New electrochemical cells with membrane-electrode-assembly generating protonic heterojunctions “inorganic proton conductor–hydrogenated metal”

Abstract

Electrochemical cells “hydrogenated metal–proton conductor–any second electrode” are of certain applied interest in connection with the development of the protonic heterojunction conception as an alternative to the three-phase-boundary conception. The first, but not single condition of the formation of protonic heterojunction is the heterogeneous contact of hydrogen-containing materials such as the hydrogenated metal and the proton conductor. The appropriate couples consisting of Pd or Ti in the role of electrodes and solid hydroxides in the role of proton conductors have been studied. The way of the preparation of such original electrochemical cells and their behavior in the temperature range 320–430 K are presented. A stable electromotive force (emf) of various electrochemical cells ‘(Pd)|NaOH, KOH|(Pd)’, ‘(Pd)|CsHSO 4 |(Pd)’, ‘(Ti)|KOH·H 2 O|(C)’, ‘(Ti)|KOH·H 2 O|(Ti)’ has been observed. (Here (Pd), (Ti), (C) mean the main part of electrodes omitting the description of heteroboundaries.) The value of emf varies from 0.8 V to 1.4 V depending on physicochemical conditions. A certain part of this emf (0.8 V for Pd-cells and 0.2 V for Ti-cells) is due to heteroboundaries “hydrogenated metal–proton conductor”, which is found to be kinetically reversible to proton exchange. Isotopic effects of emf are the plain evidence in favor of potential determining role of protons. These data confirm the protonic heterojunction formation in electrochemical cells under study. It has given the impetus to working out the promising electrochemical devices with protonic heterojunctions.