III International Conference

ISOTOPIC METHODS AT THE STUDY OF ELECTROCHEMICAL ANDCATALYTIC PROCESSES IN PROTONIC HETEROJUNCTIONSPP-I-6Baikov Y.M.Ioffe Physical Technical Institute of RAS, St-Petersburg, RussiaE-mail: baikov.solid@mail.iofef.ruProtonic heterojunctions PdH x |KOH.H 2 O, x < 0.1, have been created by electrochemicalactivation of heterostructure Pd|KOH.H 2 O|Pd . The direct interfacial exchange namely byprotons has been demonstrated by using isotopes (H&D) as the label. A comparison of theexperimental and theoretical values of the isotopic effects in equilibrium has showed thatquantum effects contribute to the potential of protonic heterojunction. The catalytic action ofthe heterojunction’s boundary is discussed from viewpoint of using protonic heterojunction inelectrochemical devices.Protonic heterojunctions as a particular case of ionic ones are characterized by thereversible exchange of cations of hydrogen (protons) through the boundary between twophysically and/or chemically discriminate condensed phases. The possibility of a directobservation of such exchange originate from the existence of isotopically different atomicspecies. Such experiments allow to clarify some details of kinetic behavior or energetic stateof atoms of given chemical element. It is very important at the study of catalytic andelectrochemical processes. Phase interfaces are sometimes out-of-the-way places in the courseof the process under study, even for modern strong different kind of a spectroscopy.Historically, three approaches have been developed in the application of isotope methodsto the investigations: isotope label, isotopic effect and isotopic exchange. To study theequilibrium and kinetic processes in the heterostructure PdH x |KOH.H 2 O|M, where M=Pd, Ag,Ni, C, synthesized firstly by us, all of this variants of isotopic method have been used.Three interesting results have been obtained.i) Remarkable rate of isotopic exchange at 370 K in the system, initially described as“KOH.H 2 O(solid)|Pd(H,D) x |KOD.D 2 O(solid)”, has confirmed the reversible transfer ofhydrogen ion (H + /D + ) through the boundary “hydroxide-palladium” in both (!) directions.Note: Both hydroxide phases have had no contact with each other, being separated by Pd foil.ii) Arising from the electrochemical activation OCV (open curciut voltage) onheterostructures “PdH x |KOH.H 2 O(solid)|M” and “PdD x |KOD.D 2 O(solid)|M” has varieddepending on isotopic composition of hydrogen (1200 mV and 1320 mV, correspondingly, atM=C, 368 K). This result was considered as the evidence for potential-determining role ofprotons in equilibrium state of heterostructures under study.17