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Advanced themes of scientific talk about protonic conductors

January 27th, 2012

I would like to propose for starters to divide the set of subjects onto two groups according to remarks in “Introduction” about preferably my personal interest (items ”a” and “b”) and evidently common interest (items “c” and “d”). Of course such division has enough relative character, but, by my opinion, it seems suitable.

Hydroxides and Isotopes into Protonic Conductor Class

My personal interest (items ”a” and “b”) relates to little know hydroxide proton conductors and to the special technique of intensive application of isotopic methods. The set of own articles in these directions are now partially on this site. This list will be extended, I hope, due to common efforts. Alkaline metals hydroxides have turned out mostly far interest of ionic community even in comparison with less thermal stabile rare-earth hydroxides. Hydroxide protonic conductors (HPC) revealed by us in the course of pioneering researches last five years. These HPC as complex compounds on the base of individual alkaline hydroxides in the form of crystalline hydrates and solid eutectics are particular points of phase diagramms Fig. 1-1 well known in physical chemistry. However only after our investigations it was revealed that they have more higher conductivity Fig. 1-2 at lower temperatures range in comparison with closely related acidic salts and perovskite proton conductors. OK? We affirm that our HPC are, namely, protonic conductors. The direct evidence in favor of that the isotopic effect of conductivity Fig. 1-3, 1-4 at the substitution protium for deuterium in electrolyte. OK? It is necessary to highlight that all three isotopic methods – isotopic label, isotopic exchange and isotopic effect – are very effective namely for study of hydrogen-containing systems.

Proton Mobility: Conductivity, Self-Diffusion and Chemical Liability

The Conductivity Fig.2-1 of individual hydroxides LiOH , NaOH and KOH are remarkably lower in the same temperature range than for their crystalline hydrates an eutectics. The Self-diffusion of hydrogen Fig.2-2 species are faster than ones of other ions (O2-, K+ and Na+) . The ratio Nernst –Einstein indicate that there is different ways for ions in chotic thermal migration and a movement in the electric field. The discussion of similar data for other inorganic proton conductors is extremely few Kreuer (1996, 1998). Probably, a resistance could be measured sufficiently lighter than a selfdiffusion.(?) The complete thermo-chemical stability of nominally anhydrous LiOH, NaOH and KOH and their eutectic as well as a eutectic LiOH+1.5NaOH up to melting point were observed in inert gaseous and hydrogen. The solid crystalline hydrates under study Fig.1-1 were enough stable because experiments have been performed in closed volume where equilibrated water pressure was not higher than 5 mm Hg. Up to melting points. Therefore our hydroxides turned out more thermostable! OK? Heat capacity and DSC spectra Fig.2-3 have been studied enough detail. We used DSC to study phase transitions in solid state of eutectics. Optic properties and infrared and Raman spectroscopy were not study by us because it is not our business and there are enough data in literature. Chemical properties have been studied from two viewpoints: general chemistry and an ability to isotopic exchange. The reactivity of SOLID hydroxides and their derivates are interesting for experiments and for applied using not only at all, but against concrete components of invironmental, namely water vapor and CO2. The most unexpected phenomenon is high tolerance to DRY CO2 below 360 K. This point is characterized also for the conductivity of KOH Fig. 1-2 . This fact will be studied futher. Such distinction could be connected with different chemical activity anions OH- and SO4-. By the way such, effect correlate with the conclusion Wilmarth and Dayton (mid XX-th centure) that water solution of alkali was catalyzed H↔D exchange with H2 in contrary to solution of H2SO4 (!). It is interesting that classical protonic conductor CsHSO4 (acid salt) do not reacts with water vapor and CO2 . Is it OK? This fact correlates with ability to isotopic exchange Fig.2-4 of hydroxides with molecular hydrogen in contrary to acidic salts.

Electrochemistry activity: EMF, Exchange Current, Protonic Heterojunction

Electrocemical activity is not pure private properties of any material. Its manifestation is due to , as a rule, the properties of the heteroboundary e.g between electrode|electrolyte. There are the couple of it main characteristics: thermodynamical (EMF) and kinetic (exchange current, I0) one. EMF (or maybe more exactly open circuit potential) of different heteroboundaries Tabl.1 are strongly depends not only on main physical and chemical nature of components, but also on their isotopic composition (H/D) Tabl.2. The latter is the evidence in favor of potential-determining role of hydrogen-containing species (maybe protons) on corresponding boundary. Very interesting heterodoundaries is those if an electrode is hydrogen-containing compound also, e.g. hydrogen solution in metal. Such situation is analogous to one in Li- and Ag-ion electrochemical devices. Special experiments have been proved the direct hydrogen species’s exchange between, e.g. PdHx|KOH·H2O. Such phenomenon could be named as protonic heterojunction Fig.3-1. It is interesting that the magniy
yudes of electrochemical I0 correlates with the isotopic I0 D2- KOH H2O Fig.3-2 The isotopic shift of heterojunction’s potential of “A | protonic”, where A= C, Si, Sn, is observed also. {Tabl.1) Moreover, Cyclic Current-Voltage curves for isotopically different cells did not coincide. Fig. 3-3. It is necessary to highlight that a.m. data obtained by isotopic methods have not analogy in other proton conducting systems. OK??
In the course of investigations of hydroxide protonic conductors some data useful from applied viewpoint have been received. First one is the crucial role of self-organized microheterogenety of eutectics in sufficient increase of conductivity Fig. 3-4 in comparison with pristine individual components. The second applied orienting results concerned with the opportunity to prepare low-drain and small-sized sources for micro-electronic devices. Such home-made battery provided the work of electronic clock more than half-year.
The protonic conductors on the base of alkaline hydroxide must be accepted for Class of Protonic Conductors as the object for both fundamental and applied researches. It is necessary to underline that hydroxide protonic conductors has given the sample of effective use of isotopic methods. It seems now that hydroxide protonic conductors could be used as primary or secondary batteries of low-drain and small-sized ones at temperature around 200-400 K.
P.S. I tried to avoid the comparison of different families of protonic conductors from the viewpoint of temperature range. It would be awfully interesting to collect such data under the conception on Corresponding States. Fig. 4-1

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