Acid doping hydration

Winokur, M.J. and B.R. Mattes. 1998. Structural studies of halogen acid doped polyaniline and the role of water hydration. Macromolecules 31 8183. 

The In(I/PH2o) versus HT is plotted in Fig. 20 for acid concentration around 100% and for all three acid doped PBI/PPy(50)co PSF 50/50, Copolymer II and for hquid phosphoric acid. The lesnlting hydration enthalpies are shown in Table 4. The hydration enthalpy depends significantly on the chemical stractnre of the polymer matrix and differs from that of pure phosphoric acid. The H3PO4 doped Copolymer II shows the highest hydration enthalpy valnes compared to the other two systems showing strong interaction with the water molecnles. 

In all cases, the values of hydration enthalpy of the acid doped polymers reported in Table 4 are maity times higher than those reported for phosphoric acid in other references. This fact strongly suggests the positive effect of the polymer matnx on the ability of the membrane/ phosphoric acid system to absorb and retain water. 

The equilibrium hydration level depends both on temperature and on steam partial pressure. The water generated at the cathode and the extent to which it equilibrates in the membrane may vary between the different polymer electrolytes, then-acid doping level, and the preparation method of the electrolyte, e.g., the solvent used for the... 

Figure 23.10 Proton conductivity of a few prototypical proton conducting separator materials Nafion as a representative of hydrated acid ionomers (see also Fig. 23.2(a) [43, 78], a complex of PBI (polybenzimidazole) and phosphoric acid as a representative of adducts of basic polymers and oxo-acids (see also Fig. 23.2(b)) [16], phosphonic acid covalently immobilized via an alkane spacer at a siloxane backbone (see also Fig. 23.2(c)) [127], the acid salt CsHSO, [125] and an Y-doped BaZrOj [126].

The same experiment was carried out for Copolymer IIx (x = 60, Fig. 10) in order to investigate the effect of the polymer matrix of the add doped samples on the hydration of the content phosphoric acid and the retention of water nnder specified conditions In this case also, the two regions are distmgnished as can be seen in Fig. 18. Above the border line in regions II the hydration level of the system can be defined as ... 

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