffusion to help maximize the interaction between CO and O2. 

Thus far we have not succeeded in the isolation of an ionomer free of impurities from a solvent favoring polyelectrolyte behavior where its solution behavior can be compared to that in Table II. Currently such studies are in progress. 

Although the exact proton conduction mechanism on the ionomer-free Pt surface of NSTF remains unclear, it is apparent that the conductivity is strongly dependent on water content [82, 121] It is conceivable that one could achieve higher proton conductivity under a dry operating condition if one improved the water-holding and/ or water-adsorption capabilities at the Pt surface. In one attempt, highly hydrophilic... 

As for the first assumption, the electrolyte phase must be treated as a mixed phase. It consists of a thin-film structure of ionomer at the surface of Pt/C agglomerates and of water in ionomer-free intra-agglomerate pores. The proton density is highest at the ionomer film (pH 1 or smaller), and it is much smaller in water-filled pores (pH > 3). However, the proton density distribution is not incorporated in the statistical utilization Tstat, but in an agglomerate effectiveness factor, defined in the section Hierarchical Model of CCL Operation. ... 

The importance of proton distribution and transport in water-filled nanopores with charged metal walls is most pronounced in ionomer-free UTCLs (type II electrodes), cf. the main case considered in this section. In either type of CLs, proton and potential distribution at the nanoscale are governed by electrostatic phenomena. 

FIGURES.22 An illustration of design and key properties of ionomer-free ultrathin catalyst layers with insulating or electronically conductive support materials. The typical thickness is in the range of 200 nm. 

Chan, K. and Eikerling, M. 2011. A pore-scale model of oxygen reduction in ionomer-free catalyst layers of PEFCs. LEl twchenL So., 158( 1), B18-B28. 

Moving up the scale to the level of flooded nanoporous electrodes, Michael s group has developed the first theoretical model of ionomer-free ultrathin catalyst layers—a type of layer that promises drastic savings in catalyst loading. Based on the Poisson-Nernst-Planck theory, the model rationalized the impact of interfacial charging effects at pore walls and nanoporosity on electrochemical performance. In the end, this model links fundamental material properties, kinetic parameters, and transport properties with current generation in nanoporous electrodes. 

Pichonat T, Ganthier-Manuel B. Porons silicon-based ionomer-free membrane electrode assembly for miniature fuel cells. Fuel Cell 2006 6(5) 323—5. 

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