Proton transport mechanisms types

Water-based PEMs exhibit proton transport mechanisms and mobilities similar to those in liquid electrolytes like hydrochloric acid proton conductivities could reach up to 0.1 S cm in the case of PFSA-type ionomers, and up to 0.5 S cm in the case of block copolymer systems. The temperature range of operation of PEMs stretches from —30°C to 90°C, the lower bound being determined by the freezing point of water, which is suppressed because of the high surface energy of water in nanopores. The upper limit is determined by evaporation of water only a few water-based PEMs have been demonstrated that could maintain a sufficient conductivity above lOO C. 

Taken together, these results indicate that similar to other proton-translocating membrane proteins, both types of Na /H exchangers contain critical sulfhydryl groups that are involved in the transport mechanism. These sulfhydryl groups do not appear to be present at the external transport site but may be involved in switching from an inactive to an activated state. 

The value of the activation energy of proton transport in well-humidified PEMs, 0.12 suggests that the widely studied relay-type mechanism... 

The last comprehensive review covering proton conductivity and proton conducting materials was written by one of the authors (dating back to 1996) since then, there have been several other review articles of similar scope (e.g., see Colomban ). There are also many reviews available on separator materials used for fuel cells (see articles in refs 3 and 4 and references therein, recent review-type articles, " and a literature survey ), which, more or less, address all properties that are relevant for their functioning in a fuel cell. The transport properties are usually described in these articles however, the treatments are frequently restricted to macroscopic approaches and handwaving arguments about the transport mechanisms. The purpose of the present review is to combine a few recently published results in the context of a discussion of transport phenomena in proton-conducting separator materials, which have some relevance in fuel cell applications (for a more complete list of the comprehensive literature in the field, the interested reader is referred to the aforementioned references). 

Electron transport through oxidases in the plasma membrane contributes to, or controls, part of the proton release from the cell. The details of oxidase function and the mechanism of control remain to be elucidated. The NADPH oxidase of neutrophils is a special case in which proton transport is coupled to the cytochrome >557 electron carrier. This type of proton transport has its precedents in the well-characterized proton pumping through electron carriers in mitochondrial and chloroplast membranes and prokaryotic plasma membranes. 

Delocalized H+ counterions are denoted with a subscript f, while H+ species which transfer between tbe film and bulk solution during the redox reaction are identified by the subscripts s. Thus, for each electron injected into the film there is a simultaneous transfer of one proton, i.e. Hs +, from the solution bulk into the hydrous oxide material, while at the same time there is a transfer locally of 1.5 protons into the ligand sphere of the central metal ion for each electron added to the latter. Proton transport is likely to occur via a Grotthus-type mechanism in these films and is much more likely than OH movement as suggested by other authors [144]. 

In eukaryotic cells aerobic metabolism occurs within the mitochondrion. Acetyl-CoA, the oxidation product of pyruvate, fatty acids, and certain amino acids (not shown), is oxidized by the reactions of the citric acid cycle within the mitochondrial matrix. The principal products of the cycle are the reduced coenzymes NADH and FADH, and C02. The high-energy electrons of NADH and FADH2 are subsequently donated to the electron transport chain (ETC), a series of electron carriers in the inner membrane. The terminal electron acceptor for the ETC is 02. The energy derived from the electron transport mechanism drives ATP synthesis by creating a proton gradient across the inner membrane. The large folded surface of the inner membrane is studded with ETC complexes, numerous types of transport proteins, and ATP synthase, the enzyme complex responsible for ATP synthesis. 

The high mobility of the proton is coimected to the special transport mechanism and the structure of the water molecule. Protons in other types of solvents exhibit a mobility similar to other ions. However, the special transport mechanism can be transferred to migration of hydroxide ions in water because they are also part of the... 

The most important property of PVPA is conductivity based on hydrogen bonding, which allovt proton transport via a Grotthuss type mechanism (structural diffusion). The conductivity is the key property of PVPA, which is successfully used to obtain polymer electrolyte membranes by copolymerization or blending with appropriate materials. The applications of these materials have greatly expanded and now have many roles in the modern industrial economy. 

Biochemical ion-transfer reactions, and especially proton-transfer reactions, are enormously important for life. They are used in catalysis of acid-base reactions and enzymatic catalysis, or to establish concentration gradients in living cells. Many biomolecules exhibit proton-transport chaimels through which protons may be transported. These ehannels are designed by the molecule s structure, and generally filled with a small amount of water molecules. The water in this eonfined system is used to transport the proton via a Grotthuss-type mechanism. 

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