Thoughts on Ultra Thin Catalyst Layers

The use of porous catalyst layer (CL) is based on the consideration that pores are needed for transporting gaseous reactants and water because a material diffuses much faster through empty space than through liquid or solid materials, and both hydrophobic and hydrophilic pores are needed for transporting gases and water, respectively. Numerous work has been done in order to create and maintain both kinds of pores within the CL, but an ideal situation is not yet achieved. A major problem encountered with such a CL with a thickness around 10 -20 pm is that flooding appears to be unavoidable. In 

It is advantageous to make CLs as thin as possible in order to maximize the catalyst utilization and to reduce the iR loss and the mass transport loss. However, it becomes tricky regarding mass transport loss because if the CL is not severely flooded, it can reduce the mass transport loss, but if a proper water management situation is not achieved thin CL often can be severely or even completely flooded quickly because there is much less space to store water produced at the cathode (we can think the CL as a water reservoir, and a larger one takes longer time to be filled and has more time to send water out to the GDM, and thus it is less likely to be completely flooded). It can be seen from Table 2.11 that a water layer can become hundred times thicker than the CL in 1 second even at a current density as low as 0.1 A cm if none of the water produced at the cathode is removed. Therefore, water management becomes even more crucial and difficult for thin CLs. 

Side view of an ultra thin catalyst layer composed of catalyst-coated nano-columns. 

Since the 3M CL works and is more than 10 times thicker than the ultra thin CL, the ultra thin CL presented here should work and probable be better. 

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