Bipolar plates acid uptake

The carbon or graphite type also mainly determines the properties of the bipolar plate like porosity, phosphoric acid uptake, and hydrophobicity, both regarding the surface and the bulk. For the HT-PEM fuel cell technology, preferred configurations are hydrophobic structures with low phosphoric acid uptake. 

HT-PEM fuel cells operate with phosphoric acid doped polymer membrane as electrolyte. The acid is physically adsorbed to the membrane. The phosphoric acid distribution within the fuel cell components, such as membrane, catalyst layers, microporous layer, gas diffusion layers, and bipolar plates, is known to be a critical parameter for performance and life time of this type of fuel cells [10]. There are no defined specifications about phosphoric acid uptake of the bipolar plate because its impact on the fuel cell performance strongly depends on several parameters and always has to be considered in a context of the overall fuel cell design. 

Eisenhuth has characterized different bipolar plates with respect to their acid uptake. In general, a low acid uptake, corresponding to a high hydrophobicity, is desired in order to keep the acid management in the overall cell under... 

Fig. 19.9 Phosphoric acid uptake in different bipolar plates after >3000 h HT-PEM fuel cell stack operation. The samples based on PPS and PVDF contained the same type of synthetic graphite, whereas the sample called...

Table 22.8 Acid uptake (sum of cathode and anode) of different bipolar plate materials at the EoL relative to the phosphoric acid content of the system at the BoL [93], with permission of International Electrochemistry Society...

---