Role of water in proton conductance

Role of Water in Proton Conductance across Model and Biological Membranes... 

Notwithstanding the non-specific role of water in many non-aqueous solutions, in some cases it may have specific effects due to ion-water interactions which depend on the particular nature of the ions and solvent. Thus the conductance of associated AgNOa and (CHajaTlI in dimethyl-formamide increase with the water content in contrast to the decrease found for dissociated salts In methanol and ethanol the conductance of perchloric acid (and presumably of other Inorganic acids) decreases significantly upon addition of 0.3 % water. This was attributed to a change in the proton transport mechanism. 

Electrochemistry has elucidated the role of water in the deposition of polypyrrole [216]. The favourable effect of water [217] was found to be due to its protonscavenging action which eliminates protonation of pyrrole (protons are released in coupling) and its consequent subtraction from oxidation. The effect of the counteranion on structure and conductivity properties of polypyrrole is well documented [98,215,217-25]. It was found that deposition from carboxylate anions of different basicity [223] produces polymers with a conductivity which increases as the anion basicity is decreased. Sulfonate anions produce the... 

The microstructure of a catalyst layer is mainly determined by its composition and the fabrication method. Many attempts have been made to optimize pore size, pore distribution, and pore structure for better mass transport. Liu and Wang [141] found that a CL structure with a higher porosity near the GDL was beneficial for O2 transport and water removal. A CL with a stepwise porosity distribution, a higher porosity near the GDL, and a lower porosity near the membrane could perform better than one with a uniform porosity distribution. This pore structure led to better O2 distribution in the GL and extended the reaction zone toward the GDL side. The position of macropores also played an important role in proton conduction and oxygen transport within the CL, due to favorable proton and oxygen concentration conduction profiles. 

Abstract Chemical structure, polymer microstructme, sequence distribution, and morphology of acid-bearing polymers are important factors in the design of polymer electrolyte membranes (PEMs) for fuel cells. The roles of ion aggregation and phase separation in vinylic- and aromatic-based polymers in proton conductivity and water transport are described. The formation, dimensions, and connectivity of ionic pathways are consistently found to play an important role in determining the physicochemical properties of PEMs. For polymers that possess low water content, phase separation and ionic channel formation significantly enhance the transport of water and protons. For membranes that contain a high... 

In this section, we describe the role of fhe specific membrane environment on proton transport. As we have already seen in previous sections, it is insufficient to consider the membrane as an inert container for water pathways. The membrane conductivity depends on the distribution of water and the coupled dynamics of wafer molecules and protons af multiple scales. In order to rationalize structural effects on proton conductivity, one needs to take into account explicit polymer-water interactions at molecular scale and phenomena at polymer-water interfaces and in wafer-filled pores at mesoscopic scale, as well as the statistical geometry and percolation effects of the phase-segregated random domains of polymer and wafer at the macroscopic scale. 

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