Ultra-thin Two-phase Catalyst Layers

The alternative is to fabricate CCLs as ultrathin two-phase composites 100 mn -200 mn), in which electroactive Pt could form the electronically conducting phase, or Pt nanoparticles could be supported on a conductive substrate. The remaining volume should be filled with liquid water, as the sole medium for proton and reactant transport. The ultra-thin two-phase catalyst layer was explored by using the Poisson-Nemst-Planck (PNP) equations as employed for water-filled spherical agglomerates [69, 118]. The equations in Section 8.5.2 can be rewritten for the ID planar situation 

A modified Tafel law can be written for the current-voltage performance 

As an example of how to use the insights conveyed in this chapter we provide an explicit comparison of overall effectiveness of Pt utilization (by atom number or catalyst weight) for conventional 3-phase composite and ultrathin CCLs, in Table 8.2. For conventional catalyst layers, the main detrimental factors arise at the nanoparticle scale and at the macroscopic scale due to triple-phase boundary requirements. For the nanostructured ultrathin CCLs it is assumed that a sputter-deposited continuous Pt layer is needed to provide electronic conductivity. It was suggested in [153] on the basis of cyclic voltammetry measurements that the irregular surface morphology of such catalysts corresponds to grain sizes of 10 nmwith 

---