Cathode catalyst layer operation standard

Tsushima et al. (2010) developed an MRI system to investigate the effects of relative humidity (RH) and current density on the transverse water content profile in a membrane under fuel cell operation at a practical PEMFC operating temperature. The MRI visualization revealed that in dry conditions (40% RH), the membrane hydration X number was 3, and the water content profile in the membrane was fiat because the diffusion process in the membrane was dominant in the water transport. In a standard condition (80% RH) the water content in the membrane was 8, and a partial dehydration at the anode was observed at a current density of 0.2 A/cm, indicating that electroosmosis was influential. At the higher RH level of 92%, the water content X within the membrane at 0.2 A/cm was around 22, corresponding to the eqnilibrium state of the membrane in liquid water, and the water content profile with the increase in current density became fiat. This indicates that the liquid water generated in the cathode catalyst layer permeated the membrane, where water transport plays a more dominant role. 

FIGURE 13.15 Schematic illustrations of a standard NSTF cathode (a) and various approaches (b, c, and d) demonstrated in Ref. [122] to improve the fuel cell operational robustness of NSTF. (b) NSTF cathode was coated with 4-nm-thick ionomer. (c) NSTF cathode was decorated with lOnm silica particles, (d) A few-micron-thick dispersed-catalyst layer was located adjacent to NSTF cathode. Reprinted with permission from Ref. [122]. ECS. (See insert for color representation of the figure.)... 

Durability work has demonstrated the detrimental effects of potential cycling on carbon corrosion (Borup et al., 2007) and Pt particle growth and movement of the support within the catalyst layer are two identified mechanisms of deterioration (Ferreira et al., 2005 Kara et al, 2012 Meier et al, 2012a 2012b Wilson et al, 1993). In particular, the corrosion of the carbon black support for cathode catalysts may be a critical problem for cell durability under certain PEMFC operating conditions. The standard electrode potential for the oxidation of carbon to carbon dioxide is low ... 

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