Water sorption Gibbs energy

Kulik, D. A., 2002, Gibbs energy minimization approach to model sorption equilibria at the mineral-water interface Thermodynamic relations for multi-site-surface complexation. American Journal of Science 302,227-279. ... 

Gibbs free energies of water sorption, AG "(/l), can be extracted from isopiestic vapor sorption isotherms this analysis shows that AG (T) < AG", where AG" = -44.7 kj moH is the Gibbs free energy for vapor sorption at a free water surface at ambient condihons. Water absorbed by the membrane is therefore more strongly bound than water at a free bulk water surface this affirms the hydrophilic nature of water sorption in PEMs. 

Gibbs free energy of water sorption by Nation 117. Comparison of energies obtained from sorption isotherms (solid line), corresponding to Figure 6.10(a), and from capillary isotherms (dashed line), corresponding to Figure 6.10(b). 

Moreover, isopiestic water sorption data and dynamic vapor sorption (Soboleva et al., 2011) provide information on water uptake as a function of relative humidity in the surrounding gas phase. This information, if combined with pore size distribution data, could help determine the wetting angle in pores or the Gibbs energy of water sorption as functions of pore size. 

To build a model of water sorption and swelling in PEMs, three microscopic equilibrium conditions of water must be accounted for in the PEM and the adjacent medium. The global equilibrium state corresponds to the minimum of the appropriate thermodynamic free energy, in this case the Gibbs energy. 

For the sorption isotherm, the Gibbs energy of water sorption AG is computed from the thermodynamic relation... 

Vaporization is an activated process controlled by the Gibbs energy of water sorption, which determines (c (iJpem))- Condensation is a kinetic process with a rate proportional to the vapor pressure P" at the interface between PEM and flow chamber. The vaporization exchange rate constant has a physical meaning similar to the exchange current density in electrochemical kinetics, and P"- (c (t, Ipem)) — P" acts like an overpotential of the vaporization process. 

Gibbs energy of water sorption at free water surface (kj mol ) Enthalpy change in the reaction (J mol )... 

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