Proton hopping process

Apart from the problems of low electrocatalytic activity of the methanol electrode and poisoning of the electrocatalyst by adsorbed intermediates, an overwhelming problem is the migration of the methanol from the anode to the cathode via the proton-conducting membrane. The perfluoro-sulfonic acid membrane contains about 30% of water by weight, which is essential for achieving the desired conductivity. The proton conduction occurs by a mechanism (proton hopping process) similar to what occurs... 

The mechanism of long-range proton transfer processes in solutions is complex becanse seqnential proton hops from initial proton donors to proton acceptors are mediated by water (or solvent) molecules or other groups capable of ionization. 

Proton transfer proton transfer is a translocation of the protons in condensed media and molecular systems by means of any microscopic mechanism of proton transfer. The latter may involve (1) vehicle motion of the hydrogen ion, (2) proton hopping between two molecular species, (3) a shift of the proton within a molecular structure. The motion of the hydrogen ion is a diffusion process. Two other mechanisms represent elementary reaction steps involving breaking and formation of chemical bonds and may be characterized by the reaction rate constant... 

The Hj molecular ion plays the pivotal role in the ion-neutral reactions scheme now generally believed to be the major mechanism for the chemical evolution of dense molecular clouds. Hj is produced through cosmic ray ionization of H followed by the ion-neutral reaction (1). Since the latter reaction is extremely fast, the rate-determining process for the production of HJ is the cosmic ray ionization, whose rate is generally taken to be f a 10"g-i 63.68 main destruction mechanism of Hj is the proton-hop reaction (2). 

The sohd-state stmctures of crystal forms A (35b) and B (35a) (Scheme 26) have been determined by NMR methods. Form B was found to undergo an exchange process consisting of simultaneous proton hopping and internal... 

The dependence of the dc conductivities and the parameters derived thereof show that there are distinct differences between the ion dynamics in PDADMAC-rich and PSS-rich PEC. In both cases, however, the Arrhenius dependence of clearly shows that the ion dynamics in PEC materials is determined by the thermally activated hopping processes of the mobile ions. The fact that the isothermal dc conductivity increases continuously with NaPSS content indicates that the chloride ions do not dominate the ion transport, even in PEC materials with an excess of polycations and thus Cl as the most abundant mobile charge carrier. Otherwise, aac as a function of x should pass through a minimum, which is obviously not seen experimentally. The conductivity measured for PEC with x < 0.50 could therefore be either due to residual Na ions or protons. To shed more light on this aspect, PEC in which the sodium ions were replaced by lithium or cesium ions were studied. These results are discussed in the following section. 

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