III International Conference

PP-I-6iii) The magnitude of above mentioned difference of OCV of isotopically differentheterostructures (~120 mV) could be explained as the manifestation of the quantum effect ofenergy levels of protons both in hydroxide and Pd.To deeper understanding of proton exchange process, the comparison study of isotopicexchange in three system at 370 K: a = “PdH x -D 2 ” b = “KOH.H 2 O-D 2 ”, andc = “KOH.H 2 O|Pd,D 2 ”, has been performed. The experimental conditions are shortly: initialgas pressure was 5,3 kPa; surfaces of phase contacts were ~1 cm 2 ; Pd foil was 100 micronthick; hydroxide layers were 1,5 mm; the ratio “gas-solid” was approximately 1:1 in all casesIn the system “c” hydroxide was covered by Pd so to avoid any contact gas-hydroxide.Isotopic exchange in “a” system was enough fast, as expected, and determined by twoprocesses: surface chemical reaction on foil and changing in total pressure because isotopicexchange affect hydrogen solubility. In any case the complete equilibrium has been achievedin 20 minutes.Running of isotopic exchange in “b” was determined by surface chemical reaction. The90%-equilibrium has been achieved in 6 hours. At chosen conditions the magnitude of ratewas ~ 10 -7 mole atomH/cm 2 sec. By changing of gas pressure and/or size of solid it could bepossible to determine the rate of proton diffusion in the bulk of hydroxide as 5.10 -8 cm 2 /sec.Running of isotopic exchange in “c” was quite another than in “a” and “b”.Approximately during one hour the rate was relatively slow. Most probably it is determinedby hydrogen solubility in initially “empty” Pd foil. However, after ~ 90 minutes the rate ofisotopic exchange sharply increased to 10 -5 mole atom H/cm 2 sec, i.d. by two order of themagnitude higher, than for “b”. Since systems “b” and “c” had have the same ionic phase(KOH.H 2 O), one could conjuncture that increase of the rate of isotopic exchange was due tohigher chemical activity of monoatomic form of hydrogen in Pd in comparison withmolecular H 2 as the partner of hydroxide in case “b”. Therefore one can speak about highcatalytic activity of hydrogen in Pd. It is also very important to underline that in system “c”(likey in “b” too) there is no so named triple-phase-boundary, only interphase of metallic &ionic compounds, both hydrogen-containing. Basing on this optimistic conclusion one couldcome to a decision on the necessity to test the protonic heterojunction under our studyPdH x |KOH.H 2 O as a component of model fuel cell or a rechargeable battery.The presented results will be partially published in Solid State Ionic (2007) as Proceedingof International Conference on Solid State Proton Conductors (SSPC-13, September 2006.St-Andrews, Scotland, UK).This activity is supported by the Programme of Basic Research of Presidium RAS (P-03-02).18